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In this work, the structural and spectroscopic characterization of trans-[Ni{(OPPh2)(EPPh2)N)}2(dmso)2], E = S, Se, complexes is described. These Ni(II) complexes contain two chelating (O,E) = [(OPPh2)(EPPh2)N)]− ligands, as well as two dimethyl sulfoxide (dmso) molecules coordinated via their O atoms. X-ray crystallography studies revealed a highly anisotropic pseudo-octahedral trans-NiO4E2 coordination environment, extending the literature dataset of their trans-[Ni(O,E)2(sol)2], sol = dmf, thf, counterparts. Collectively considered, these six complexes contain similar coordination spheres, exhibiting, however, subtle structural differences due to the nature of the donor atom (E) and solvent molecule (sol) coordinated to Ni(II). The spin Hamiltonian parameters of S = 1 trans-[Ni(O,Se)2(dmso)2], E = S, Se, were accurately determined by high-frequency and -field EPR spectroscopy, applying a methodology already used for trans-[Ni(O,E)2(sol)2], sol = dmf, thf. Magnetostructural correlations are explored between all members of this sub-family of Ni(II) complexes.

This work focuses on the development of “2 + 1” technetium and rhenium carbonyl complexes of the formula fac-[99mTc/Re(CO)3(L)(Spy)], where HSpy is 2-mercaptopyridine and acts as (NS) bidentate ligand and L is either triphenylphosphine (PPh3) or benzyl isocyanide (BnNC). Reaction of 2-mercaptopyridine with the precursors fac-(NEt4)2[Re(CO)3Br3] or [Re(CO)5Br] yields the dimeric complex fac-[Re(CO)3(Spy)]2, Re1. Re1 readily reacts with the monodentate ligand to yield the respective “2 + 1” fac-[Re(CO)3(PPh3/BnNC)(Spy)] complexes Re2/Re4. Re2 was also obtained in a single step reaction of the precursor fac-(NEt4)2[Re(CO)3Br3] with the mixture of ligands in equimolar amounts. Furthermore, the rhenium dicarbonyl complex cis, trans-[Re(CO)2(PPh3)2(Spy)] complex Re3 was synthesized by reaction of HSpy with the precursor mer, trans-[Re(CO)3(PPh3)2Cl]. All rhenium complexes were characterized by IR, NMR, elemental analysis and furthermore the structure of Re1, Re2, Re3 was solved by X-ray crystallography. At the 99mTc tracer level, the “2 + 1” complex fac-[99mTc(CO)3(PPh3)(Spy)], 99mTc2, was obtained in high radiochemical yield and low ligand concentrations and the complex was very stable in histidine and cysteine in challenge experiments.

The study of the general reaction system Co(NO3)2·6H2O/Ln(NO3)3·6H2O (Ln = Tb, Dy, Ho, Er)/2-pyridinealdoxime (paoH)/Bun4NOH in MeCN under aerobic conditions provided access to fac-[CoIII(pao)3] (4). Starting from Co(II) sources, i.e. in the absence of LnIII ions, the known [Polyhedron 28 (2009) 1638] mer diastereoisomer, mer-[CoIII(pao)3] (3), could only be isolated. The crystallization of 4 is probably due to the formation of a mixed CoIII/LnIII species in solution, which already possesses the fac-{CoIII(pao)3} unit. The fac isomer 4 is converted readily to the mer-isomer 3, while the opposite transformation was not achieved under the reaction conditions employed. Complex [CoIII(pao)2(paoH)](ClO4) (5) was prepared in good yield from the aerobic reaction of Co(ClO4)2·6H2O and excess of paoH in MeOH. Treatment of 5 in MeCN/MeOH with one equivalent of base gives 3. The structures of the new complexes 4·MeCN and 5 have been determined by single-crystal X-ray crystallography. The distorted octahedral CoIII ion in 4 is coordinated by three N,N′-bidentate chelating ligands; the molecule is the facial diastereoisomer. The distorted octahedral CoIII center in the cation of 5 is coordinated by four nitrogen atoms of two pao− ligands and two nitrogen atoms of one neutral paoH molecule; the disposition of the donor atoms around the metal center is meridional. The cations [CoIII(pao)2(paoH)]+ form centrosymmetric dimers in the crystal lattice as a consequence of O(oxime)–H⋯O− (oximate) H bonds; the dimers form tetramers through weak C(oxime)–H⋯O(oxime) H-bonding interactions. Metric parameters show that the deprotonated oximato group of the pao− ligands in 4·MeCN and 5 is better described as . Solid-state UV–Vis and IR data are discussed in terms of the low-spin octahedral stereochemistry of CoIII and the nature of bonding, respectively. The 1NMR spectrum of 4·MeCN in CDCl3 provides strong evidence of the fac → mer transformation in solution.

In this work, we focused on the development of mixed ligand technetium and rhenium complexes of the general formula fac-[99mTc/Re(CO)3(PPh3)(ox/tq)] and cis, trans-[99mTc/Re(CO)2(PPh3)2(ox/tq)] where 8-hydroxyquinoline (oxH) and 8-mercaptoquinoline (tqH) act as [NO] and [NS] bidentate ligands. The synthesis of rhenium complexes fac-[Re(CO)3(PPh3)(ox/tq)] Re3/Re4 was conducted by reacting oxH or tqH and triphenylphosphine with fac-(NEt4)2[Re(CO)3Br3] (1) or by reacting triphenylphosphine with the dimer complexes fac-[Re(CO)3(ox/tq)]2 Re1/Re2. The synthesis of the rhenium complexes cis, trans-[Re(CO)2(PPh3)2(ox/tq)] Re5/Re6 was conducted either by reacting 1 with oxH/tqH in equimolar amounts and triphenylphosphine in excess or by reacting oxH/tqH with the precursor mer, trans-[Re(CO)3(PPh3)2Cl]. All the complexes were characterized by IR, NMR and X-ray crystallography. The analogous 99mTc complexes were prepared by reacting oxH/tqH and PPh3 with the precursor fac-[99mTc(CO)3(OH2)3]+ (2). When the reaction mixture was left at rt for 2 h the monophosphino complexes fac-[99mTc(CO)3(PPh3)(ox/tq)] 99mTc3/99mTc4 were formed, while by applying heating at 75 °C for 30 min the dicarbonyl complexes cis, trans-[99mTc(CO)2(PPh3)2(ox/tq)] 99mTc5/99mTc6 were formed quantitatively. The 99mTc complexes were identified by HPLC chromatographic comparison with the analogous rhenium complexes and their stability was studied.

