Search

Reactions between 3-amine-2-((pyridin-2-ylmethyl)selanyl)pyridine (L) and MX2 (M = Co, Cu, Zn; X = Cl, Br) result in the formation of the metal(II) molecular complexes 1–5 with the general formula [MX2(L)]. The organic ligand is coordinated to the metal center through nitrogen atoms of the pyridine rings, without interaction with the selenium atom. The rhenium(V) complex [ReO(apySe)2]Cl (6) is formed in two different ways, using [ReOCl3(PPh3)2] as precursor. Firstly, the formation of 6 was observed in the mother liquor, through Csp3–Se bond cleavage of the ligand L and formation of new Re–Se bonds. Secondly, the direct reaction between bis(3-amino-2-pyridyl)diselane (apySe)2 and [ReOCl3(PPh3)2] gave complex 6 in higher yields. The coordination compounds were characterized by spectroscopic and crystallographic methods. Furthermore, the antibacterial activity of the complexes 1–5 was evaluated against Gram-positive bacteria, Staphylococcus aureus (ATCC® 25923), and Gram-negative bacteria, Escherichia coli (ATCC® 25922). The results suggest that the complexes [CoCl2(L)] (1), [CuCl2(L)] (3), [CuBr2(L)] (4) and, [ZnCl2(L)] (5) possess significant bactericidal activity when compared with those of the free ligand and metal salts used in the synthesis.

Five new PdII complexes are reported and have been obtained by the reaction of monomeric [Pd(bipy)(py)2]2+, which serves as a builing block, and substituted (ArSe)2 or Pd(SeAr)2. Complexes [Pd2(μ-SeAr)2(bipy)2](PF6)2, Ar = Ph (1), p-ClC6H4 (2), p-FC6H4 (3), [Pd3(μ3-Se)2(bipy)3](PF6)2·5THF (4) and [Pd3(μ-SeMes)4(bipy)2](PF6)2·2MeCN (5) showed that the nuclearity of these structures is affected by electron donating groups (EDGs) and electron withdrawing groups (EWGs) from the selenium-containing ligands, where changing the stoichiometry ratio of the reactants does not affect the number of palladium centers. The distinct behaviors of 1–5 in the solid state, solution phase and gas phase were investigated by single-crystal XRD, NMR and ESI-TOF-MS. In solution, the dinuclear 1–3 structures exist in equilibrium with trinuclear species. In the gas phase, trinuclear and tetranuclear aggregates of 1–3 are detected, as well as dinuclear and tetranuclear aggregates for 5, while compound 4 maintains the same nuclearity. The solid-state electrochemical behavior was studied, and all complexes were electrochemically active, exhibiting irreversible electrochemical processes, where selenium is indicated to be the active species which oxidizes under such conditions. The complexes are potential candidates to act as semiconductor sensitizers for photocatalytic hydrogen evolution, as they absorb in the visible region with optical band gap energies in the range of 2.6 eV.

Reactions of 2,6-dipicolinoylbis(N,N-diethylthiourea), H2Lpy, InCl3, MCl salts (M = Rb+, K+, Na+ or NH4+) and NEt3 in methanol give cationic {2}-metallacryptates of the composition [M⊂{In2(Lpy)3}]+ (M+ = Rb+, K+, Na+ or NH4+). They can be isolated as PF6− salts. The structural characterization of the products by means of spectroscopic methods and X-ray crystallography reveals host–guest assemblies, in which a monovalent guest cation M+ is encapsulated in the cryptand-like host compound {In2(Lpy)3}. The host–guest directional interactions are coordination or hydrogen bonds depending on the nature of the guest cation. A 15N NMR spectroscopic study on the inclusion compound with 15NH4+ cations reveals a dynamic structure of the corresponding {2}-metallacryptate in solution and partial exchange of the ammonium ions by coordinating solvents.

