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Four new functionalized Ni(II) dithiocarbamate complexes of the formula [Ni(L x ) 2 ] (1-4) (L 1 = N -methylthiophene- N -3-pyridylmethyl dithiocarbamate, L 2 = N -methylthiophene- N -4-pyridylmethyl dithiocarbamate, L 3 = N -benzyl- N -3-pyridylmethyl dithiocarbamate, and L 4 = N -benzyl- N -4-pyridylmethyl dithiocarbamate) have been synthesized and characterized by IR, UV-vis, and 1 H and 13 C{ 1 H} NMR spectroscopic techniques. The solid-state structure of complex 1 has also been determined by single crystal X-ray crystallography. Single crystal X-ray analysis revealed a monomeric centrosymmetric structure for complex 1 in which two dithiocarbamate ligands are bonded to the Ni(II) metal ion in a S^S chelating mode resulting in a square planar geometry around the nickel center. These complexes are immobilized on activated carbon cloth (CC) and their electrocatalytic performances for the oxygen evolution reaction (OER) have been investigated in aqueous alkaline solution. All the complexes act as pre-catalysts for the OER and undergo electrochemical anodic activation to form Ni(O)OH active catalysts. Spectroscopic and electrochemical characterization revealed the existence of the interface of molecular complex/Ni(O)OH, which acts as the real catalyst for the OER. The active catalyst obtained from complex 2 showed the best OER activity achieving 10 mA cm -2 current density at an overpotential of 330 mV in 1.0 M aqueous KOH solution.

Five new heterometallic Cu(ii)-Mn(ii) discrete trinuclear complexes, [(CuL)2Mn(CH3COO)2] (1), [(CuL)2Mn(NO3)2] (2), [(CuL)2Mn(C6H5COO)(H2O)]Cl (3), [(CuL)2Mn((p-OH)C6H5COO)(H2O)]ClO4 (4) and [(CuL)2Mn(HCOO)(H2O)]ClO4 (5), have been synthesized using a metalloligand, CuL derived from an N2O2 donor Schiff base, H2L (N,N'-bis(α-methylsalicylidene)-1,3-propanediamine). Single-crystal structural analyses reveal that all five complexes have a common [(CuL)2Mn] core, where two terminal metalloligands, CuL, are connected to the central metal ion, Mn(ii), via double phenoxido bridges. Among the complexes, 1 and 2 possess linear structures where the terminal Cu(ii) atoms are bridged to the central Mn(ii) atoms by acetate and nitrate ions, respectively along with the double phenoxido bridges, whereas 3, 4 and 5 have bent structures in which the respective anionic coligands, benzoate, p-hydroxybenzoate and formate ions are coordinated only to central Mn(ii) in monodentate fashion along with a water molecule that completes its hexa-coordinated geometry. Among the complexes, 1, 3, 4 and 5 show quite high bio-mimicking catecholase-like activity for the aerial oxidation of 3,5-di-tert-butylcatechol with turnover numbers (Kcat) of 139 h-1, 439 h-1, 348 h-1 and 730 h-1, respectively, whereas complex 2 is practically inactive towards this reaction. The presence of the coordinated water molecule to Mn(ii) in the bent complexes, 3-5, appears to be responsible for their high catalytic activity and the difference in their activity may be attributed to steric crowding due to the anionic coligand, whereas the inactivity of 2 seems to be associated with the low basicity of the nitrate ion. The temperature-dependent dc molar magnetic susceptibility measurements reveal that complexes 1-5 are antiferromagnetically coupled with the exchange coupling constants (J) = -8.54 cm-1, -11.50 cm-1, -19.83 cm-1, -10.65 cm-1 and -10.27 cm-1 for 1, 2, 3, 4 and 5 respectively as is expected from the Cu-O-Mn bridging angles.

Four new heteroleptic Ni(ii) complexes with general formula [Ni(ii)(LL')] (L = 2-(methylene-1,1'-dithiolato)-5-phenylcyclohexane-1,3-dione (L1) and 2-(methylene-1,1'-dithiolato)-5,5'-dimethylcyclohexane-1,3-dione (L2); L' = 1,2-bis(diphenylphosphino)ethane (dppe) and bis(diphenylphosphino)monosulphide methane (dppms) have been synthesized and characterized by elemental analysis and spectroscopy (IR, UV-Vis, 1H, 13C{1H} and 31P{1H} NMR). All complexes 1-4 have also been characterized by PXRD and single crystal X-ray crystallography. The solid state molecular structures revealed distorted square planar geometry about the four-coordinate Ni(ii) metal centre together with rare NiH-C intra/intermolecular anagostic interactions in axial positions. In these complexes supramolecular structures have been sustained by non-covalent C-HO, C-OH-O, C-Hπ, C-Hπ (NiCS2, chelate), ππ and HH interactions. Their electrocatalytic properties have been investigated for oxygen evolution reaction (OER) in which complex 2 showed the highest activity with 10 mA cm-2 at the potential of 1.58 V vs. RHE. In addition, complex 2 also exhibits an OER onset potential at 1.52 V vs. RHE.

Correction for 'Tri- and hexa-nuclear NiII-MnII complexes of a N2O2 donor unsymmetrical ligand: synthesis, structures, magnetic properties and catalytic oxidase activities' by A. Ghosh et al., Dalton Trans., 2018, 47, 13957-13971.

New complexes [Mo(η3-C3H5)X(CO)2(4-Y-BIAN)] (4-Y-BIAN = bis(4-Y-phenyl)-acenaphthenequinonediimine), with X = Br and Y = H, Me, OMe, COOH and X = Cl, Y = OMe, as well as the cation with X = NCMe and Y = OMe were synthesized, expanding the scope of this family. Two single crystal X-ray structures (X = Br, Y = Me, OMe) display a less symmetric arrangement (axial isomer), where one N donor atom is trans to the allyl group and the second to one CO. DFT studies showed similar energies for the two possible isomers of the complexes, with a very small preference for the observed axial isomer. The HOMO of the complexes is localized in the metal and the HOMO-1 of the oxidized species has a contribution from the BIAN ligand, while the LUMO is fully localized in BIAN. Electrochemical studies showed one process corresponding to the oxidation of Mo(ii) to Mo(iii) for complexes with X = Br, Y = H, Me, and two oxidation reactions for those with X = Br, Y = Cl, OMe, while the COOH derivative exhibited no oxidation wave. The antitumor effect of the complexes with X = Br was tested in cancer lines, and the H and OMe complexes were particularly active, with EC50 values below 8 μM in HeLa cell lines. The DNA binding constants determined by titration experiments were comparable with those of doxorubicin and ethidium bromide, suggesting a mechanism of action based on intercalation in DNA.

A new benzimidazolyl terpyridyl ligand (BIT) selectively detects Fe2+, F- and CN- ions in acetonitrile. The Fe2+ complex [Fe(H-BIT)2]·(ClO4)4 (1) displays the fast and selective detection of 2,4,6-trinitrophenol (TNP) with strong binding (log β = 8.51 ± 0.24) and a low limit of detection (1.4 × 10-7 M) among several nitroaromatics. The color of complex 1 changes from purple to red, yellow, and green upon the separate addition of 2,4,6-trinitrophenol and tetrabutylammonium salts of fluoride and cyanide, respectively. The overall color changes thus display a model of a traffic light. The structures of BIT, 1 and [Fe(BIT)2]·(TNP)2 (2) have been well characterized using spectroscopic techniques and single crystal X-ray crystallography.

A facile and reliable method to monitor strongly acidic pH was developed. The sensing mechanism was found to involve the protonation-deprotonation equilibrium of the synthesized probe HQphy (1) (N-phenyl-N'-quinoxalin-2-ylmethylene-hydrazine) within a working range of pH 0.7-2.7. The eventual sensing of Fe3+ was the outcome of acidity imparted by [Fe(H2O)6]3+ ions in solution during the formation of [Fe(H2O)5(OH)]2+. The protonation-deprotonation phenomenon of HQphy was investigated using 1H NMR and single crystal X-ray diffraction experiments. The protonated probe, H2Qphy+, was crystallized with FeCl4-/ClO4- counter anions as [H2Qphy][FeCl4]·H2O (2)/[H2Qphy][ClO4]·H2O (3). A further complex containing the [H2Qphy] cation (4) was also formed. The complexes were characterized by SC-XRD experiments. Moreover, single crystal to single crystal transformation is observed between 1 and 3. In order to understand the sensing mechanism, various analytical studies, such as UV-Vis titration, ESI-MS spectrometry analysis and 1H NMR, were carried out in detail. A theoretical study correlates well with the experimental data, where the π(L) → π*(L) transition of the ligand is red shifted by 100 nm due to protonation of the quinoxaline moiety. The probe enables discrimination of trihalo acetic acid from its mono- and di-analogues.