Reactions of copper(II) sources with 1,2-bis(4-pyridyl)ethane (bpe) yielded metal–organic networks with diverse topologies and dimensionalities. Compounds [Cu(bpe)2(dmf)2]n(ClO4)2n·2ndmf (1·2ndmf), [Cu(bpe)2(dmf)2]n(ClO4)2n·3.5ndmf (2·3.5ndmf), [Cu(bpe)2(NO3)2]n·2nH2O (4·2nH2O) and [Cu2(bpe)(O2CMe)4]n·0.7nH2O (5·0.7nH2O) have been isolated by altering the copper(II) source, the reaction solvent and the crystallization process. Compounds 1·2ndmf and 2·3.5ndmf consist of cationic [Cu(bpe)2(dmf)2]2+ repeating units assembled to 1D and 2D (4,4) networks, respectively, and represent supramolecular isomers due to the conformational isomerism of the bridging bpe molecules. Compound 4·2nH2O consists of neutral mononuclear [Cu(dpe)2(NO3)2] repeating units assembled to inclined interpenetrating (4,4) sheets describing an overall entanglement that is 3D in nature, and compound 5·0.7nH2O consists of neutral dinuclear repeating units assembled to cross-linked 1D chains.

The initial employment of N,N-bis(2-hydroxyethyl)glycine (bicine; bicH3) in CdCl2 chemistry is reported, and the syntheses, IR spectra and crystal structures of the 1D coordination polymers [CdCl(bicH2)]n·nH2O (1·H2O) and [CdNaCl2(bicH2)(MeOH)]n (2) are described. The identity of the products depends on the solvent, the reaction temperature and the alkali metal ion of the base used. The structure of 1·H2O consists of zig-zag chains. The 7-coordinate CdII atoms are bridged by η1:η1:μ2 carboxylate groups of the 2.21111 (Harris notation) bicH2− ligand. The coordination geometry of the metal center can be either described as a very distorted pentagonal bipyramidal or as a distorted capped octahedral. In the structure of 2 the CdII atoms form an almost linear chain with neighboring NaI atoms on opposite sites of the chain. Every pair of CdII atoms is linked by two chloro ligands and the two oxygen atoms of the bicinate carboxylate group. The CdII and NaI atoms are bridged by one μ2 carboxylate bicinate oxygen and one μ3 chloro ligand. The 3.21,211121212 coordination mode of bicH2− is unprecedented. The CdCl4(Ocarboxylate)2 and Na(Ohydroxyl)2(Ocarboxylate)(OMeOH)NCl coordination spheres are octahedral and trigonal prismatic, respectively. IR data of the complexes are discussed in terms of the coordination modes of bicH2− and the known structures.

Reactions of malonic acid (H2mal) with PrCl3·6H2O afforded the known complex [Pr2(mal)3(H2O)6]n (1), and compounds [Pr2(mal)3(H2O)6]n·2nH2O (2·2nH2O), [PrCl(mal)(H2O)3]n·0.5nH2O (3·0.5nH2O) and [Pr(mal)(Hmal)(H2O)3]n·nH2O (4·nH2O) using various reaction ratios, reaction media (H2O, MeOH) and pH values. Analogous reactions with CeCl3·7H2O afforded compounds [Ce2(mal)3(H2O)6]n (5), [CeCl(mal)(H2O)3]n·nH2O (6·nH2O) and [Ce(mal)(Hmal)(H2O)3]n·nH2O (7·nH2O). Compounds 2·2nH2O and 3·0.5nH2O were characterized by X-ray crystallography, and 4–7 by microanalytical and spectroscopic data. The malonate(-2) ligand adopts three different coordination modes in the structures of 1–3, i.e., the μ2-κO:κO′:κO″ and the μ4-κ2O:κO′:κ2O″:κO‴ in 1 and 2 leading to a 3D network structure, and the μ3-κ2O:κO′:κ2O″:κO‴ in 3 promoting an 1D structure. The thermal decomposition of 1 and 3·0.5nH2O was monitored by TG/DTA and TG/DTG measurements. The structural features of 1–3 are discussed in terms of known malonato(-2) LnIII and CaII complexes. The bioinorganic chemistry relevance of our results is discussed.

A bioinorganic approach into the problem of the isomorphous substitution of calcium(II) by lanthanide(III) ions in biological systems is discussed. Reactions of malonamic acid (H2malm) with CaII and NdIII sources under similar conditions yielded the compounds [Ca(Hmalm)2]n (1), [Nd(Hmalm)2(H2O)2]n(NO3)n (2) and [Nd(Hmalm)2(H2O)2]nCln·2nH2O (3·2nH2O). Their X-ray crystal structure data show that the malonamate(-1) ligand presents two different ligation modes and coordinates through the two carboxylate and the amide-O atoms, thus bridging three CaII ions in 1 and two NdIII ions in 2 and 3·2nH2O. Complex 1 is a 3D coordination polymer based on neutral repeating units, whereas 2 and 3·2nH2O are 1D coordination polymers based on the same cationic repeating unit. Hydrogen bonding interactions further stabilize the 3D framework structure of 1 and assemble the 1D chains of 2 and 3·2nH2O into 3D networks. The three complexes were characterized spectroscopically (IR, far-IR, and Raman) and the thermal decomposition of 2 and 3·2nH2O was monitored by TG/DTA and TG/DTG measurements. Variable-temperature magnetic susceptibility data for 2 are also reported. The bioinorganic chemistry relevance of our results is discussed.

The reaction of succinamic acid (H2sucm) with Ca(NO3)2·4H2O yielded compounds [Ca(Hsucm)(NO3)(H2O)]n (1) and [Ca(Hsucm)2]n (2). The succinamate(-1) ligand presents two new ligation modes and coordinates through the two carboxylato and the amide O-atoms, thus bridging three CaII ions which assemble into zig-zag 1D chains in 1 and 2D networks in 2. Intermolecular hydrogen bonding interactions in the crystal structures of 1 and 2 result in overall 3D framework structures. Both compounds have been characterized by IR and 1H NMR spectroscopy, and their thermal decomposition was monitored by TG/DTG and DSC measurements. The structural comparison of 1 and 2 with known lanthanide(III) succinamate(-1) complexes reveals differences in the coordination mode of the ligand and in the coordination number of the metal ions; the biological relevance of these differences is discussed.

The use of succinamic acid (H2sucm) in CuII/N,N′,N″-donor [2,2′:6′,2″-terpyridine (terpy), 2,6-bis(3,5-dimethylpyrazol-1-yl)pyridine (dmbppy)] reaction mixtures yielded compounds [Cu(Hsucm)(terpy)]n(ClO4)n (1), [Cu(Hsucm)(terpy)(MeOH)](ClO4) (2), [Cu2(Hsucm)2(terpy)2](ClO4)2 (3), [Cu(ClO4)2(terpy)(MeOH)] (4), [Cu(Hsucm)(dmbppy)]n(NO3)n·3nH2O (5.3nH2O), and [CuCl2(dmbppy)]·H2O (6·H2O). The succinamate(−1) ligand exists in four different coordination modes in the structures of 1–3 and 5, i.e., the μ2-κO:κO′:κO″ in 1 and 5 which involves asymmetric chelating coordination of the carboxylato group and ligation of the amide O-atom leading to 1D coordination polymers, the μ2-κ2O:κO′ in 3 which involves asymmetric chelating and bridging coordination of the carboxylato group, and the asymmetric chelating mode in 2. The primary amide group, either coordinated in 1 and 5, or uncoordinated in 2 and 3, participate in hydrogen bonding interactions, leading to interesting crystal structures. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the Hsucm− ligands. The thermal decomposition of complex 5·3nH2O was monitored by TG/DTG and DTA measurements.