Nine thiosemicarbazone ligands (H2Ln, n = 1–9) containing benzothiazole or benzoxazole groups at the C(2) atom of the thiosemicarbazone have been prepared and characterized. A crystal structure study was performed on six of these free ligands and the role of the π–π interactions in the molecular association was analyzed. The coordination behavior of the thiosemicarbazones towards the {Re(CO)3}+ fragment was investigated and three types of complexes were obtained: mononuclear fac-[ReX(H2Ln)(CO)3], X = Cl or Br, with bidentate ligands, dinuclear [Re2(HLn)2(CO)6] with monodeprotonated bridging thiosemicarbazonates yielding Re2S2 cores and tetranuclear [Re4(L2)2(CO)12(EtOH)2] with an unusual bideprotonated thiosemicarbazonate ligand. The intermolecular interactions before and after metal coordination were analyzed. In the dinuclear complexes, two different approximate symmetries were observed depending on the relative orientation of the thiosemicarbazonate ligands with respect to the Re2S2 diamond. The intramolecular interactions in the dimers and their relationship with the two possible symmetric dispositions were analyzed. The findings, in conjunction with theoretical calculations, allowed the main stabilizing factors for each type of symmetry to be elucidated.

Reactions of (NBu4)[TcOCl4] or [TcCl3(PPh3)2(CH3CN)] with in situ-prepared lithium arylselenolates and -tellurolates give (NBu4)[TcVO(ArE)4] (E = Se, Te; Ar = phenyl) and [TcIII(ArE)3(PPh3)(CH3CN)] (E = Se, Te; Ar = phenyl, 2,6-Me2phenyl, mesityl) complexes, respectively. The products contain square-pyramidal (TcV compounds) and trigonal bipyramidal (TcIII complexes) coordinated technetium atoms. Density functional theory calculations indicate that the Tc–chalcogen bonds in the TcIII compounds have a greater bond order than those in the TcV compounds.

Fluoridotetrakis(trifluoroacetato)nitrosyltechnetate(II) was prepared by the dissolution of Cs2[Tc(NO)F5] in trifluoroacetic acid and addition of (NBu4)F·3H2O. The compound crystallizes as a mixed Cs+/NBu4+ salt in the form of green crystals. Unlike the [Tc(NO)F5]2− salts, the product is soluble in organic solvents and can be used as a precursor for ongoing ligand exchange procedures with organic ligands. The corresponding reactions with triphenylphosphine (PPh3), 1,2-bis(diphenylphosphino)ethane (DPPE) or pyridyldiphenylphosphine (pyPPh2) give technetium(I) complexes of the compositions Cs[Tc(NO)(PPh3)2(CF3COO)2F], [Tc(NO)(DPPE)2(OOCCF3)](PF6) and [Tc(NO)(κN,P-pyPPh2)(κP-pyPPh2)(CF3COO)2]. The products were studied spectroscopically and by X-ray diffraction. The 99Tc NMR resonances of the novel Tc(I) nitrosyls appear between −627 and +952 ppm, which is at a remarkably high field and in the range where normally the signals of Tc(III) compounds are observed.

Reactions between [Tc(I)(NO)X2(PPh3)2(CH3CN)] complexes (X = Cl, Br) and KCp form the pseudotetrahedral organotechnetium compounds [Tc(I)(NO)(Cp)(PPh3)X]. The halide ligands can readily be replaced by other halides or organometallic ligands giving access to a novel family of technetium(i) compounds with the robust {Tc(NO)(Cp)(PPh3)}(+) core.

Bis(2-pyridyl)diselenoethers with the general formula (2-PySe)2(CH2)n [n = 1, 3 and 4] react with CuI, AgNO3, CuCl2·2H2O and CoCl2·6H2O resulting in the formation of products with molecular or multidimensional structures depending on the stoichiometry of the reactants and the conditions applied. The versatility of this class of selenium-containing ligands is demonstrated with the synthesis and structural characterization of six new complexes of the composition [CuCl2{(2-PySe)2CH2}]n (1), [Cu4I4{(2-PySe)2CH2}2] (2), [CuCl2{(2-PySe)2(CH2)3}2] (3), [CoCl2{(2-PySe)2(CH2)3}]n (4), [Ag{(2-PySe)2–(CH2)}3]n(NO3)n (5) and [CuCl2{(2-PySe)2(CH2)4}]n (6), respectively. The Cu(I) complex (2) was tested as catalyst in cross-coupling reactions.