Eight novel Tl(i) β-oxodithioester complexes, [TlL]n (1-8), with ligands, L = methyl-3-hydroxy-3-(2-furyl)-2-propenedithioate (L1), methyl-3-hydroxy-3-(2-thienyl)-2-propenedithioate (L2), methyl-3-hydroxy-3-(3-pyridyl)-2-propenedithioate (L3), methyl-3-hydroxy-3-(4-pyridyl)-2-propenedithioate (L4), methyl-3-hydroxy-3-(9-anthracenyl)-2-propenedithioate (L5), methyl-3-hydroxy-3-(4-fluorophenyl)-2-propenedithioate (L6), methyl-3-hydroxy-3-(4-chlorophenyl)-2-propenedithioate (L7) and methyl-3-hydroxy-3-(4-bromophenyl)-2-propenedithioate (L8), were synthesized and thoroughly characterized by elemental analysis, and IR, UV-Vis, 1H and 13C{1H} NMR spectroscopy, and their structures were ascertained by X-ray crystallography. Complexes 1 and 2 crystallized in P21 and P212121 chiral space groups, respectively, and were studied using Circular Dichroism (CD) spectra. Solid state structural analyses revealed that the β-oxodithioester ligands are bonded to Tl(i) ions in (O, S) chelating and chelating-bridging modes, thereby forming different types of 1D and 2D coordination polymeric structures. By considering the metal-assisted bonding interactions, various coordination numbers of 5-8 and 10 are established around the metal centre. Except for 5 and 7a which have TlTl separations at 3.724(1) and 3.767(1), 3.891(1) Å respectively, the remaining complexes have no TlTl distances <4.0 Å. This indicates that the majority of structures contain only weak inter- and intramolecular thallophilic interactions. The structures of 1-8 highlight the role played by variations in substituents in the dithioester unit in the structure and properties of the complexes. The multi-dimensional assembly in these complexes rests on important non-covalent C-Hπ (TlOSC3, chelate), C-HX (X = F, Cl, O, N), C-Hπ, HH and rare TlH-C intermolecular anagostic interactions. The TlH-C anagostic interactions together with C-OTl and C-STl interactions formed 7-, 11- and 12-membered chelate rings about the metal centers. The anagostic interactions in 1, 2 and 7b were assessed by theoretical calculations. All the complexes showed bright green luminescent emissions in solution and solid phases. Time-resolved emission spectra revealed a triexponential decay curve and short mean lifetime for fluorescence behavior.

Polyoxometalates (POMs) are highly versatile materials if paired with various conducting supports. We here present a new prospective approach for obtaining advanced electrocatalytic systems via POMs (1 and 2) nanostructured on Ni foam (NF) to give bimetallic nanohybrid composite materials M0.4Ni0.6/WO3 (M = Rh (3) or Ir (4)). By this pathway, two rare isopolyoctatungstate-based organometallic clusters [Hx(MCp*)4W8O32]·yH2O (in 1, M = Rh, x = 8, y = 23; in 2, M = Ir, x = 4, y = 17.33) have been synthesized via one-pot reactions using [Cp*MCl2]2 (Cp* = pentamethylcyclopentadienyl, M = Rh or Ir) and Na2WO4·2H2O in basic conditions. Compounds 1 and 2 were successfully nanostructured on the surface of commercially available NF and were thermally reduced to M0.4Ni0.6/WO3 (M = Rh (3) or Ir (4)) after annealing at 400 °C for 8 h in a 15% H2/N2 atmosphere. Electrodes modified with the POMs 3 and 4 exhibited remarkable HER activities in a 1 M KOH solution and achieved a current density of 10 mA cm-2 at low overpotentials of about 67 and 35 mV versus RHE, with Tafel slopes of 56 and 34 mV dec-1, respectively.

A new mononuclear Ni(ii) complex, [NiL] (1) of an unsymmetrically dicondensed N2O2 donor ligand, H2L (where H2L = N-α-methylsalicylidene-N'-salicylidene-1,3-propanediamine), has been synthesized. Complex 1, on reaction with Mn(ii) in the presence of different co-anions, yielded three heterometallic NiII-MnII complexes, [(NiL)2Mn(NCS)2]·CH3CN (2), [(NiL)2Mn(N3)(H2O)](ClO4)·H2O (3) and [{(NiL)2Mn(H2O)}2(μ1,3-N3)](ClO4)3 (4). Single crystal structural analyses show that complexes 2 and 3 contain similar bent trinuclear NiII2MnII structures, with the difference that in complex 2 two SCN- ions and in 3, one N3- and one H2O molecule are coordinated to the Mn(ii) centre. Complex 4 possesses a hexanuclear structure, in which two trinuclear NiII2MnII units are connected via a single μ1,3-azido bridge. Variable temperature dc molar magnetic susceptibility measurements reveal that the two Mn(ii) centres in complex 4 are antiferromagnetically coupled with an exchange coupling constant (J) of -3.73 cm-1. Among the three heterometallic complexes, only 3 and 4 show bio-mimetic catalytic oxidase activities. For catecholase like activity, the turnover numbers (Kcat) of complexes 3 and 4 are 984 and 2081 h-1, respectively, whereas for phenoxazinone synthase-like activity, the turnover numbers of complexes 3 and 4 are 6351 and 10 545 h-1, respectively. The high catalytic oxidase activities of complexes 3 and 4 in contrast to the inactivity of complex 2 are attributed to the coordination of a water molecule to the Mn(ii) centre in the former structures, which facilitates the binding of the substrate with the catalyst. Mass spectral analyses suggest the probable formation of a complex-substrate intermediate in these catalytic reactions and cyclic voltammetry measurements show that Ni(ii) is reducible to Ni(i).

Two new N 2 O 3 donor ligands N-(3-methoxysalicylidene)-N'-(salicylidene)-1,3-propanediamine (H 2 L 2 ) and N-(3-methoxysalicylidene)-N'-(α-methylsalicylidene)-1,3-propanediamine (H 2 L 3 ) and their Cu(ii) complexes have been synthesized. Using these complexes and another Cu-complex with one asymmetric N 2 O 2 donor ligand N-(α-methylsalicylidene)-N'-(salicylidene)-1,3-propanediamine (H 2 L 1 ) as metalloligands, four new heterometallic Cu(ii)-Mn(ii) complexes [(CuL 1 ) 2 Mn 2 Cl 4 ]·3CH 3 OH (1), [(CuL 1 ) 2 MnCl 2 ]·2CH 3 CN (2), [CuL 2 MnCl 2 ]·H 2 O (3) and [CuL 3 MnCl 2 ] (4) have been synthesized with MnCl 2 ·4H 2 O. The tetranuclear (1) and trinuclear (2) complexes were prepared by varying the ratio of the metalloligand [CuL 1 ] and MnCl 2 whereas dinuclear complexes 3 and 4 are the sole products irrespective of the metalloligand : MnCl 2 ratio. All the complexes 1-4 were structurally characterized by single crystal X-ray diffraction. The tetranuclear (CuMn) structure of 1 is formed by the dimerization of phenoxido bridged Cu II Mn II units whereas the bent CuMn II trinuclear species 2 is formed by the coordination of two metalloligands (CuL 1 ) to Mn(ii) via a diphenoxido bridge. Complexes 3 and 4 possess a similar dinuclear Cu II Mn II structure in which two phenoxido groups form a bridge between the two metal centres. The variable temperature dc magnetic susceptibility measurements reveal that the Cu(ii) and Mn(ii) ions are antiferromagnetically coupled in all the complexes, 1-4. The values of exchange coupling constants (J Mn-Cu ) are -45.54, -39.66, -71.54 and -48.40 cm -1 for complexes 1-4, respectively. A DFT study of all the complexes has also been performed to rationalize the experimental results of magnetic measurements.

Three novel water soluble neutral mononuclear oxidovanadium(iv) complexes 1-3, [VOLB 2 ] (where H 2 L = dipicolinic acid (DPA) and B = imidazole (1)/1-methylimidazole (2)/1-allylimidazole (3)), were synthesized by the reaction of [VOL(H 2 O) 2 ] with imidazole/1-methylimidazole/1-allylimidazole in ethanol. The complexes were thoroughly characterized by elemental analysis, IR, UV-Vis and EPR spectroscopy, magnetic susceptibility, cyclic voltammetry and single crystal X-ray diffraction techniques. In all the complexes the vanadium(iv) centre assumes a distorted octahedral environment. All the three complexes have similar structures and contain a range of intramolecular interactions such as hydrogen bonding, C-Hπ, and ππ stacking dominating their supramolecular architectures. A thermal study of the complexes was carried out to analyze their stability. The energy of non-covalent interactions and frontier orbitals for the complexes were also calculated by DFT. In order to investigate the binding interactions and conformational changes of the secondary structure of bovine serum albumin (BSA) with the complexes, absorption, fluorimetric titration and circular dichroism measurements in aqueous medium were carried out. Molecular docking studies have also been carried out to understand the binding modes and interaction patterns of the oxidovanadium(iv) complexes with BSA. The anticancer activities of the ligand and complexes 1-3 were tested against the human hepatic carcinoma cell line Hep3B. The complexes showed prominent cytotoxicity towards cancer cells.