The unsymmetrical nickel 1,2-dithiolene complex based on diphenylethylenedithiolate (dpedt) and 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate (pddt) was prepared and characterized. Depending on the conditions of crystallization, it is possible to obtain the complex in two different crystalline forms. X-ray structure studies recognize these forms as Ni(dpedt)(pddt) and Ni(dpedt)(pddt)·CS2. The experimental optical and electrochemical parameters are in a good agreement with the calculated ones, using the corresponding parameters of the symmetrical complexes, Ni(dpedt)2 and Ni(pddt)2. The HOMO and LUMO energy levels, obtained from optical and electrochemical measurements, are very close to the Fermi energy of (metallic) Au. The chemical and electrochemical properties of both forms showed that they are stable in air and could be candidate materials for optics and electronics.

The synthesis and structural characterization of the neutral rhenium complex fac-[Re(NSO)(CO)3], Re-1, where (NSO) is a tridentate bifunctional chelating agent, 3-(carboxymethylthio)-3-(1H-imidazol-4-yl)propanoic acid (1), is presented. The complex crystallized from methanol–water and its structure was assigned by IR and 1H, 13C NMR spectroscopies and X-ray crystallography. Furthermore, the analogous technetium complex fac-[99mTc(NSO)(CO)3], 99mTc-1, was synthesized in high yield by reacting ligand 1 with the fac-[99mTc(OH2)3(CO)3]+ precursor for 30 min at 85 °C. The tracer complex was found to be more than 95% stable in the L-histidine challenge experiment. Our data indicate that the bifunctional NSO chelating agent 1 can be successfully applied for the development of potential 99mTc-radiopharmaceuticals.

The use of succinamic acid (H 2 sucm)/N,N′-chelate (2,2′-bipyridine, bpy; 4,4′-dimethyl-2,2′-bipyridine, dmbpy; 1,10-phenanthroline, phen) ‘ligand blends’ in CuX 2 · y H 2 O (X = NO 3 , y = 3; X = Cl, y = 0) chemistry has yielded the new complexes [Cu 2 (Hsucm) 3 (bpy) 2 ](NO 3 )·0.5MeOH ( 1 ·0.5MeOH), [Cu 2 (Hsucm)(OH)Cl(bpy) 2 ](OH)·3.6H 2 O ( 5 ·3.6H 2 O) and [Cu 2 (Hsucm) 2 Cl 2 (phen) 2 ] ( 6 ). The succinamate(−1) ion behaves as a carboxylate ligand and exists in two different coordination modes in the structures of the above complexes, i.e., the common syn , syn μ 2 -κ O :κ O ′ in 1 , 5 and 6 , and the μ 2 -κ 2 O :κ O ′ in 1 . The primary amide group of Hsucm − remains uncoordinated and participates in intermolecular hydrogen bonding interactions leading to 1D, 2D and 3D networks. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the Hsucm − ligands.

The synthetic investigation of the Cu(ClO4)2·6H2O/fumaric acid (H2fum)/N,N’-chelates (1,10-phen, 2,2′-bpy) tertiary reaction systems has yielded mononuclear, dinuclear and tetranuclear complexes, and three coordination polymers. The chemical and structural identity of the products depends on the solvent, the absence or presence of external hydroxides in the reaction mixtures and the N,N’-donor. Three fumarato(−2) complexes, i.e. compounds [Cu2(fum)(phen)4](ClO4)2·2H2O (1·2H2O), [Cu(fum)(phen)(H2O)]n (3) and [Cu2(fum)(bpy)2(H2O)2]n(ClO4)2n (6), were isolated and structurally characterized, and four non-fumarato complexes, i.e. compounds [Cu4(μ3-ΟΗ)2(μ2-ΟΗ)2(phen)4(H2O)2](ClO4)4·2H2O (2·2H2O), [Cu(ClO4)(phen) (MeCN)2(H2O)](ClO4) (4), [Cu(ClO4)(phen)(MeCN)2]n(ClO4)n (5) and [Cu(ClO4)2(bpy)(MeCN)2] (7), were simultaneously obtained from the reaction systems investigated. The coordination versatility of the fumarato(−2) ligand is reflected to the three different coordination modes observed in 1·2H2O, 3 and 6; the monodentate bridging μ2-κO:κO′ mode in 3, the asymmetric chelating bridging μ2-κO:κO′:κO′′:κO′′′ mode in 1·2H2O and 3, and the syn,syn bridging μ4-κO:κO′:κO′′:κO′′′ mode in 6. The crystal structures of the complexes are stabilized by intra- and inter-molecular hydrogen bonding and π–π stacking interactions leading to interesting supramolecular architectures. Characteristic IR bands of the complexes are discussed in terms of the known structures, and the coordination modes of the fum2− ligands.

The reactions of representative 2-pyridyl oximes with NiII salts in the presence of a base have been investigated. The synthetic study has led to the new triangular complexes [Νi3(ppko)6]·2H2O·0.5EtOH·MeOH (1·2H2O·0.5EtOH·MeOH), [Νi3(mpko)3(HCO2)2(mpkoH)2](ClO4) (2) and [Νi3(ppko)3(HCO2)2(ppkoH)2](ClO4) (3), where ppko− is the anion of phenyl(2-pyridyl)ketone oxime and mpko− is the anion of methyl(2-pyridyl)ketone oxime. The structures of compounds 1 and 2 have been determined by single crystal X-ray diffraction. The ppko− ligand in 1 adopts four different coordination modes including the unique NpyridylOoximate chelating one which gives rise to a 6-membered chelating ring, while the neutral and the deprotonated oxime ligands in 2 adopt three different coordination modes. The magnetic properties of 1 and 2 have been studied by variable-temperature dc magnetic susceptibility techniques which indicate antiferromagnetic interactions.

Employing the mononuclear complex [Ni{(py)C(Me)NO}2{(py)C(Me)NOH}] (1) as ‘ligand’ [(py)C(Me)NOH = methyl 2-pyridyl ketone oxime], the use of the ‘metal complexes as ligands’ approach has led to the synthesis of the mixed NiII/LnIII complexes [NiTb{(py)C(Me)NO}2(NO3)3{(py)C(Me)NOH}] (2), [Ni2Ln2{(py)C(Me)NO}6(NO3)4] (Ln = Dy, 3; Ln = Tb, 4) and [Ni2Tb{(py)C(Me)NO}6](NO3) (5). The structures of 2, 3, and 5, and the magnetic properties of 2 and 5 are briefly discussed.