Dimeric complexes of composition [Re2X2(CO)6(HL)2] were obtained by reaction of fac-[ReX(CO)3(CH3CN)2] (X = Cl, Br) with 4-acetylpyridine thiosemicarbazone (HLH) and derivatives in which the thioamide nitrogen bore Me or Ph (HLMe and HLPh, respectively). In these complexes, which were characterized by X-ray crystallography and FAB, IR and 1H NMR spectroscopies, the thiosemicarbazone ligands bridge between two rhenium atoms by coordination of their Npyridine and S atoms. This coordination mode is unusual in that it does not involve any of the thiosemicarbazide nitrogen atoms. The isolation of dimeric complexes rather than monomers or polymers seems to have been due to their poor solubility and rapid precipitation from the reaction medium. [Re2Cl2(CO)6(HLH)2] (1a) was isolated in unsolvated form and as its acetone and acetonitrile solvates; [Re2Br2(CO)6(HLH)2] as its methanol solvate; and all the other complexes as acetone solvates. In all the solvated crystals except those of [Re2Cl2(CO)6(HLPh)2] (3a), all the solvent molecules are hydrogen-bonded to the complex, and in those of [Re2X2(CO)6(HLH)2] these hydrogen bonds contribute significantly to the cohesion of the structure (in particular, in [Re2Br2(CO)6(HLH)2]·2CH3OH there are no hydrogen bonds directly linking the dimers). In 3a·2(CH3)2CO the dimers are linked by N–H⋯π and C–H⋯O interactions, and the non-hydrogen-bonded solvent molecules occupy channels with interatomic long and short diameters of 8.5 and 5.6 A, respectively.

Novel thiosemicarbazonato complexes of gold(III) have been prepared from reactions of [Au(damp-C1,N)Cl2 (damp- = 2-(N,N-dimethylaminomethyl)phenyl) or [NBu4][AuCl4] with 2-pyridineformamide thiosemicarbazones (HL). The thiosemicarbazones deprotonate and coordinate as mononegative, tridentate NNS ligands to gold to give [Au(Hdamp-C1)(L)]Cl2 or [AuCl(L)]Cl complexes. The organometallic damp− ligand is protonated during the reactions and the Au–N bond is cleaved. The [AuCl(L)]+ cations represent the first gold(III) complexes with thiourea derivatives which are not stabilised by an additional organometallic ligand. Reactions of [NBu4][AuX4] (X = Cl, Br) with diphenylthiocarbazone (dithizone) result in reduction of the metal and the formation of gold(I) complexes of the composition [AuX(SCN4-3,4-Ph2)] where SCN4-3,4-Ph2 is 3,4-diphenyltetrazole thione which is formed from cyclisation of dithizone.