The reaction of 2-hydroxybenzoylhydrazine (H 2 bh) separately with equimolar amounts of [V IV O(aa) 2 ] and [V IV O(ba) 2 ] in CHCl 3 afforded the complexes [VO 3 (HL 1 ) 2 ] (1) and [VO 3 (HL 2 ) 2 ] (2) respectively in good to excellent yield ((HL 1 ) 2- and (HL 2 ) 2- represent respectively the dianionic form of 2-hydroxybenzoylhydrazones of acetylacetone (H 3 L 1 ) and benzoylacetone (H 3 L 2 ) (general abbreviation H 3 L)). From X-ray structure analysis, the V V -O-V V angle was found to be ∼115° and 180° in 1 and 2 respectively. Upon one-electron reduction selectively at one V centre at an appropriate potential, each of 1 and 2 generated mixed-valence [(HL)V V O-(μ-O)-OV IV (HL)] - species 1A and 2A respectively, which showed valence delocalization at room temperature and localization at 77 K, and the V IV -O-V V bond angles were calculated to be 177.5° and 180° respectively. The intercalative mode of binding of the two complexes 1 and 2 with CT DNA has been suggested by UV-visible spectroscopy (K b = 7.31 × 10 5 M -1 and 8.71 × 10 5 M -1 respectively for 1 and 2), fluorescence spectroscopy (K sv = 6.85 × 10 5 M -1 and 8.53 × 10 5 M -1 respectively for 1 and 2) and circular dichroism spectroscopy. Such intercalative mode of binding of these two complexes with CT DNA and HPV DNA has also been confirmed by molecular docking study. Both complexes 1 and 2 exhibited promising anti-cancer activity against SiHa cervical cancer cells with IC 50 values of 28 ± 0.5 μM and 25 ± 0.5 μM respectively for 24 h which is significantly better than that of widely used cisplatin (with IC 50 value of 63.5 μM). Nuclear staining experiments reveal that these complexes kill the SiHa cells through apoptotic mode. It is interesting to note that these two complexes are non-toxic to normal T293 cell line. Complex 2 showed higher DNA binding ability with CT DNA and HPV DNA as well as better anti-cancer properties towards SiHa cervical cancer cells in comparison to complex 1, a fact which can be explained by considering the lower energy of LUMO (which favours electron transition from DNA to the metal complex) and also the higher surface area of complex 2 in comparison to complex 1 due to the presence of one extra electron-withdrawing phenyl group in the former.

A new series of heterometallic trinuclear Cu 2 Ln complexes [lanthanide ions Ln = Gd (1), Tb (2), Dy (3), Ho (4) and Er (5)] has been synthesized using a Cu(ii)-metalloligand derived from a N 2 O 2 donor unsymmetrical Schiff base, H 2 L (where H 2 L = N-α-methylsalicylidene-N'-salicylidene-1,3-propanediamine), and structurally characterized. Among these complexes, [(CuL) 2 Gd(NO 3 ) 3 (CH 3 CN) 2 ] (1), [(CuL) 2 Tb(NO 3 ) 3 (CH 3 CN) 2 ] (2) and [(CuL) 2 Dy(NO 3 ) 3 (CH 3 CN) 2 ] (3) are isomorphic and isostructural. In these complexes two metalloligands coordinate to the central Ln(iii) (Ln = Gd, Tb and Dy respectively) ion in a transoid fashion viaμ 2 -phenoxido oxygen atoms. The Ln(iii) ions are deca-coordinated with a distorted tetradecahedron geometry. The two terminal Cu(ii) ions of the complexes possess a hexa-coordinated distorted octahedral geometry. In contrast, in complexes [(CuL) 2 Ho(NO 3 ) 3 (CH 3 CN)], (4) and [(CuL) 2 Er(NO 3 ) 3 (CH 3 CN)]·0.5(CH 3 CN) (5), the two metalloligands coordinated to the Ln(iii) ions in a cisoid fashion. The Ho(iii) ion in 4 is nona-coordinated with a distorted tricapped trigonal prismatic geometry and the Er(iii) ion in 5 is octa-coordinated with a distorted square antiprismatic geometry. The two terminal Cu(ii) ions in complexes 4 and 5 are penta-coordinated with a distorted square-pyramidal geometry. The dc magnetic susceptibilities and field dependent magnetization measurement of complex 1 reveal the occurrence of ferromagnetic interactions between Cu(ii) and Gd(iii) ions as well as intermolecular antiferromagnetic interactions. Both complexes 2 and 3 show ferromagnetic interactions between Cu(ii) and Ln(iii) ions. The ac magnetic susceptibilities of all the complexes were also recorded and it was found that only complexes 2 and 3 exhibit slow relaxation of magnetization reorientation below 10 K at 2000 Oe applied dc field, this being characteristic of single molecule magnets.

Refluxing [V IV O(β-diketonate) 2 ], namely [V IV O(acetylacetonate) 2 ] and [V IV O(benzoylacetonate) 2 ], separately with an equivalent or excess amount of 2-aminobenzoylhydrazide (ah) in laboratory grade (LG) CH 3 OH in aerobic conditions afforded non-oxidovanadium(iv) and oxidovanadium(v) complexes of the type [V IV (L 1 ) 2 ] (1), [V V O(L 1 )(OCH 3 )] 2 (3) and [V IV (L 2 ) 2 ] (2), and [V V O(L 2 )(OCH 3 )] (4), respectively. (L 1 ) 2- and (L 2 ) 2- represent the dianionic forms of 2-aminobenzoylhydrazone of acetylacetone (H 2 L 1 ) and benzoylacetone (H 2 L 2 ), respectively, (general abbreviation, H 2 L), which was formed by the in situ condensation of ah with the respective coordinated [β-diketonate] in medium-to-good yield. The yield of different resulting products was dependent upon the ratio of ah to [V IV O(β-diketonate) 2 ]. For example, the yield of 1 and 2 complexes increased significantly associated with a decrease in the amount of 3 and 4 with an increase in the molar ratio of ah. Upon replacing CH 3 OH by a non-hydroxylic solvent, LG CHCl 3 , the above reaction yielded only oxidovanadium(v) complexes of the type [V V O(L 1 )(OH)] 2 (5), [V V O(L 2 )(OH)] (6) and [VO 3 (L) 2 ] (7, 8) whereas, upon replacing CHCl 3 by another non-hydroxylic solvent, namely LG CH 3 CN, only the respective [VO 3 (L) 2 ] (7, 8) complex was isolated in 72-78% yield. However, upon performing the above reactions in the absence of air using dry CH 3 OH or dry CHCl 3 , only the respective [V IV (L) 2 ] complex was obtained, suggesting that aerial oxygen was the oxidising agent and the type of pentavalent product formed was dependent upon the nature of solvent used. Complexes 3 and 4 were converted, respectively, to 7 and 8 on refluxing in LG CHCl 3 via the respective unstable complex 5 and 6. The DFT calculated change in internal energy (ΔE) for the reactions 2[V V O(L 2 )(OCH 3 )] + 2H 2 O → 2[V V O(L 2 )(OH)] + 2CH 3 OH and 2[V V O(L 2 )(OH)] → [VO 3 (L 2 ) 2 ] + H 2 O was, respectively, +3.61 and -7.42 kcal mol -1 , suggesting that the [V V O(L 2 )(OH)] species was unstable and readily transformed to the stable [VO 3 (L 2 ) 2 ] complex. Upon one-electron reduction at an appropriate potential, each of 7 and 8 generated mixed-valence [(L)V V O-(μ-O)-OV IV (L)] - species, which showed valence-delocalisation at room temperature and localisation at 77 K. Some of the complexes showed a wide range of toxicity in a dose-dependent manner against lung cancer cells comparable with that observed with cis-platin.

A reaction of N 1 ,N 3 -bis(3-methoxysalicylidene) diethylenetriamine (H2Vd) and Zn(NO 3 ) 2 ·6H 2 O, ZnBr 2 , ZnI 2 and Cd(NO 3 ) 2 ·4H 2 O in a methanol solution led to zinc and cadmium complexes of different nuclearities, [Zn 2 (Vd·H) 2 (X) 2 ]·CH 3 OH (X = NO 3 , Br, I) [1a, 1b and 1c] and Cd 3 (Vd) 2 (NO 3 ) 2 (2). In 1(a-c), two H2Vd ligands bridge the two metal centers whereas in 2, they provide sideways support to two terminal Cd 2+ ions, providing an all-oxygen envelope to the central Cd 2+ ion. All four compounds were characterized by elemental analysis, FT-IR spectroscopy and single crystal X-ray diffraction analysis. Complexes 1(a-c) exhibit dinuclear structures, whereas 2 exhibits a nearly linear trinuclear structure. The structural differences among these complexes are attributable to various coordination modes and flexible configurations of the H2Vd ligand. The ligand H2Vd is an excellent probe for sensing Zn 2+ in solution, whereas complexes 1(a-c) are able to selectively detect pyrophosphate (PPi) in aqueous medium. The structure of the pyrophosphate (PPi) complex has been proposed using DFT calculations and the selectivity is due to the unique ability of this anion to simultaneously coordinate to both the Zn metal centers. The anticancer activity of complexes 1(a-c) was also explored.

Three new heteronuclear nickel(ii)/cadmium(ii) complexes, [(SCN)(Cl)Cd(L)Ni(DMF) 2 ] (1), [(SCN)(CH 3 CO 2 )Cd(L)Ni(CH 3 OH) 2 ] (2) and [(SCN)(Cl)Cd(L)Ni(NH 2 CH 2 CH 2 CH 2 NH 2 )] n (3) {where H 2 L = N,N'-bis(3-ethoxy-salicylidene)propane-1,3-diamine is a N 2 O 4 compartmental Schiff base}, have been synthesized and characterized. The structures of the complexes have been confirmed by single crystal X-ray diffraction studies. In each complex, nickel(ii) is placed in the inner N 2 O 2 environment and cadmium(ii) is placed in the outer O 4 compartment of the compartmental Schiff base. Furthermore, the importance of unconventional C-Hπ (chelate) interactions in the solid state of both complexes and C-Hπ (thiocyanate) interaction in complex 2 has been described by means of DFT and MEP calculations and characterized using NCI plots. All complexes show photoluminescence at room temperature upon irradiation by ultraviolet light. The lifetimes of excited states are in the range of 2-6 ns.