The use of the 2-pyridyl oxime ligands (LH) 2-pyridinealdoxime, methyl 2-pyridyl ketone oxime and phenyl 2-pyridyl ketone oxime in Co chemistry has been investigated and led to two families of compounds. The first family includes the mononuclear octahedral, low-spin complexes [CoIII(L)3], while the second family consists of the trinuclear, mixed-valent linear clusters [ Co III 2 CoII(L)6]X2 (X = ClO 4 - , PF 6 - ). The latter are prepared by the reactions of the former with an appropriate CoII source. The structural, physical and spectroscopic properties of the complexes are described.

The reaction of 1-hydroxybenzotriazole, btaOH, with nickel(II) acetate tetrahydrate, in the absence of an external base, has been investigated. The reaction of Ni(O2CMe)2 · 4H2O with one equivalent of btaOH in nPrOH leads to the the first structurally characterized tridecanuclear nickel(II) cluster and the biggest metal/btaOH or btaO− cluster discovered to date, [Ni13(OH)6(O2CMe)8(btaO)12(H2O)6(nPrOH)4] · 6.6H2O · 4(nPrOH) (1 · 6.6H2O · 4(nPrOH)). The centrosymmetric molecule contains the {Ni13(μ3-ΟΗ)6(μ3-ONNNR)12}8+ core (R– = C6H4–) and is characterized by competitive antiferromagnetic exchange interactions within its pentanuclear subunits containing the μ3-ΟΗ− bridges. The reaction of 1 with an excess of N 3 - ions in refluxing MeOH has led to the azido-bridged product [Ni13(N3)6(O2CMe)8(btaO)12(MeOH)10] (2), in which the spin frustration observed in 1 seems to disappear.

The employment of di-2-pyridyl ketone, (py)2CO, in manganese(II) benzoate chemistry is reported. The syntheses, crystal structures and spectroscopic (IR, EPR) characterization are described for [ Mn 3 II (O2CPh)6{(py)2CO}2] (1), [ Mn 3 II (O2CPh)6{(py)2CO}2] · 2MeCN (2 · 2MeCN) and [ Mn 4 II (O2CPh)4{(py)2C(OH)O}4] (3), where (py)2C(OH)O− is the monoanion of the gem-diol form of (py)2CO. Variable-temperature, magnetic susceptibility studies on 3 have also been performed. Complexes 1 and 2 · 2MeCN are linkage isomers. The trinuclear molecules of both complexes have a linear structure, with one η1:η2:μ2 and two syn, syn- η1:η1:μ2 PhCO 2 - groups spanning each pair of MnII atoms. The terminal MnII atoms are each capped by one κ2N,N′ (py)2CO ligand in orange 1 and one κ2N,Ο (py)2CO molecule in the yellow isomer 2 · 2MeCN. The molecule of 3 has a cubane topology with the MnII centers and the deprotonated oxygen atoms from the η1:η3:η1:μ3 ligands occupying alternate vertices of the cube. A terminal monodentate PhCO 2 - group completes a distorted octahedral coordination at each MnII atom. The IR data are discussed in terms of the coordination modes of the ligands that are present in the complexes. The X-band EPR spectra of powdered 1 and 2 at 4 K indicate that the populated spin states exhibit a zero-field splitting, while the spectrum of 3 at 18 K is consistent with the presence of magnetically interacting MnII atoms in the solid state. The magnetic properties of 3 in the 300–5 K range have been modelled with two J values, which reveal weak antiferromagnetic interactions within the molecule. Some suggestions have been made concerning the great stability of complex 3.

The employment of the di-2-pyridyl ketone [ ( py ) 2 CO ] / PhCO 2 - / N 3 - ligand combination in copper(II) chemistry has provided access to the hexanuclear cluster [Cu6(O2CPh)4(N3)2{(py)2CO2}2{(py)2C(OH)O}2] (1), and the coordination polymers [Cu4(O2CPh)2(N3)4{(py)2C(OMe)O}2]n (2) and [Cu2(O2CPh)(N3)2{(py)2C(OMe)O}]n (3). The structural type (cluster versus polymer) depends on the reaction solvent. Complex 1 has a [CuII6(μ3-OR′′)2(μ-OR′′)4]6+ core based on a central defective cubane unit and two additional CuII atoms across the missing edges. Complex 2 consists of zig-zag chains and complex 3 consists of extended 2D networks that adopt the herringbone architecture which is not based on T-shaped nodes. Cluster 1 is antiferromagnetically coupled with an S = 0 ground state.

The novel heteroleptic complex (gu)2[Nb(O2)3(quin-2-c)] · H2O (1) has been prepared by substituting a peroxo group by quinoline-2-carboxylate ion in the homoleptic complex (gu)3[Nb(O2)4] (2) in the presence of an excess of hydrogen peroxide in aqueous medium (gu+ = CN 3 H 6 + ; quin-2-c = quinoline-2-carboxylate ion). The complexes contain the highly symmetric and planar guanidinium ion as a counter-ion, which exhibits high stability and an extended hydrogen bonding pattern. The crystal structure and the spectral characterization of (gu)2[Nb(O2)3(quin-2-c)] · H2O have been determined. The ground electronic structure of the complex has been calculated with the density functional theory (DFT) method, and TD-DFT calculations have been employed to interpret the UV–Vis transitions. Compilation of the experimental and theoretical results may permit us to produce additional information about binding and catalytic reactivity.

A general method of increasing the ground-state total spin value of a polynuclear 3d-metal complex is illustrated through selected examples from cobalt(II) and nickel(II) cluster chemistry that involves the dianion of the gem-diol form of di-2-pyridyl ketone and carboxylate ions as organic ligands. The approach is based on the replacement of hydroxo bridges, that most often propagate antiferromagnetic exchange interactions, by the end-on azido ligand, which is a ferromagnetic coupler.

The use of 2-pyridyl oximes (L’H) in reactions with [ Mn 3 III O ( O 2 CR ) 6 ( py ) 3 ] ( ClO 4 ) has led to complexes [ Mn 3 III O ( O 2 CR ) 3 L 3 ′ ] ( ClO 4 ) . Ferromagnetic exchange interactions between the three MnIII ions in the complexes lead to spin ground states of S = 6. The complexes display the temperature- and scan rate-dependent hysteresis loops that are indicative of single-molecule magnetism behaviour.