Graphical contents entry Thiosemicarbazones react with [Au(damp-C1,N)Cl2] under cleavage of the Au-N bond and protonation of the dimethylamino group to give cationic or neutral Au(III) complexes. The products have remarkable biological properties. Summary: Dichloro[2-(N,N-dimethylaminomethyl)phenyl-C1,N]gold(III), [Au(damp-C1,N)Cl2], reacts with salicylaldehyde thiosemicarbazone (H2saltsc), vanilline thiosemicarba-zone (Hvantsc), N-methylpyrrole aldehyde thiosemicarbazone (Hmepyrtsc), pyridoxal meth-ylthiosemicarbazone (H2pydoxmetsc), 2-diphenylphosphinobenzaldehyde thiosemicarbazone (HPtsc) or variously substituted acetylpyridine thiosemicarbazones (HapRtsc; R = H, me, ph) under cleavage of the Au-N bond and protonation of the dimethylamino group. Compounds of the general formulae [Au(Hdamp-C1)Cl(L)]+ (L = Hsaltsc-, vantsc-, mepyrtsc-), [Au(Hdamp-C1)Cl(L)]2+ (L = H2pydoxmetsc) or [Au(Hdamp-C1)(L)]2+ (L = Ptsc-, apRtsc-, R = H, me, ph) have been isolated and characterized. The presence of the s-bonded 2-(dimethylaminomethyl)phenyl ligand is mandatory to prevent reduction of the gold(III) cen-tre. The crystal structures of [Au(Hdamp-C1)Cl(Hsaltsc)]-(PF6), [Au(Hdamp-C1)Cl(H2pydox-metsc)]Cl2 · MeOH, [Au(Hdamp-C1)Cl(mepyrtsc)]Cl, [Au(Hdamp-C1)(apphtsc)]-Cl2 · 2 Me-OH and [Au(Hdamp-C1)(Ptsc)]Cl2 · MeOH · 0.5 Et2O have been elucidated showing the gold atoms in distorted square co-ordination environments. The potentially O,N,S tridentate ligands H2saltsc and H2pydoxmetsc co-ordinate bidentate and do not incorporate the OH groups in the chelating framework, whereas the HapRtsc's or Ptsc co-ordinate tridentate. Generally, one or more hydrogen atoms of the heterocyclic ligands and/or the NMe2H+ group form hydrogen bridges in the solid state structures. First results of antiproliferation tests on tumor cells prove considerable cytotoxicity of the new gold complexes.

The complexes cis-Pt(O2CNEt2)2(PR3)2 (R = Ph, Et) and Pt(O2CNEt2)2(DPPE) [DPPE = 1,2-bis(diphenylphosphino)ethane] were prepared by the reaction of the corresponding phosphino-chloro complexes of platinum with Ag(O2CNEt2). The new N,N-diethylcarbamato complexes are excellent precursors for the high-yielding preparation of the corresponding carbonato derivatives Pt(CO3)(PR3)2 or Pt(CO3)(DPPE) by reaction with a stoichiometric amount of water. The carbamato complex cis-Pt(O2CNEt2)2(PPh3)2 reacts with CO producing the carbamoyl derivative cis-Pt[C(O)NEt2]2(PPh3)2. The chloro-carbamoyl complex, prepared by reacting cis-PtCl2(PPh3)2 with NHEt2 and CO, and recrystallized from toluene as the solvated species trans-PtCl[C(O)NEt2](PPh3)2·2 C6H5Me has been structurally characterized.

Dichloro[2-(dimethylaminomethyl)phenyl-C1,N]gold(III), [Au(damp-C1,N)Cl2], reacts with 2-mercapto-1,3-thiazoline (HSthiaz), 2-mercaptopyridine (HSpy), sodium 1-methylmercaptotetrazolate (NaSmetetraz), 4-methyl-3-mercapto-1,2,4-triazole (HSmetriaz) or 6-mercaptopurine (HSpur) under cleavage of the Au–N bond and protonation of the dimethylamino group. Compounds of general formulae [Au(Hdamp-C1)Cl(HL)2]2+ (HL = HSthiaz or HSpy), [Au(Hdamp-C1)Cl(L)] (L = Spur–) or [Au(Hdamp-C1)(L)3] (L = Smetetraz–) have been isolated and characterized. The reaction with HSmetriaz leads to a rapid reduction of the metal and the formation of the gold(I) complex [Au(HSmetriaz)2]+. The crystal structures of [Au(Hdamp-C1)Cl(HSthiaz)2]Cl2·Me2CO, [Au(Hdamp-C1)Cl(HSpy)2]·H2O, [Au(Hdamp-C1)(Smetetraz)3] and [Au(Hdamp-C1)Cl(Spur)]Cl have been elucidated showing the gold atoms in distorted square-planar co-ordination environments. Generally, one or more hydrogen atoms of the heterocyclic ligands and/or the NMe2H+ group form hydrogen bonds in the solid-state structures. The reaction of Na[AuCl4] with Na(Smetetraz) and [NEt4]Br yields bright red crystals of [NEt4][Au(Smetetraz)4], the first structurally characterized gold(III) complex with four monodentate thiolate ligands. The structure of the complex shows well separated [Au(Smetetraz)4]– anions with Au–S distances of 2.354(4) A.