One Mn(II) coordination polymer, [Mn(o-(NO2)C6H4COO)2(pyz)(H2O)]n (1), has been synthesized and oxidized with n-Bu4NMnO4 in non-aqueous media to two mixed-valence hexanuclear Mn(II/III) complexes [MnIII2MnII4O2(pyz)0.61/(MeOH)0.39(o-(NO2)C6H4COO)10·(H2O)·{(CH3)2CO}2]·(CH3)2CO (2) and [MnIII2MnII4O2(pyz)0.28/(MeCN)3.72(o-(NO2)C6H4COO)10·(H2O)] (3) (where pyz = pyrazine). All three complexes were characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction analyses, and variable-temperature magnetic measurements. The structural analyses reveal that complex 1 is comprised of linear chains of pyz bridged Mn(II), which are further linked to one another by syn–anti carboxylate bridges, giving rise to a two-dimensional (2D) net. Complexes 2 and 3 feature mixed valence [MnIII2MnII4] units in which each of the six manganese centres reside in an octahedral environment. Apart from the variations in terminal ligands (acetone for 2 and acetonitrile for 3), the complexes are very similar. Using 3,5-di-tert-butyl catechol (3,5-DTBC) as the substrate, the catecholase-like activity of the complexes has been studied and it is found that the mixed valent Mn6 complexes (2 and 3) are much more active towards aerial oxidation of catechol compared to the Mn(II) complex (1). Variable-temperature (1.8–300 K) magnetic susceptibility measurements showed the presence of antiferromagnetic coupling in all three complexes. The magnetic data have been fitted with a 2D quadratic model derived by Lines, giving the exchange constant J/kB = −0.0788(5) K for 1. For 2 and 3, antiferromagnetic interactions within the Mn6 cluster have been fitted with models containing three exchange constants: JA/kB = −70 K, JB/kB = −0.5 K, JC/kB = −2.9 K for 2 and JA/kB = −60 K, JB/kB = −0.3 K, JC/kB = −2.8 K for 3.

New phenylmercury(II) complexes of the form [PhHg(L1), PhHg(L2) and PhHg(L3)] (L1 = methyl-3-hydroxy-3-(p-methoxyphenyl)-2-propenedithioate (1), L2 = methyl-3-hydroxy-3-(p-bromophenyl)-2-propenedithioate (2) and L3 = methyl-3-hydroxy-(3-pyridyl)-2-propenedithioate (3)) have been synthesized and characterized by elemental analysis, IR, UV-Vis, 1H and 13C NMR. The crystal structures of 1–3 reveal a linear geometry about the mercury atom via ipso-C and S11 atoms. 1 and 2 exhibited O,S-coordination whereas 3 preferred S,S-coordination. Intramolecular Hg∙∙∙O bonding interactions are also observed in 1 and 2 at distances of 2.638(14), 2.644(10) Å respectively. However in 3, incorporation of the 3-pyridyl substituent on the ligand enhanced the proximity of S13 and N14, giving rise to significant intramolecular Hg∙∙∙S and intermolecular Hg∙∙∙N interactions at 3.141(5) Å and 2.77(2) Å respectively generating a 1-D polymeric chain motif. The O,S- or S,S-coordination preference and Hg∙∙∙N interactions have been assessed by DFT calculations. All the complexes show metal perturbed ligand-centred luminescence characteristics in solution and in the solid phase. The band gap values 2.54, 2.66 and 2.61 eV for 1, 2 and 3, respectively, evaluated from the diffuse reflectance spectroscopy show the semiconducting nature of the complexes.

Crystal structures of novel pyridyl functionalised [Tl(L)]∞ (L = (N-benzyl-N-methylpyridyl) dithiocarbamate(L1) 1, bis(N-methylpyridyl) dithiocarbamate(L2) 2, (N-methyl(1,4-benzodioxane-6-yl)-N-methylpyridyl)dithiocarbamate(L3) 3, (N-ferrocenyl-N-methylpyridyl) dithiocarbamate(L4) 4) complexes revealed rare intermolecular C-H···Tl anagostic and C-S···Tl interactions forming a six-membered chelate ring about the metal center, which have been assessed by DFT calculations. The strong thallophilic bonding is responsible for the strong luminescent characteristics of the complexes in the solid phase.

Aqueous solution of sodium molybdate reacts with aromatic thiohydrazides like thiobenzhydrazide, 2-hydroxythiobenzhydrazide, furan-2-thiohydrazide and thiophen-2-thiohydrazide to form green, neutral diamagnetic 1 : 3 chelates. They were characterized by elemental analysis and spectroscopic methods. Tris(2-hydroxythiobenzhydrazido)molybdenum(vi) was crystallized from benzene and the crystal structure shows that molybdenum(vi) is hexacoordinated to three sulfur and three nitrogen atoms from three identical ligands in facile trigonal prismatic geometry. The OH group is involved in intramolecular and intermolecular hydrogen bonding. The bound ligands of tris(thiohydrazido)molybdenum(vi) undergo a redox reaction differently depending on the solvents. Two complexes of molybdenum bound to those oxidized ligands were isolated and characterized and their structures were also solved. Of them a binuclear complex, containing two MoO2(2+) ions, of the ligand N-2-hydroxybenzoyl-N'-2-hydroxythiobenzoylhydrazine showed some capability to catalyze the reduction of dinitrogen to ammonia by sodium borohydride.

An oxime based tridentate Schiff base ligand 3-[3-(dimethylamino)propylimino]butan-2-one oxime (HL) produced two dinuclear compounds [Cu2L2(H2O)](ClO4)2 () and [Cu2L2(H2O)](BF4)2 (), and a hexanuclear compound [{Cu3(HL)3(O3ClO)(μ3-O)}2(μ-H)](ClO4)7 () when it was reacted with Cu(ClO4)2·6H2O or Cu(BF4)2·6H2O at different pH values. All three compounds have been structurally and magnetically characterized. Compounds and are dinuclear species in which the two square planar copper(ii) ions are joined solely by the double oximato bridges. On the other hand, the hexanuclear compound consists of two triangular Cu3O cores held together by a proton separated by an OO distance of 2.498(10) Å. The three square pyramidal copper(ii) ions at the corners of an isosceles triangle form a triangular core through central oxido (μ3-O) and peripheral oximato bridges. Each triangular Cu3O core is capped by an unusual triply coordinated (μ3-perchlorato-O,O',O'') perchlorate anion. Variable-temperature (2-300 K) magnetic susceptibility measurements show that compounds exhibit a strong antiferromagnetic interaction with J values -562.6, -633.1 and -636.0 cm(-1) respectively. The X-band EPR data at low temperature clearly indicate the presence of a spin frustration phenomenon in complex .

Biferrocene bearing planar metal dithiocarbamates, namely, [M(FcCH2dtc)2] (dtc = furan-2-ylmethyldithiocarbamate, M = Cu(II) 1, Ni(II) 4; dtc = benzo[d][1,3]dioxol-5-ylmethyl dithiocarbamate, M = Cu(II) 2, Ni(II) 5; dtc = pyridin-2-ylmethyldithiocarbamate, M = Cu(II) 3, Ni(II) 6; Fc = ferrocenyl; Fe(η(5)-C5H5)(η(5)-C5H4-)), have been synthesized and characterized by microanalysis, magnetic susceptibility and cyclic voltammetry. Structures of 1, 2 and 4 have been obtained by single crystal X-ray diffraction. These complexes with pyridyl, piperonyl and furfuryl as heteroaromatic groups in the dithiocarbamate ligands have been exploited as sensitizers in dye sensitized TiO2 solar cells for converting sunlight into electrical energy. Light-to-electrical energy conversion efficiencies achieved using these sensitizers are considerably greater than those obtained with analogous compounds previously reported by us. The overall conversion efficiency (η) is found to be dependent upon the nature of the heteroaromatic conjugated linkers and increases in the order η (ferrocenylfurfuryl) > η (ferrocenylpiperonyl) > η (ferrocenylpyridyl) all values being lower than that obtained in the reference Ru dye N719 under similar experimental conditions. The conversion efficiencies also vary with the metal being higher for Ni (4, 5 and 6) than for Cu complexes (1, 2 and 3). The X-ray structural analyses reveal the existence of rare M···H-C intermolecular anagostic interactions involving the metal atom in chain motifs in 1 and 4, which are retained in solution as evidenced by (1)H NMR spectroscopy.