The iron complexes with the phenoxyalkanoic acids 3,4-D, 2,3-D and 2,4,5-T in the presence or not of a nitrogen donor heterocyclic ligand, phen, were prepared and characterized. Interaction of Fe(III) with phenoxyalkanoic acids and phen leads to dinuclear neutral complexes while the absence of phen favours trinuclear cationic or tetranuclear neutral forms. The crystal structure of hexakis(2,3-dichlorophenoxyacetato)tris(methanol)oxotri-iron(III) chloride–methanol(1/3), [Fe3O(2,3-D)6(MeOH)3]Cl · 3MeOH (2), and tetrakis(dimethyl-sulfoxide)octakis(2,4,5-trichlorophenoxyacetato)dioxotetra-iron(III) methanol(1/2)–water(1/1)–dimethylsulfoxide(1/0.8), {[Fe4O2(2,4,5-T)8(dmso)4] · 2MeOH · H2O · 0.8dmso} (3), have been determined and refined by least-squares methods using three-dimensional Mo Kα data. Magnetic data of the trimer show antiferromagnetic interaction. The ground state of the system is S = 1/2 with a small percentage of S = 5/2 paramagnetic impurity ρ = 0.7%. For the tetramer, the magnetic data suggest antiferromagnetically coupled system with S = 0 ground state, while for the dimer, {[Fe2OCl2(3,4-D)2(phen)2] · H2O · 3.5MeOH} a very strong antiferromagnetic exchange interaction between the two ions has been observed. The fitting results give an exchange interaction of J = 254.1 cm−1, with S = 0 ground state with a small amount of paramagnetic S = 5/2 impurity (ρ = 0.3%).

The use of 4-(hydroxymethyl)pyridine (4hmpH) and pyrimidine (pym) in manganese benzoate chemistry has been investigated. The reactions of 4hmpH and pym with Mn(O2CPh)2 · 2H2O in MeCN affords the complexes [Mn6O2(O2CPh)10(4hmpH)3 (MeCN)] (1) and [Mn6O2(O2CPh)10(pym)2(MeCN)2] (2), respectively. Complex 1 contains a {Mn6O2}10+ core that can be conveniently described as two edge-sharing Mn4 tetrahedra at the center of each of which is a μ4-O2− ion. Peripheral ligation to the octahedrally coordinated Mn centres is provided by 10 bridging PhCO 2 - ligands, three N-monodentate ligands and one terminal MeCN group. The complex is mixed-valence ( Mn 4 II Mn 2 III ) and the MnIII ions are assigned as the two central metal centres bridged by two O2− ions. The molecular structure of 2 is very similar to that of 1, except that the terminal ligands are two monodentate pym molecules and two MeCN groups. IR data are discussed in terms of the nature of bonding and the known structures. Complexes 1 and 2 were characterized by variable-temperature ac and dc magnetic susceptibility data and found to possess a total spin ground state of 0. The ST = 0 ground state is explained in terms of the strong antiferromagnetic coupling within the central Mn 2 III O 2 unit.

Complexes [Fe2O(O2CCCl3)2(phen)2(H2O)2](ClO4)2 (1) and [Fe2O(O2CCMe3)2(phen)2(H2O)2](ClO4)2 (2) were obtained from the Fe(ClO4)3 · 9H2O/NaO2CR/phen reaction system (1: R = CCl3, 2: R = CMe3) in the 1:1.75:1 molar ratio in MeCN. 1 · MeCN · 1.5H2O crystallizes in the Monoclinic C2/c space group, whereas 2 · MeCN crystallizes in the triclinic P 1 ¯ space group. Both contain the {Fe2(μ-O)(O2CR)2}2+ metal core and exhibit similar structures. Their Mossbauer spectra consist of highly symmetric and very narrow quadrupole-split doublets with parameters (δ = 0.52 mm s−1 and ΔEQ = 1.81 mm s−1 (1) and 1.60 mm s−1 (2) at 78 K) characteristic for oxo-bridged diferric clusters. Variable-temperature magnetic susceptibility measurements show a strong antiferromagnetic coupling with J = −153 cm−1 (H = −2JS1S2) for 1, which is the largest reported value for a μ-oxo-biscarboxylato bridged diferric cluster.

In order to study the reaction of molybdenum(VI) with dihydroxybenzoic acids (DHBAs), compounds (PPh4)2 · [Mo4O6(μ-O)4(μ3-OCH3)2(2,3-DHBA)2] (1) and (PPh4)2 · [Mo3O6(μ-O)2(2,5-DHBA)2] · CH3CN (2) were isolated and determined by X-ray crystallography. The structure of complex 1 consists of four distorted MoO6 octahedra with two cis- MoO 2 2 + units and two molybdenum atoms having each ligand coordinated and one terminal oxygen atom, while two triple bridged methanol molecules are present. The ligand 2,3-dihydroxybenzoic acid (2,3-DHBA) prefers the catecholate-type coordination with strong hydrogen bonding between the carboxylic hydrogen and the ortho-phenolic oxygen. The structure of complex 2 consists of three distorted MoO6 octahedra. The 2,5-dihydroxybenzoic acid (2,5-DHBA) acts as a tridentate ligand using both carboxyl oxygen atoms, giving thus an unusual trinuclear molybdenum complex with a unique coordination mode of the ligand. The compounds were further investigated using IR, UV–Vis, ESR and NMR spectroscopy, elemental and thermogravimetric analysis, as well as cyclic voltammetry.

The use of di-2-pyridyl ketone ((py) 2 CO)/SCN − “blend” in erbium(III) chemistry has yielded mononuclear and dinuclear complexes. The Er III /SCN − /(py) 2 CO reaction mixture in alcohols (MeOH, EtOH) gives complexes [Er(NCS) 3 {(py) 2 C(OR)(OH)} 3 ] (R = Me ( 1 ), Et ( 2 )), where (py) 2 C(OR)(OH) is the neutral hemiacetal derivative of (py) 2 CO. Incorporation of hydroxides in the methanolic reaction system leads to the isolation of [Er 2 (NCS) 3 {(py) 2 C(OMe)O} 3 (MeOH)] ( 3 ). Complex 3 can also be isolated by the reaction of 1 with three equivalents of NMe 4 OH in MeOH. The crystal structures of 2 · 0.3EtOH · 0.4H 2 O and 3 · MeOH have been solved by single-crystal X-ray crystallography. The Er III atom in the former is in a nine-coordinate, tricapped trigonal prismatic ligand environment. The (py) 2 C(OEt)(OH) molecules adopt the novel N(2-pyridyl), O(hydroxyl)-bidentate chelating mode, while three isothiocyanate ligands complete the coordination sphere of Er III . In complex 3 · MeOH the two Er III atoms are triply bridged by the deprotonated hydroxyl oxygen atoms of the η 1 :η 2 :η 1 :μ 2 (py) 2 C(OMe)O − ligands; three 2-pyridyl nitrogen atoms belonging to three different ligands and two isothiocyanate anions complete eight-coordination at one Er III atom, while eight-coordination at the other Er III atom is completed by three 2-pyridyl nitrogen atoms, one isothiocyanate ligand and one MeOH molecule. The coordination polyhedra of the eight donor atoms about both Er III atoms are best described as distorted dodecahedra. The complexes were studied by room-temperature effective magnetic moments and spectroscopic (IR, solid-state f–f) methods. All data are discussed in terms of the nature of bonding and known ( 2 , 3 ) or assigned ( 1 ) structures.