The compound [NBu4][ReNCl4] has been found to be easily accessible by the reaction of [NBu4][ReO4] with sodium azide and HCl gas in ethanol and represents an excellent precursor for the synthesis of further rhenium nitrido complexes. It has been studied by X-ray crystallography. Rhenium(VI) compounds of the general formula [ReNX4(5)]–,2– (X = Br or NCS) were obtained when [NBu4][ReNCl4] reacts with HBr or KSCN. The products as well as mixed-ligand intermediates which are formed during the ligand exchange have been studied by EPR spectroscopy. The EPR parameters of the individual mixed-ligand compounds are clearly correlated to the composition of the co-ordination sphere and can be used to characterize the mixed-ligand species unambiguously. This is shown by a nearly linear dependence of g0, g||, a0Re and A||Re on the spin–orbit coupling constants of the equatorial donors. Reactions of [NBu4][ReNCl4] with most organic ligands yielded rhenium(V) compounds. A number of phosphine complexes and chelates with sulfur-containing ligands have been prepared and spectroscopically characterized. A crystallographic study on [ReN(Hdetcb)2] (Hdetcb– = N 2-diethylthiocarbamoylbenzamidinate) shows cis co-ordination for the chelating S,N-donor ligands. Weak intermolecular hydrogen bridges have been found between the co-ordinated nitrogen atoms and the lone pair of the nitrido nitrogen. A comparison between the crystal structural data of [NBu4]2[ReN(mnt)2] (mnt2– = 1,2-dicyanoethene-1,2-dithiolate), prepared from [NBu4][ReNCl4] and Na2mnt, and [NBu4][ReO(mnt)2] shows longer Re–S bonds in the nitrido anion but markedly higher O–Re–S bond angles indicating higher steric requirements of the oxo ligand compared with ‘N3–’.

Technetium(V) and rhenium(V) nitrido complexes of the compositions [MNL 2 ] and [MN(Cl)(PPhMe 2 )L] have been synthesized by reaction of Na[N(SPPh 2 ) 2 ] and [MNCl 2 (PPh 3 ) 2 ] or [MNCl 2 (PPhMe 2 ) 3 ] complexes, respectively [M = Re or Tc; L = N(SPPh 2 ) 2 - ]. The amide anion acts in all isolated complexes as a chelating ligand co-ordinated via the sulfur atoms. The complexes [TcN{N(SPPh 2 ) 2 } 2 ], [ReN{N(SPPh 2 ) 2 } 2 ] and [TcN(Cl)(PPhMe 2 ) 2 {N(SPPh 2 ) 2 }] have been studied by X-ray crystallography. The bis-chelates are five-co-ordinate with the nitrogen atoms at the apexes of square pyramids. The Tc atom in [TcN(Cl)(PPhMe 2 ) 2 {N(SPPh 2 ) 2 }] has a distorted-octahedral co-ordination sphere with Cl bonded trans to the nitrido function. The complex [ReN{N(SPPh 2 ) 2 } 2 ] is the first five-co-cordinate nitride which reacts with BCl 3 to form a nitrido bridge between rhenium and boron; [Re(NBCl 3 ){N(SPPh 2 ) 2 } 2 ] is characterized by a covalent N–B bond of 1.539(5) A. The Re–N multiple bond distance is only slightly influenced by addition of the Lewis acid. The complex [ReN(Cl)(PPhMe 2 ) 2 {N(SPPh 2 ) 2 }] reacts with BCl 3 with substitution of N(SPPh 2 ) 2 - and formation of the well known [Re(NBCl 3 )Cl 2 (PPhMe 2 ) 3 ]. The corresponding technetium complexes do not form Tc–N–B bridges upon reactions with BCl 3 . The [MN(Cl)(PPhMe 2 ) 2 {N(SPPh 2 ) 2 }] (M = Tc or Re) complexes reacted with S 2 Cl 2 to give thionitrosyl compounds with the metals in lower oxidation states; [Re(NS)Cl 2 (PPhMe 2 ) 3 ] and [Re(NS)Cl 3 (PPhMe 2 ) 2 ] have been characterized spectroscopically, [Tc(NS)Cl 3 (PPhMe 2 ) 2 ] was studied by X-ray diffraction and EPR spectroscopy. The phosphine ligands are trans to each other.