The trans-[Cu(2)L(2)Cl(2)] (1), and cis-[Cu(2)L(2)Cl(2)]·H(2)O (2) isomers of a diphenoxido bridged Cu(2)O(2) core have been synthesized using a tridentate reduced Schiff base ligand 2-[(2-dimethylamino-ethylamino)-methyl]-phenol. The geometry around Cu(II) is intermediate between square pyramid and trigonal bipyramid (Addison parameter, τ = 0.463) in 1 but nearly square pyramidal (τ = 0.049) in 2. The chloride ions are coordinated to Cu(II) and are trans oriented in 1 but cis oriented in 2. Both isomers have been optimized using density functional theory (DFT) calculations and it is found that the trans isomer is 7.2 kcal mol(-1) more favorable than the cis isomer. However, the hydrogen bonding interaction of crystallized water molecule with chloride ions compensates for the energy difference and stabilizes the cis isomer. Both complexes have been converted to a very rare phenoxido-azido bridged trinuclear species, [Cu(3)L(2)(μ(1,1)-N(3))(2)(H(2)O)(2)(ClO(4))(2)] (3) which has also been characterized structurally. All the complexes are antiferromagnetically coupled but the magnitude of the coupling constants are significantly different (J = -156.60, -652.31, and -31.54 cm(-1) for 1, 2, 3 and respectively). Density functional theory (DFT) calculations have also been performed to gain further insight into the qualitative theoretical interpretation on the overall magnetic behavior of the complexes.

The quadridentate N-heterocyclic ligand 6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2' : 6',2''-terpyridine (CyMe(4)-hemi-BTBP) has been synthesized and its interactions with Am(III), U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UV absorption spectrophotometry, NMR studies and ESI-MS. Structures of 1:1 complexes with Eu(III), Ce(III) and the linear uranyl (UO(2)(2+)) ion were obtained by X-ray crystallographic analysis, and they showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III) complex is higher. (1)H NMR titrations and ESI-MS with lanthanide nitrates showed that the ligand forms only 1:1 complexes with Eu(III), Ce(III) and Yb(III), while both 1:1 and 1:2 complexes were formed with La(III) and Y(III) in acetonitrile. A mixture of isomeric chiral 2:2 helical complexes was formed with Cu(I), with a slight preference (1.4:1) for a single directional isomer. In contrast, a 1:1 complex was observed with the larger Ag(I) ion. The ligand was unable to extract Am(III) or Eu(III) from nitric acid solutions into 1-octanol, except in the presence of a synergist at low acidity. The results show that the presence of two outer 1,2,4-triazine rings is required for the efficient extraction and separation of An(III) from Ln(III) by quadridentate N-donor ligands.

The synthesis and structural characterization of a novel oxoperoxovanadium(V) complex [VO(O(2))(PAH)(phen)] containing the ligands 2-phenylacetohydroxamic acid (PAHH) and 1,10-phenanthroline (phen) has been accomplished. The oxoperoxovanadium(V) complex was found to mimic both vanadate-dependent haloperoxidase (VHPO) activity as well as nuclease activity through effective interaction with DNA. The complex is the first example of a structurally characterized stable oxoperoxovanadium(V) complex with a coordinated bi-dentate hydroximate moiety (-CONHO(-)) from 2-phenylacetohydroximate (PAH). The oxoperoxovanadium(V) complex has been used as catalyst for the peroxidative bromination reaction of some unsaturated alcohols (e.g. 4-pentene-1-ol, 1-octene-3-ol and 9-decene-1-ol) in the presence of H(2)O(2) and KBr. The catalytic products have been characterized by GC-MS analysis and spectrophotometric methods. The DNA binding of this complex has been established with CT DNA whereas the DNA cleavage was demonstrated with plasmid DNA. The interactions of the complex with DNA have been monitored by electronic absorption and fluorescence emission spectroscopy. Viscometric measurements suggest that the compound is a DNA intercalator. The nuclease activity of this complex was confirmed by gel electrophoresis studies.

Facile in situ Cu(II) mediated transformation of p-tolylsulfonyldithiocarbimate in conjunction with polypyridyl or phosphine ligands into corresponding carbamate and thiocarbamate led to the formation of new copper complexes with varying nuclearities and geometries, via C-S bond activation of the ligand within identical reaction systems.

Reaction of a potential NCN-pincer ligand, viz. 1,3-di(phenylazo)benzene (L), with [Rh(PPh(3))(3)Cl] affords, via a C-H bond activation, an interesting dinuclear Rh(II) complex (1), and with RhCl(3)·3H(2)O affords a mononuclear Rh(III) complex (2) containing a catalytically useful Rh-OH(2) fragment.

The preparation, crystal structures and magnetic properties of two new isoelectronic and isomorphous formate- and nitrite-bridged 1D chains of Mn(III)-salen complexes, [Mn(salen)(HCOO)](n) (1) and [Mn(salen)(NO(2))](n) (2), where salen is the dianion of N,N'-bis(salicylidene)-1,2-diaminoethane, are presented. The structures show that the salen ligand coordinates to the four equatorial sites of the metal ion and the formate or nitrite ions coordinate to the axial positions to bridge the Mn(III)-salen units through a syn-antiμ-1κO:2κO' coordination mode. Such a bridging mode is unprecedented in Mn(III) for formate and in any transition metal ion for nitrite. Variable-temperature magnetic susceptibility measurements of complexes 1 and 2 indicate the presence of ferromagnetic exchange interactions with J values of 0.0607 cm(-1) (for 1) and 0.0883 cm(-1) (for 2). The ac measurements indicate negligible frequency dependence for 1 whereas compound 2 exhibits a decrease of χ(ac)' and a concomitant increase of χ(ac)'' on elevating frequency around 2 K. This finding is an indication of slow magnetization reversal characteristic of single-chain magnets or spin-glasses. The μ-nitrito-1κO:2κO' bridge seems to be a potentially superior magnetic coupler to the formate bridge for the construction of single-molecule/-chain magnets as its coupling constant is greater and the χ(ac)' and χ(ac)'' show frequency dependence., (© The Royal Society of Chemistry 2011)

Four new nickel(II) complexes, [Ni(2)L(2)(NO(2))(2)]·CH(2)Cl(2)·C(2)H(5)OH, 2H(2)O (1), [Ni(2)L(2)(DMF)(2)(μ-NO(2))]ClO(4)·DMF (2a), [Ni(2)L(2)(DMF)(2)(μ-NO(2))]ClO(4) (2b) and [Ni(3)L'(2)(μ(3)-NO(2))(2)(CH(2)Cl(2))](n)·1.5H(2)O (3) where HL = 2-[(3-amino-propylimino)-methyl]-phenol, H(2)L(') = 2-({3-[(2-hydroxy-benzylidene)-amino]-propylimino}-methyl)-phenol and DMF = N,N-dimethylformamide, have been synthesized starting with the precursor complex [NiL(2)]·2H(2)O, nickel(ii) perchlorate and sodium nitrite and characterized structurally and magnetically. The structural analyses reveal that in all the complexes, Ni(II) ions possess a distorted octahedral geometry. Complex 1 is a dinuclear di-μ(2)-phenoxo bridged species in which nitrite ion acts as chelating co-ligand. Complexes 2a and 2b also consist of dinuclear entities, but in these two compounds a cis-(μ-nitrito-1κO:2κN) bridge is present in addition to the di-μ(2)-phenoxo bridge. The molecular structures of 2a and 2b are equivalent; they differ only in that 2a contains an additional solvated DMF molecule. Complex 3 is formed by ligand rearrangement and is a one-dimensional polymer in which double phenoxo as well as μ-nitrito-1κO:2κN bridged trinuclear units are linked through a very rare μ(3)-nitrito-1κO:2κN:3κO' bridge. Analysis of variable-temperature magnetic susceptibility data indicates that there is a global weak antiferromagnetic interaction between the nickel(ii) ions in four complexes, with exchange parameters J of -5.26, -11.45, -10.66 and -5.99 cm(-1) for 1, 2a, 2b and 3, respectively.

An uncommon coordination protocol induced by the p-tolylsulfonyl dithiocarbimate ligand (L) [L = p-CH(3)C(6)H(4)SO(2)N[double bond, length as m-dash]CS(2)(2-)] in conjunction with PPh(3) allowed the formation of novel homodimetallic, Cu(2)(PPh(3))(4)L (1), trinuclear heterometallic Cu(2)Ni(L)(2)(PPh(3))(4) (2) and heteroleptic complexes of general formula cis-[M(PPh(3))(2)L] [M = Pd(ii) (3), Pt(ii) (4)]. The complexes have been characterized by microanalysis, mass spectrometry, IR, (1)H, (13)C and (31)P NMR and electronic absorption spectra and single-crystal X-ray crystallography. 2 uniquely consists of square planar, trigonal planar and tetrahedral coordination spheres within the same molecule. In both heteroleptic complexes 3 and 4 the orientation of aromatic protons of PPh(3) ligand towards the Pd(ii) and Pt(ii) center reveals C-HPd and C-HPt rare intramolecular anagostic or preagostic interactions. These complexes exhibit photoluminescent properties in solution at room temperature arising mainly from intraligand charge transfer (ILCT) transitions. The assignment of electronic absorption bands has been corroborated by time dependent density functional theory (TD-DFT) calculations. Complexes 1 and 2 with σ(rt) values ∼ 10(-6) S cm(-1) show semi-conductor properties in the temperature range 313-403 K whereas 3 and 4 exhibit insulating behaviour.