A ferric complex, [Fe3O(O2CPh)6(EtOH)2(N3)] · 2.4EtOH (1 · 2.4EtOH) has been synthesized through the reaction of basic iron benzoate with NaN3. It crystallizes in the C2/c space group and it contains a planar {Fe3(μ3-O)}7+ core typical of basic iron carboxylates. Mossbauer spectra above 80 K display asymmetric quadrupole-split doublets that are consistent with the existence of two iron sites with O6 and O5N environments in a 2:1 ratio, respectively. Below 80 K the linewidth increases and the asymmetry vanishes. Variable-temperature magnetic susceptibility studies reveal the interplay of antiferromagnetic interactions, which require a 2J model for their interpretation (two equal J and one different J′ exchange constants). The fitting process yields two minima (J = −26.4 cm−1, J′ = −40.0 cm−1 and J = −33.0 cm−1, J′ = −24.0 cm−1 for a H = −2ΣJijSiSj spin Hamiltonian formalism), both of which lead to S = 1/2 ground states. Solid-state EPR measurements corroborate the existence of an S = 1/2 ground state, also indicating weak intermolecular interactions leading to broadened signals.

The synthesis and spectroscopic characterization of new substituted porphyrinate complexes are reported. The investigated compounds are represented by the formula (Porph)M(Cl) where Porph are TpFPP, TPyP, β-Cl4TPP, β-Cl8TPP or β-Cl4TPP, and M=In or Tl. UV–Vis and NMR spectroscopies of the title complexes confirm the proposed molecular formula and are described extracting all plausible information. The study is completed by three X-ray structures of (β-Cl4TPP)Tl(Cl), (β-Cl4TPP)In(Cl) and (TpFTPP)Tl(Cl). Compounds (β-Cl4TPP)Tl(Cl) and (β-Cl4TPP)In(Cl) are isostructural and they were treated in a similar way. The chloride substituents on the porphyrin core were found to be disordered in both compounds and they were refined anisotropically with occupation factors free to vary. The porphyrin core is saddle distorted while there is no twist distortion as judged by the large values of the dihedral angles formed between the phenyl rings and the C20N4 mean plane. In compound (TpFTPP)In(Cl), the dihedral angles between the pentafluorophenyl rings and C20N4 are very close to the ideal value of 90°.

The full investigation of the synthetic possibilities in the Fe(ClO4)3 · 6H2O/NaO2 CMe/bpym reaction system, where bpym is 2,2′-bipyrimidine, in MeCN has provided access to only one product. This is the dinuclear complex [Fe2O(O2CMe)2(bpym)2(H2O)2](ClO4)2 · H2O · 2MeCN (3 · H2O · 2MeCN). Its cation contains the (μ-oxo)bis(μ-carboxylato)diiron(III) core, while a chelating bpym molecule and one aquo ligand complete a distorted octahedral coordination at each metal ion. The complex cations participate in intercationic hydrogen bonds creating chains along the b axis, which form pairs due to π–π interactions between bpym rings of adjacent chains. The complex has been characterized by IR spectroscopy; characteristic bands are discussed in terms of the known structure and the coordination modes of the ligands. The room-temperature effective magnetic moment of 3 is 1.81 BM, a value indicating the presence of relatively strong antiferromagnetic interaction. The FeIII/ClO4 −/MeCO2 −/bpym chemistry is compared to the already well-developed FeIII/ClO4 −/MeCO2 −/bpy (bpy=2,2′-bipyridine) chemistry.

The preparation and crystal structures of four MnII carboxylate complexes containing 2-pyridinealdoxime, (py)CHNOH, are reported. The 1:1 reaction between Mn(O2CPh)2 · 2H2O and (py)CHNOH in MeCN, followed by evaporation of the resulting solution, redissolution of the residue in CHCl3 and precipitation with Et2O leads to isolation of [Mn4(O2CPh)6{(py)CO2}2{(py)CHNOH}2] · 0.6CHCl3 (1 · 0.6CHCl3). The most interesting synthetic feature is the in situ formation of the picolinate(−1) ligand, (py)CO2 −. The centrosymmetric tetranuclear cluster consists of an exactly planar zig-zag array of MnII ions and is held together by four syn, syn η1:η2:μ2 and two η1:η2:μ3 PhCO2 − groups, two η1:η2:μ2 (py)CO2 − ligands and two N,N′-bidentate chelating (py)CHNOH molecules. The 1:4:7 [Mn3 II,III, IIIO(O2CPh)6(pyr)2(H2O)]/Me3SiCl/(py)CHNOH reaction mixture in MeCN (pyr=pyridine) yields the 1D coordination polymer [Mn(O2CPh){(py)CO2}{(py)CHNOH}]n (2), in which the partial (py)CHNOH → (py)CO2 − transformation has again occurred. In each chain the MnII ions are bridged by syn, anti carboxylate groups of the η1:η1:η1:μ2 (py)CO2 − ligands, while the monodentate PhCO2 − group and the N,N′-bidentate chelating (py)CHNOH molecule complete the octahedral coordination at each metal ion. The 1:3 reaction between Mn(O2CMe)2 · 4H2O and (py)CHNOH in EtOH leads to the isolation of the dinuclear complex [Mn2(O2CMe)2{(py)CO2}2{(py)CHNOH}2] (3); crystallography reveals again the partial (py)CHNOH → (py)CO2 − transformation. The dinuclear molecule is located at a centre of symmetry; the MnII ions are bridged by two oxygen atoms from the two symmetry-related η1:η1:μ2 (py)CO2 − ligands, whose nitrogen atoms are ligated to different metal ions. Each MnII ion is further coordinated by a monodentate MeCO2 − group and a N,N′-bidentate chelating (py)CHNOH molecule. Reaction of Mn(hfac)2 · 3H2O (hfacH=hexafluoroacetylacetone) with 1 equivalent of (py)CHNOH in CH2Cl2 yields complex [Mn(O2CCF3)2{(py)CHNOH}2] (4); the CF3CO2 − ligand is one of the decomposition products of the hfac− ligand. The MnII ion in 4 is coordinated by two monodentate CF3CO2 − groups and two N,N′-bidentate chelating (py)CHNOH ligands in a cis–cis–trans fashion. The four complexes have been characterised by IR spectroscopy; characteristic bands are discussed in terms of the known structures and the coordination modes of the ligands. Variable-temperature magnetic susceptibility and EPR studies indicate weak antiferromagnetic exchange interactions in 1.

In order to examine the possibilities of using lanthanide(III) ions in the crystal engineering of hydrogen bonded coordination complexes, the compounds [Ln(DMU)6][LnCl6] and [Ln(NO3)3(DMU)3] (Ln=Pr, Nd, Gd, Er; DMU=N,N′-dimethylurea) have been prepared from the reactions of DMU with the appropriate lanthanide(III) salts in alcohols. The representative complexes [Nd(DMU)6][NdCl6] (2) and [Nd(NO3)3(DMU)3] (6) have been structurally characterised by single-crystal X-ray studies. The structure of 2 consists of distorted octahedral [Nd(DMU)6]3+ and [NdCl6]3− ions. In the molecules of 6, the Nd(III) ion is in a nine-coordinate, monocapped square antiprismatic geometry, surrounded by three O-bonded DMU ligands and three bidentate chelating nitrate groups. The [Nd(DMU)6]3+ cations and [NdCl6]3− anions self-assemble to form a hydrogen-bonded 3D architecture in 2. The hydrogen bonding functionalities on the molecules of 6 create also a 3D structure. Two main motifs of interionic/intermolecular hydrogen bonds have been observed: NH⋯Cl in 2 and NH⋯O(NO3 −) in 6; weak CH⋯Cl hydrogen bonding interactions are also present in 2. The complexes were characterised by magnetic susceptibilities at room temperature and spectroscopic (IR, far-IR, Raman) techniques. The vibrational data are discussed in terms of the nature of bonding and the known structures of the neodymium(III) complexes.

The use of the substituted benzotriazole ligand btaOH (1-hydroxybenzotriazole) in nickel(II) chemistry has yielded a structurally and magnetically interesting polynuclear complex. The [Ni(acac)2(H2O)2]–btaOH·H2O (4:1, 3:1, 7:4) reaction system in refluxing MeCN gives light green–blue [Ni7(OH)2(acac)8(btaO)4(H2O)2] (4) in good yield (∼75%). The structure of 4·MeCN·0.9H2O was determined by single-crystal X-ray crystallography. The heptanuclear assembly is held together by two μ3 hydroxo ligands, two terminal H2O molecules, four chelating acac− groups, two μ2 acac− groups, two μ3 acac− groups, two μ4 btaO− ligands and two μ2 btaO− ligands. The Ni(II) atoms have distorted octahedral geometries. The IR and UV–Vis data of 4 are discussed in terms of the nature of bonding and the known structure. Variable-temperature magnetic susceptibility data (3–300 K), fitted with a 3-J model, show ferromagnetic and antiferromagnetic interactions. Magnetization data at 4 K are in line with an S=1 ground state for 4. The versatility of the 1-hydroxybenzotriazolate ligand is also discussed.

A systematic investigation of the reactions between metal ions and dipeptides containing the α-aminoisobutyric residue (Aib) was initiated. The solid complexes [Cu(H−1L)]n (1, 2) and (LH2)n[CuCl3]n (3) were isolated and characterized by single-crystal X-ray crystallography, solid-state IR spectra and UV–Vis spectroscopy in solution (H−1L2− is the dianionic form of H–Aib–Aib–OH). Of remarkable interest is the isolation of two complexes which have the same chemical formula, [Cu(H−1L)]n, but different structures. Complex 1 is a chain (1D) compound, while complex 2 is a 3D coordination polymer. The doubly deprotonated dipeptide behaves as a N(amino), N(peptide), O(carboxylate), O′(carboxylate) η1:η1:η1:η1:μ2 ligand in 1. In 2 the H−1L2− ligand binds to one CuII atom at its amino and peptide nitrogens and at one carboxylate oxygen, and to a second metal at the other carboxylate oxygen, while a third CuII atom is attached to the peptide oxygen. The structure of 3 consists of zigzag (CuCl3)n n− chains and protonated dipeptides (H2L+) which remain uncoordinated. Two neighbouring CuII atoms are bridged by two chloro ligands, while a terminal chloro ligand completes five coordination at each metal center. The IR data are discussed in terms of the nature of bonding and known structures. The UV–Vis spectra show that the solid-state structures of 1 and 2 do not persist in H2O.

Selected ‘3+1’ mixed ligand oxorhenium and oxotechnetium complexes containing the SNS/S donor atom set have been modified by introduction of a bifunctional amine anchor on the p -position of the thiophenolato monodentate ligand. A representative series of complexes containing several tridentate ligands was prepared both at macromolar (Re complexes) and nanomolar ( 99m Tc complexes) amounts. Coupling of these complexes to activated carboxylate groups was performed according to the ‘preformed chelate approach’ using benzoyl chloride as a model molecule. Coupling yields were high both at nanomolar and millimolar metal concentration, as revealed by high-performance liquid chromatographic analysis of 99m Tc and Re species adopting parallel radiometric and photometric detection modes. All Re compounds have been characterized by classical analytical methods. In addition, the structures of representative parent ReO[CH 3 SCH 2 CH 2 N(CH 2 CH 2 S) 2 ][ p -SC 6 H 4 NH 2 ] and daughter ReO[CH 3 SCH 2 CH 2 N(CH 2 CH 2 S) 2 ][ p -SC 6 H 4 NHCOC 6 H 5 ] complexes were solved by X-ray crystallography. Both compounds adopt a distorted trigonal bipyramidal geometry around rhenium, wherein the oxo group and the sulfur atoms of the SNS ligand occupy the equatorial plane and the nitrogen atom and the sulfur of the monothiol are located at the apical positions trans to each other.

A systematic investigation of the CuBr 2 /Mebta (Mebta=1-methylbenzotriazole) reaction system is described. Particular emphasis has been placed on determining the influence of the Mebta:Cu II ratio and the nature of solvent on the identity of the reaction products. These combined variations have led to the preparation of the following complexes; [CuBr 2 (Mebta)] n ( 1 ), [CuBr 2 (Mebta) 2 (MeCN)]·MeCN ( 2 ), [CuBr 2 (Mebta) 2 ] ( 3 ) and [CuBr 2 (Mebta) 3 ]·0.25H 2 O ( 4 ). Complexes 2 , 3 and 4 have been structurally characterized by single crystal X-ray studies. Mebta behaves as a monodentate ligand binding through N(3). The geometry about copper(II) in 3 is tetrahedrally distorted trans square planar, while complexes 2 and 4 have distorted trigonal bipyramidal stereochemistries. The new complexes were characterized by elemental analyses, magnetic susceptibilities at room temperature and spectroscopic (IR, far-IR, UV/VIS) techniques. A doubly bromo-bridged chain structure with two alternating chromophores is assigned for 1 . All data are discussed in terms of the nature of bonding and known or assigned structures. A comparison of the CuBr 2 /Mebta and CuCl 2 /Mebta systems is also presented.

The preparation and the characterization of nickel(II) complexes with the neutral, N4 non-macrocyclic Schiff base ligands L1=1,2-bis(2′-pyridylbenzyleneimino)benzene and L2=1,2-bis(2′-pyridylethyleneimino)benzene, of formulae Ni(LX)Cl2 are reported. The structure of the complex, [Ni(L1)Cl2] · EtOH, has been determined by X-ray diffraction methods. The nickel atom has a six coordinate NiN4Cl2chromophore with distorted octahedral coordination, while the ligand L acts as a tetradentatechelate, with the ligated atoms in an essentially planar arrangement around the metal and the remaining axial coordination sites occupied by chloro ligands. The reactions of the above complexes and that of Ni(L3)Cl2 with 1,4-phenyldiisocyanide (phdi) formed polymeric compounds of the type [(LX)Ni(phdi)]nCl2n which have been characterized by elemental analysis, magnetic susceptibility measurements, IR and UV-Visspectroscopic techniques. The solid state electrical conductivity of the polymeric complexes was approximately 10−7 (Ω · m)−1, which further increased by partial oxidation with I2.