The hexaazamacrocycles [28](DBF)(2)N(6) {cyclo[bis(4,6-dimethyldibenzo[b,d]furaniminoethyleneiminoethylene]} and [32](DBF)(2)N(6) {cyclo[bis(4,6-dimethyldibenzo[b,d]furaniminopropyleneiminopropylene]} form stable dinuclear copper(ii) complexes suitable to behave as receptors for several anionic substrates. These two receptors were used to study the binding interactions with several substrates, such as imidazole (Him) and some carboxylates [benzoate (bz(-)), oxalate (ox(2-)), malonate (mal(2-)), phthalate (ph(2-)), isophthalate (iph(2-)), and terephthalate (tph(2-))] by spectrophotometric titrations and EPR spectroscopy in MeOH (or H(2)O):DMSO (1 : 1 v/v) solution. The largest association constant was found for ox(2-) with Cu(2)[32](DBF)(2)N(6)(4+), whereas for the aromatic dicarboxylate anions the binding constants follow the trend ph(2-) > iph(2-) > tph(2-), i.e. decrease with the increase of the distance of the two binding sites of the substrate. On the other hand, the large blue shift of 68 nm observed by addition of Him to Cu(2)[32](DBF)(2)N(6)(4+) points out for the formation of the bridged CuimCu cascade complex, indicating this receptor as a potential sensor for the detection and determination of imidazole in solution. The X-band EPR spectra of the Cu(2)[28](DBF)(2)N(6)(4+) and Cu(2)[32](DBF)(2)N(6)](4+) complexes and the cascade complexes with the substrates, performed in H(2)O:DMSO (1 : 1 v/v) at 5 to 15 K, showed that the CuCu distance is slightly larger than the one found in crystal state and that this distance increases when the substrate is accommodated between the two copper centres. The crystal structure of [Cu(2)[28](DBF)(2)N(6)(ph)(2)]·CH(3)OH was determined by X-ray diffraction and revealed the two copper centres bridged by two ph(2-) anions at a CuCu distance of 5.419(1) Å. Each copper centre is surrounded by three carboxylate oxygen atoms from two phthalate anions and three contiguous nitrogen atoms of the macrocycle in a pseudo octahedral coordination environment.

Three novel mixed bridged trinuclear and one tetranuclear copper(II) complexes of tridentate NNO donor Schiff base ligands [Cu(3)(L(1))(2)(mu(1,1)-N(3))(2)(CH(3)OH)(2)(BF(4))(2)] (1), [Cu(3)(L(1))(2)(mu(1,1)-N(3))(2)(mu-NO(3)-1kappaO:2kappaO')(2)] (2), [Cu(3)(L(2))(2)(mu(1,1)-N(3))(2)(mu-NO(3)-1kappaO:2kappaO')(2)] (3) and [Cu(4)(L(3))(2)(mu(1,1)-N(3))(4)(mu-CH(3)COO-1kappaO:2kappaO')(2)] (4) have been synthesized by reaction of the respective tridentate ligands (L(1) = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol, L(2) = 2-[1-(2-diethylamino-ethylimino)-ethyl]-phenol, L(3) = 2-[1-(2-dimethylamino-ethylimino)-methyl]-phenol) with the corresponding copper(ii) salts in the presence of NaN(3). The complexes are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. Complex 1 is composed of two terminal [Cu(L(1))(mu(1,1)-N(3))] units connected by a central [Cu(BF(4))(2)] unit through nitrogen atoms of end-on azido ligands and a phenoxo oxygen atom of the tridentate ligand. The structures of 2 and 3 are very similar; the only difference is that the central unit is [Cu(NO(3))(2)] and the nitrate group forms an additional mu-NO(3)-1kappaO:2kappaO' bridge between the terminal and central copper atoms. In complex 4, the central unit is a di-mu(1,1)-N(3) bridged dicopper entity, [Cu(2)(mu(1,1)-N(3))(2)(CH(3)COO)(2)] that connects two terminal [Cu(L(3))(mu(1,1)-N(3))] units through end-on azido, phenoxo oxygen and mu-CH(3)COO-1kappaO:2kappaO' triple bridges to result in a tetranuclear unit. Analyses of variable-temperature magnetic susceptibility data indicates that there is a global weak antiferromagnetic interaction between the copper(II) ions in complexes 1-3, with the exchange parameter J of -9.86, -11.6 and -19.98 cm(-1) for 1-3, respectively. In complex 4 theoretical calculations show the presence of an antiferromagnetic coupling in the triple bridging ligands (acetato, phenoxo and azido) while the interaction through the double end-on azido bridging ligand is strongly ferromagnetic.

The new ligand 6,6''-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2':6',2''-terpyridine (CyMe4-BTTP) has been synthesized in 4 steps from 2,2':6',2''-terpyridine. Detailed NMR and mass spectrometry studies indicate that the ligand forms 1:2 complexes with lanthanide(III) perchlorates where the aliphatic rings are conformationally constrained whereas 1:1 complexes are formed with lanthanide(III) nitrates where the rings are conformationally mobile. An optimized structure of the 1:2 solution complex with Yb(III) was obtained from the relative magnitude of the induced paramagnetic shifts. X-Ray crystallographic structures of the ligand and of its 1:1 complex with Y(III) were also obtained. The NMR and mass spectra of [Pd(CyMe4-BTTP)]n(2n+) are consistent with a dinuclear double helical structure (n = 2). In the absence of a phase-modifier, CyMe4-BTTP in n-octanol showed a maximum distribution coefficient of Am(III) of 0.039 (±20%) and a maximum separation factor of Am(III) over Eu(III) of 12.0 from nitric acid. The metal(III) cations are extracted as the 1:1 complex from nitric acid. The generally low distribution coefficients observed compared with the BTBPs arise because the 1:1 complex of CyMe4-BTTP is considerably less hydrophobic than the 1:2 complexes formed by the BTBPs. In M(BTTP)(3+) complexes, there is a competition between the nitrate ions and the ligand for the complexation of the metal.

Trans-1, [HNEt3][CoIII(LSe)2].H2O and cis-1, [HNEt3][CoIII(LSe)2].3H2O have been synthesized and characterized by single-crystal X-ray studies. The counter ion Et3NH+ plays a crucial role in the crystal packing leading to the formation of two distinctly different supramolecular assemblies in the two complexes. In trans-1, Co-bisphenolate units and triethylamine molecules are arranged in a linear fashion leading to a supramolecular columnar assembly along the crystallographic a-axis. In this assembly, triethylammonium ions are sandwiched between successive Co-bisphenolate units and act as gluing agents joining Co-bisphenolate units on either side through C-Hpi interactions. In sharp contrast to trans-1, Co-bisphenolate units and triethylammonium ions in cis-1 are arranged in a helical supramolecular assembly through similar C-Hpi interactions along the crystallographic b-axis. The SeSe van der Waals interactions may be responsible for the predominant occurrence of the cis- isomer. The cyclic voltammetric studies showed quasi-reversible waves for the cobalt(III)-->cobalt(II) reductions with E1/2=0.635 and 0.628 V vs. Ag/AgCl for cis-1 (at approximately 5 degrees C) and trans-1 (at approximately 25 degrees C), respectively. DFT calculations show that the trans-form is the thermodynamic product with higher stability than the cis- one, which is consistent with the variable temperature 1H NMR studies.

Three new polynuclear copper(II) complexes of singly deprotonated L-glutamic acid (L-glu), {[Cu(bipy)2][Cu(bipy)(L-glu)H2O]2(BF4)4 x (H2O)3}n (1), {[Cu(bipy)(L-glu)H2O][Cu(bipy)(L-glu)(ClO4)](ClO4) x (H2O)2}n (2) and [Cu(phen)(L-glu)H2O]2(NO3)2 x (H2O)4 (3) (bipy = 2,2-bipyridine, phen = 1,10-phenanthroline), were synthesized in acidic pH (ca. 2.5) and characterized structurally. In all the complexes, L-glutamic acid acts as a bidentate chelating ligand, leaving the protonated carboxylic acid free. Both in 1 and 2, two different types of species [Cu(bipy)2](BF4)2 and [Cu(bipy)(L-glu)H2O]BF4 for 1 and [Cu(bipy)(L-glu)H2O]ClO4 and [Cu(bipy)(L-glu)(ClO4)] for 2 coexist in the solid state. In complex 1, the [Cu(bipy)(L-glu)H2O]+ units are joined together by syn-anti carboxylate bridges to form an enantiopure (M) helical chain and the [Cu(bipy)2]2+ presents a very rare example of the four-coordinate distorted tetrahedral geometry of Cu(II). In complex 2, the [Cu(bipy)(L-glu)(ClO4)] units are joined together by weakly coordinating perchlorate ions to form a 1D polymeric chain while the [Cu(bipy)(L-glu)H2O]+ units remain as mononuclear species. The different coordinating ability of the two counter anions along with their involvement in the H-bonding network seems likely to be responsible for the difference in the final polymeric structures in the two compounds. Variable-temperature (2-300 K) magnetic susceptibility measurements show negligible coupling for both the complexes. The structure of 3 consists of two independent monomeric [Cu(phen)(L-glu)H2O]+ cations, two nitrate anions and four water molecules. The copper atom occupies a five-coordinate square pyramidal environment with a water molecule in the axial position.

This article describes the synthesis and anion binding properties of a series of 'picket fence' metalloporphyrin complexes, within which the metal centre is systematically varied. The porphyrin structure contains four amide bonds and is the same for each metal. The anion binding properties of these receptors are further contrasted with those of their tetraphenylporphyrin congeners to elucidate both the effect of the metal centre and the influence of the amide groups on the anion recognition process. Anion binding was demonstrated using UV/visible and (1)H NMR spectroscopies, electrochemistry and luminescence. The metal centre was found to be highly influential in the strength and selectivity of binding; for example, the cadmium and mercury complexes exhibited far greater affinities for anions than the zinc complexes in competitive solvents such as DMSO. The amide functionalities were found to enhance the anion binding process.