The complex trans-[Ni(ONO2)2(LH2)2], where LH2 is the new ligand N,N′-bis(2-pyridyl)urea derived unexpectedly from nicotinic or isonicotinic acid and 2-aminopyridine, was isolated. The ligand and its complex have been characterized by a variety of physical and spectroscopic techniques. The crystal structure of the complex reveals that LH2 behaves as a bidentate chelate with ligated atoms being the amide oxygen and one of the pyridyl nitrogens.

The complexes trans-[M(LH)2(H2O)2] (M = Mn, Co, Ni, Cu, Zn; LH− = the monoanion of malonamic acid) have been synthesized and the X-ray crystal structures of the copper (II) and zinc (II) complexes show an octahedral geometry around the metal ion in both molecules. The ligand LH− acts as a bidentate chelate with ligated atoms being the amide and one of the carboxylate oxygens. Both structures are stabilized through similar, intermolecular 2D hydrogen bonds. The thermal decomposition data, magnetic susceptibilities, and electronic, variable-temperature ESR and FT-IR spectra of the complexes are discussed in terms of the nature of bonding and known structures.

A systematic investigation of the NiX2/Mebta (X = Cl, Br, NCS, NO3; Mebta = 1-methylbenzotriazole) reaction system in various solvents is described. Particular emphasis has been placed on determining the influence of the Mebta: Ni11 ratio on the identity of the reaction products. In the nitrate case, the influence of the water concentration in the reaction mixture on reaction products has also been investigated. These combined variations have led to the preparation of 14 discrete six-coordinate complexes with the formulae [Ni(NO)3)2(Mebta)2], [Ni(NO3)(H2O)2(Mebta)2]NO3, [Ni(H2O)4 (Mebta)2](NO3)2, [Ni(NO3)2(Mebta)3]·CH3COCH3, [NiX2(Mebta)4](X = ONO2, NCS, Cl, Br), [NiX2(Mebta)2]n (X = Cl, Br), [NiX2(MeOH)2(Mebta)2] (C = Br, NCS) and [NiX2 (Mebta)]n (X = Cl, Br). Four complexes have been structurally characterized by single-crystal X-ray studies: cis-[Ni(NO3)2(Mebta)2] (1), trans-[Ni(H2O)4)Mebta)2](NO3)2 (3), mer-[Ni(NO)3)2((Mebta)3]·CH3COCH3 )4) and trans-[Ni(NCS)2(MeOH)2(Mebta)2] (6). Mebta behaves as a monodentate ligand binding through N(3). The structures of 3and 6 are stabilized by intermolecular hydrogen bonds. The new complexes were studied by thermal techniques, conductivity measurements, magnetic susceptibilities and spectroscopic (IR, ligand field) methods. Monomeric, trans pseudo-octahedral structures are assigned for the complexes [NiX2(Mebta)4] and [NiBr2(MeOH)2(Mebta)2] in the solid state. Polymeric structures are suggested for [NiX2(Mebta)2]n and [NIX2(Mebta)]n with NiX4N2 and NiX5N coordination spheres, respectively.

An inorganic model approach to the corrosion inhibition of metals by benzotriazoles has been initiated. The preparation and characterization of monomeric cobalt(II) complexes of the types [CoX2(Mebta)2](X = Cl, Br, NCS, NO 3), (MebtaH)[CoCl3(Mebta)], (MebtaH)2[CoCl4], [Co(NCS)2(Mebta)4], [Co(NCS)2 (MeOH)2(Mebta)2] and [Co(NO3)2 L2(Mebta)2] (L = H2O, MeOH), where Mebta = 1-methylbenzotriazole, are described. Four representative complexes have been structurally characterized by single-crystal X-ray diffraction studies; [CoCl2(Mebta)2] (1), trans- [Co(NCS)2(Mebta)4] (5), trans-[Co(NCS)2 (MeOH)2(Mebta)2] (6) and cis-[Co(NO3)2(Mebta)2] (8). Mebta acts as a monodentateligand binding through N(3). The geometry about cobalt in 1 is tetrahedral, while complexes 5, 6 and 8 have octahedral stereochemistries. The new complexes were also characterized by elemental and thermogravimetric analyses, conductivity measurements, variable-temperature magnetochemistry and spectroscopic (IR, ligand field, low-temperature ESR) methods. The data are discussed in terms of the nature of bonding and known structures.

Reaction of the [N,N-diethyl,N′-ethylene (salicylideniminato)] (salicylato) copper(II) complex [Cu(SalNEt 2 )(Sal)] with squaric acid in CH 3 OH affords [Cu 2 (SalNEt 2 ) 2 (H 2 O)(C 4 O 4 )] · H 2 O, whose X-ray structure shows the first example of a binuclear copper(II) complex with an unusual μ-1,2-coordination mode for the bridging squarato (C 4 O 4 2− ) ligand. This type of linking leads to the shortest bimetallic distance, as well as to the largest antiferromagnetic interaction observed so far for squarato bridged copper(II) complexes.

The initial use of the picolinate (pic(-))/sulfate "blend" in metal chemistry has yielded two neutral coordination polymers. Complexes [Zn-2(SO4)(pic)(2)(H2O)(3)](n) (1) and [Cd-2(SO4)(pic)(2)(H2O)(3)](n) center dot nH(2)O (2 center dot nH(2)O) were prepared by the reaction of MSO4 center dot xH(2)O [M = Zn, x = 7; M = Cd, x = 8/3] with one equivalent of picolinic acid (picH) in aqueous solution in the absence of external base. The structures of both compounds have been determined by single-crystal X-ray crystallography. Complex I consists of helical chains which interact through hydrogen bonds and stacking interactions to form a 3D, 5-connected network. Complex 2 - nH(2)O consists of ribbons that are crosslinked by the sulfato ligands to give a 2D, 4-connected network. Hydrogen bonds and stacking interactions lead to the formation of a 3D supramolecular architecture. In both coordination complexes, the pic ligand adopts two different bridging coordination modes (2.111 and 2.201 in 1; 2.211 and 2.201 in 2 center dot nH(2)O), while the SO42- behaves as a bidentate bridging 2.1100 (Harris notation) ligand. The Zn(II) complex has 5- and 6-coordinate metal ions, whereas 6- and 7-coordinate Cd-11 atoms are present in 2 - nH(2)O. Characteristic vibrational (IR, Raman) bands are discussed in terms of the known structures, and the coordination modes of the pic(-) and SO42- ligands. The thermal decomposition of the Cd(11) compound has also been studied. (C) 2007 Elsevier Ltd. All rights reserved.