The ligands 1,4,8,11-tetraazacyclotetradecane-1,4,8-triacetic-11-methylphosphonic acid (H5te3a1p) and 1,4,8,11-tetraazacyclotetradecane-1,4,8-triacetic acid (H3te3a) were synthesized, the former one for the first time. The syntheses of these ligands were achieved from reactions on 1,4,8,11-tetraazacyclotetradecane-1,4,8-tris(carbamoylmethyl) hydroiodide (te3am x HI), and compounds (Hte3am)+, 1, and (H7te3a1p)2+, 4, were characterized by X-ray diffraction. Structures of two other compounds resulting from side-reactions, (H2te2lac)2+, 2, and (H4te2a2pOEt2)2+, 4, were also determined by X-ray diffraction. Potentiometric titrations of H5te3a1p and H3te3a were performed at 298.2 K and ionic strength 0.10 mol dm(-3) in NMe4NO3 to determine their protonation constants. 1H and 31P NMR titrations of H5te3a1p were carried out in order to determine the very high first protonation constant of this ligand and to elucidate the sequence of protonation. Potentiometric studies of the two ligands with Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ metal ions performed in the same experimental conditions showed that the complexes of H5te3a1p present very high thermodynamic stability while complexes of H3te3a, particularly Co2+ and Zn2+, are even more stable. 31P NMR spectra of the cadmium(II) complex of H5te3a1p showed that the phosphonate moiety was coordinated to the metal ion. The UV-vis-NIR spectroscopic data and magnetic moment values of Co2+ and Ni2+ complexes of H5te3a1p and H3te3a together with the EPR of the corresponding Cu2+ complexes indicated that all these complexes adopt distorted octahedral coordination geometries in solution. This was confirmed by the single crystal structure of [Cu2(Hte3a)(H2O)3Cl]Cl0.5(ClO4)0.5 x 2H2O that showed two distorted octahedral copper centres bridged by a N-acetate pendant arm with a CuCu distance of 4.890(1) A. The first one is encapsulated into the macrocyclic cavity surrounded by four nitrogen and two oxygen donors from the macrocycle, whereas the second one is on the periphery of the macrocycle and is coordinated to two oxygen atoms of one acetate pendant arm in chelating fashion, one chloride and three water molecules.

Reaction of cis-Ru(bisox)(2)Cl(2), where bisox is 4,4,4',4'-tetramethyl-2,2'-bisoxazoline, with HNO(3) in 1 : 4 molar proportion in boiling water under N(2) atmosphere and subsequent addition of an excess of NaClO(4).H(2)O yields [Ru(bisox)(HL)(NO)](ClO(4))(NO(3)) (1). HL is a hydrolysed form of bisox where one of the oxazoline rings opens up. X-Ray crystallography shows that 1 contains an octahedral RuN(5)O core. HL binds the metal through an imino N, an amide N and an alcoholic O atom. Reaction of cis-Ru(bisox)(2)Cl(2) with an excess of NaNO(2) in water gives cis-Ru(bisox)(2)(NO(2))(2) (2). On acidification by HClO(4) in methanol, is smoothly converted to cis-[Ru(bisox)(2)(NO(2))(NO)](ClO(4))(2) (3) due to equilibrium (1). [Formula: see text] (1) The X-ray crystal structures of 2 and 3 have also been determined. NO binds Ru in 1 and 3 linearly. The Ru-NO bond length in 1 is 1.764(13) A and that in 3 is approximately 1.78 A. All the three complexes have been characterised by FTIR, NMR and ESIMS. The NO stretching frequencies in 1 and 3 are 1897 and 1936 cm(-1) respectively. While 3 reverts back to 2 readily in presence of OH(-) [equilibrium (1)], 1 does not react with OH(-). It is concluded that while in the reaction of cis-Ru(bisox)(2)Cl(2) with HNO(3), bisox is hydrolysed following abstraction of NO from HNO(3), generation of the nitrosyl complex 3 via reaction (1) is not accompanied with such hydrolysis.

Cyclo-condensation of aroyl hydrazides with the cationic tungsten-dichlorodiazomethane complex [BrW(dppe)2(N2CCl2)]+ affords neutral oxadiazolyldiazenido(1-) complexes which react readily with a wide range of transition and non-transition metal species to afford a novel series of crystallographically-characterised heteropolynuclear complexes containing bridging oxadiazolyldiazenido(1-) ligands.

Extended-chain complexes containing multiple transition metal centres linked by conjugated micro-cyanodiazenido(1-) ligands [N=N-C[triple bond, length as m-dash]N]- have been obtained by reaction of trans-[BrW(dppe)2(N2CN)], , [dppe=1,2-bis(diphenylphosphino)ethane] with dirhodium(II) tetra-acetate, bis(benzonitrile)palladium(II) dichloride, and bis(aqua)M(II) bis(hexafluoroacetylacetonate) (M=Mn, Ni, Cu, Zn): stronger Lewis acids such as tetrakis(acetonitrile)palladium(II) tetrafluoroborate and boron trifluoride promote hydrolysis of complex , leading to the isolation of a novel carbamoylhydrazido(2-) complex, trans-[BrW(dppe)2(N2HC=ONH2)]+[BF4]-.

A novel single thiocyanato-bridged one-dimensional polymer, [NiL(NCS)(micro-NCS)]n (L = N1-(1-pyridin-2-yl-ethylidine)propane-1,3-diamine) has been synthesized and characterized by X-ray crystallography and a variable temperature magnetic study; the compound is a metamagnet with a Neél temperature (T(N)) of 3.5 K.

The new dioxatetraazamacrocycle (L1) was synthesized by a 2 + 2 condensation and characterized. Stability constants of its copper(II) complexes were determined by spectrophotometry in DMSO at 298.2 K in 0.10 mol dm(-3) KClO4. Mainly dinuclear complexes are formed and the presence of mononuclear species is dependent on the counterion (Cl- or ClO4-). The association constants of the dinuclear copper(II) complexes with dicarboxylate anions [oxalate (oxa(2-)), malonate (mal(2-)), succinate (suc(2-)), and glutarate (glu(2-))] were also determined by spectrophotometry at 298.2 K in DMSO, and it was found that values decrease with an increase of the alkyl chain between the carboxylate groups. X-Band EPR spectra of the dicopper(II) complexes and of their cascade species in frozen DMSO exhibit dipole-dipole coupling, and their simulation, together with their UV-vis spectra, showed that the copper centres of the complexes in solution had square pyramidal geometries though with different distortions. From the experimental data, it was also possible to predict the Cu...Cu distances, the minimum being found at 6.4 angstroms for the Cu2L1Cl4 complex and then successively this distance slightly increases when the chloride anions are replaced by dicarboxylate anions, from 6.6 angstroms for oxa(2-) to 7.8 angstroms for glu(2-). The crystal structures of the dinuclear copper cascade species with oxa(-2) and suc(2-) were determined and showed one anion bridging both copper centres and Cu...Cu distances of 5.485(7) angstroms and 6.442(8) angstroms, respectively.

New dioxadiaza- and trioxadiaza-macrocycles containing one rigid dibenzofuran unit (DBF) and N-(2-aminoethyl) pendant arms were synthesized, N,N'-bis(2-aminoethyl)-[17](DBF)N(2)O(2) (L(1)) and N,N'-bis(2-aminoethyl)-[22](DBF)N(2)O(3) (L(2)), respectively. The binding properties of both macrocycles to metal ions and structural studies of their metal complexes were carried out. The protonation constants of both compounds and the stability constants of their complexes with Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Pb(2+) were determined at 298.2 K, in aqueous solutions, and at ionic strength 0.10 mol dm(-3) in KNO(3). Mononuclear complexes with both ligands were formed, and dinuclear complexes were only found for L(2). The thermodynamic binding affinities of the metal complexes of L(2) are lower than those of L(1) as expected, but the Pb(2+) complexes of both macrocycles exhibit close stability constant values. On the other hand, the binding affinities of Cd(2+) and Pb(2+) for L(1) are very high, when compared to those of Co(2+), Ni(2+) and Zn(2+). These interesting properties were explained by the presence of the rigid DBF moiety in the backbone of the macrocycle and to the special match between the macrocyclic cavity size and the studied larger metal ions. To elucidate the adopted structures of complexes in solution, the nickel(II) and copper(II) complexes with both ligands were further studied by UV-vis-NIR spectroscopy in DMSO-H(2)O 1 : 1 (v/v) solution. The copper(II) complexes were also studied by EPR spectroscopy in the same mixture of solvents. The crystal structure of the copper complex of L(1) was also determined. The copper(II) displays an octahedral geometry, the four nitrogen atoms forming the equatorial plane and two oxygen atoms, one from the DBF unit and the other one from the ether oxygen, in axial positions. One of the ether oxygens of the macrocycle is out of the coordination sphere. Our results led us to suggest that this geometry is also adopted by the Co(2+) to Zn(2+) complexes, and only the larger Cd(2+) and Pb(2+) manage to form complexes with the involvement of all the oxygen atoms of the macrocyclic backbone.

The binding properties of dioxadiaza- ([17](DBF)N2O2) and trioxadiaza- ([22](DBF)N2O3), macrocyclic ligands containing a rigid dibenzofuran group (DBF), to metal cations and structural studies of their metal complexes have been carried out. The protonation constants of these two ligands and the stability constants of their complexes with Ca2+, Ba2+, and Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+, were determined at 298.2 K in methanol-water (1:1, v/v), and at ionic strength 0.10 mol dm-3 in KNO3. The values of the protonation constants of both ligands are similar, indicating that no cavity size effect is observed. Only mononuclear complexes of these ligands with the divalent metal ions studied were found, and their stability constants are lower than expected, especially for the complexes of the macrocycle with smaller cavity size. However, the Cd2+ complex with [17](DBF)N2O2 exhibits the highest value of stability constant for the whole series of metal ions studied, indicating that this ligand reveals a remarkable selectivity for cadmium(II) in the presence of all the metal ions studied, except copper(II), indicating that this ligand reveals a remarkable selectivity for cadmium(II) in the presence of the mentioned metal ions. The crystal structures of H2[17](DBF)N2O3(2+) (diprotonated form of the ligand) and of its cadmium complex were determined by X-ray diffraction. The Cd2+ ion fits exactly inside the macrocyclic cavity exhibiting coordination number eight by coordination to all the donor atoms of the ligand, and additionally to two oxygen atoms from one nitrate anion and one oxygen atom from a water molecule. The nickel(II) and copper(II) complexes with the two ligands were further studied by UV-vis-NIR and the copper(II) complexes also by EPR spectroscopic techniques in solution indicating square-pyramidal structures and suggesting that only one nitrogen and oxygen donors of the ligands are bound to the metal. However an additional weak interaction of the second nitrogen cannot be ruled out.

New N-(3-aminopropyl) (L1, L2) and (2-cyanoethyl) (L3, L4) derivatives of a 14-membered tetraazamacrocycle containing pyridine have been synthesized. The protonation constants of L1 and L2 and the stability constants of their complexes with Ni2+, Cu2+, Zn2+ and Cd2+ metal ions were determined in aqueous solutions by potentiometry, at 298.2 K and ionic strength 0.10 mol dm(-3) in KNO3. Both compounds have high overall basicity due to the presence of the aminopropyl arms. Their copper(II) complexes exhibit very high stability constants, which sharply decrease for the complexes of the other studied metal ions, as usually happens with polyamine ligands. Mono- and dinuclear complexes are formed with L2 as well as with L1, but the latter exhibits mononuclear complexes with slightly higher K(ML) values while the dinuclear complexes of L2 are thermodynamically more stable. The presence of these species in solution was supported by UV-VIS-NIR and EPR spectroscopic data. The single crystal structures of [Cu(H2L2)(ClO4)]3+ and [CoL3Cl]+ revealed that the metal centres are surrounded by the four nitrogen atoms of the macrocycle and one monodentate ligand, adopting distorted square pyramidal geometries. In the [CoL3Cl]+ complex, the macrocycle adopts a folded arrangement with the nitrogen atom opposite to the pyridine at the axial position while in the [Cu(H2L2)(ClO4)]3+ complex, the macrocycle adopts a planar conformation with the three aminopropyl arms located at the same side of the macrocyclic plane.

New hydrophobic, tetradentate nitrogen heterocyclic reagents, 6,6'-bis-(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2'-bipyridines (BTBPs) have been synthesised. These reagents form complexes with lanthanides and crystal structures with 11 different lanthanides have been determined. The majority of the structures show the lanthanide to be 10-coordinate with stoichiometry [Ln(BTBP)(NO3)3] although Yb and Lu are 9-coordinate in complexes with stoichiometry [Ln(BTBP)(NO3)2(H2O)](NO3). In these complexes the BTBP ligands are tetradentate and planar with donor nitrogens mutually cisi.e. in the cis, cis, cis conformation. Crystal structures of two free molecules, namely C2-BTBP and CyMe4-BTBP have also been determined and show different conformations described as cis, trans, cis and trans, trans, trans respectively. A NMR titration between lanthanum nitrate and C5-BTBP showed that two different complexes are to be found in solution, namely [La(C5-BTBP)2]3+ and [La(C5-BTBP)(NO3)3]. The BTBPs dissolved in octanol were able to extract Am(III) and Eu(III) from 1 M nitric acid with large separation factors.

A tetraazamacrocycle containing ferrocene moieties has been synthesized and characterized. The tetraprotonated form of this compound was evaluated as a receptor (R) for anion recognition of several substrates (S), Cl(-), PF(6)(-), HSO(4)(-), H(2)PO(4)(-) and carboxylates, such as p-nitrobenzoate (p-nbz(-)), phthalate (ph(2-)), isophthalate (iph(2-)) and dipicolinate (dipic(2-)). (1)H NMR titrations in CD(3)OD indicated that this receptor is not suitable for recognizing HSO(4)(-) and H(2)PO(4)(-), but weakly binds p-nbz(-), and strongly interacts with ph(2-), dipic(2-), and iph(2-) anions forming 1 : 2 assembled species. The largest beta(2) binding constant was determined for ph(2-), followed by dipic(2-) and finally iph(2-). The effect of the anionic substrates on the electron-transfer process of the ferrocene units of R was evaluated using cyclic voltammetry (CV) and square wave voltammetry (SWV) in methanol solution and 0.1 mol dm(-3)(CH(3))(4)NCl as the supporting electrolyte. Titrations of the receptor were undertaken by addition of anion solutions in their tetrabutylammonium or tetramethylammonium forms. The protonated ligand exhibits a reversible voltammogram, which shifts cathodically in the presence of the substrates. The data revealed kinetic constraints in the formation of the receptor/substrate entity for dipic(2-), ph(2-) and iph(2-) anions, but not for p-nbz(-). In spite of the slow kinetics of assembled species formation with the ph(2-) substrate, this anion provides the largest redox-response when the supramolecular entity is formed, followed by dipic(2-), iph(2-) and finally p-nbz(-) anions. This trend is in agreement with the (1)H NMR results and the values of the binding constants. Single crystal X-ray structures of the receptor with PF(6)(-), ph(2-), iph(2-) and p-nbz(-) were carried out and showed that supermolecules with a RS(2) stoichiometry are formed with the first three anions, but RS(4) with p-nbz(-). In all cases the binding occurs outside the macrocyclic cavity via N-H...O=C hydrogen bonds for carboxylate anions and N-H...F hydrogen bonds for the PF(6)(-) anion, which is in agreement with the solution results. The macrocyclic framework adopts different conformations in order to interact with each substrate having Fe...Fe intramolecular distances ranging from 10.125(14) to 12.783(15)A.

The previously synthesised Schiff-base ligands 2-(2-Ph(2)PC(6)H(4)N[double bond, length as m-dash]CH)-R'-C(6)H(3)OH (R'= 3-OCH(3), HL(1); 5-OCH(3), HL(2); 5-Br, HL(3); 5-Cl, HL(4)) were prepared by a faster, more efficient route involving a microwave assisted co-condensation of 2-(diphenylphosphino)aniline with the appropriate substituted salicylaldehyde. HL(1-4) react directly with M(II)Cl(2)(M = Pd, Pt) or Pt(II)I(2)(cod) affording neutral square-planar complexes of general formula [M(II)Cl(eta(3)-L(1-4))](M = Pd, Pt, 1-8) and [Pt(II)I(eta(3)-L(1-4))](M = Pd, Pt, 9-12). Reaction of complexes 1-4 with the triarylphosphines PR(3)(R = Ph, p-tolyl) gave the novel ionic complexes [Pd(II)(PR(3))(eta(3)-L(1-4))]ClO(4)(13-20). Substituted platinum complexes of the type [Pt(II)(PR(3))(eta(3)-L(1-4))]ClO(4)(R = P(CH(2)CH(2)CN)(3)21-24) and [Pt(II)(P(p-tolyl)(3))(eta(3)-L(3,4))]ClO(4)( 25 and 26 ) were synthesised from the appropriate [Pt(II)Cl(eta(3)-L(1-4))] complex (5-8) and PR(3). The complexes are characterised by microanalytical and spectroscopic techniques. The crystal structures of 3, 6, 10, 15, 20 and 26 were determined and revealed the metal to be in a square-planar four-coordinate environment containing a planar tridentate ligand with an O,N,P donor set together with one further atom which is trans to the central nitrogen atom.

The synthesis of a range of ditopic polyferrocenyl zinc(II) dithiocarbamate macrocyclic receptors containing ferrocene groups on the macrocycle's periphery and/or as part of the cyclic cavity is reported. The assemblies have been characterised by a range of spectroscopic techniques, electrochemical studies and in two cases by X-ray structure determination. The ability of these host systems to bind and sense electrochemically anionic guest species, isonicotinate and benzoate, and neutral 4-picoline guest was examined by 1H NMR and cyclic voltammetric titration studies. The strongest association was found between the isonicotinate anion and a dinuclear zinc(II) receptor whose macrocyclic cavity is of complementary size to complex this bidentate guest species in a cooperative manner. Cyclic voltammetric studies demonstrated that all receptors can electrochemically sense the binding of isonicotinate and benzoate via significant cathodic perturbations of the respective ferrocene redox couple.