The dianionic rhenium(I) complex [ReBr3(CO)3]2– has been synthesized and characterized. This complex is an important starting material for compounds containing the fac-Re(CO)3 moiety since the three bromide ligands are very weakly bound. Particularly in co-ordinating solvents, the bromides are substituted by solvent molecules thus generating the strong 12e– Lewis acid [Re(H2O)3(CO)3]+2. This formula was confirmed, particularly in water, by IR spectroscopic methods. Complex 2 is stable in aqueous solution even when exposed to air for weeks. It has been titrated by NaOH solutions. The change in pH was detected potentiometrically and found to occur very slowly, indicating a reaction other than protonation deprotonation. Depending on the rate of titration and the total concentration of OH–, the two rhenium(I) hydroxo complexes [NEt4][Re3(µ3-OH)(µ-OH)3(CO)9] and [NEt4][Re2(µ-OH)3(CO)6] were isolated in good yield and structurally characterized. The former crystallizes in the orthorhombic space group Pnma with a= 10.752(7), b= 13.783(8) and c= 18.254(12)A. The skeletal framework is that of a cube lacking the Re(CO)3 unit in one corner. The latter crystallizes in the orthorhombic space group P2mm with Z= 1, a= 6.551(2), b= 7.413(2) and c= 12.084(2)A. The two Re(CO)3 moieties are bridged by three OH– ligands which create a mirror plane. A second mirror plane is perpendicular to it along the Re-Re axis.

The large cavity homoleptic thioether cages [R,R′-S6tricosane] (1-hydroxymethyl-9-methyl-3,7,11,15,18,22-hexathiabicyclo[7.7.7]tricosane) (1) and [R,R’-S6hexacosane] (1-hydroxymethyl-10-methyl-3,8,12,17,20,25-hexathiabicyclo-[8.8.8]hexacosane) (2) have been synthesized and the structures of 1 and of the complex {[Ag(2)]TsO}∞ have been elucidated, the latter showing a polymeric string structure with Ag+ coordinated by three different cages.

The syntheses of four S6-cages with different cavity sizes are described. In regard of potential applications for radioimmunotherapy with 111Ag, their coordination behaviour towards Ag(I) was evaluated by studies of their reactivity in solution and of their crystal structures. All cages reacted differently with Ag(I). Whereas S6-cages based on 3,8,12,17,20,25-hexathiabicyclo[8.8.8]-hexacosane (14) and on 5,9,17,21,28,31-hexathiabicyclo[11.11.11]pentatriacontane (18) showed only external Ag(I) coordination, successive adaptation of the cage size, yielded ligand 24, based on 4,7,13,21,24,25-hexathiabicyclo[8.8.8]hexacosane, which gave a complex with internal-peripheral Ag(I) binding.

Two molecular intermediates of the hydrolysis of technetium tetrachloride, cis-[TcCl4(H2O)2] and [Cl3(H2O)2TcOTc(H2O)2Cl3], were isolated and structurally characterised, suggesting that the hydrolytic degradation of technetium(IV) compounds occurs stepwise with the polymeric 'TcO2...nH2O' as a less defined final product.

Reduction of no-carrier added [188ReO4]–(ng range) in thf–[NBu4]Cl with BH3·thf under an atmosphere of CO yields [188ReCl3(CO)3]2– and [188Re3(µ-H)3(CO)12]; under similar conditions as with [188ReO4]–, the first µ-hydrido-bridged 99Tc hydrido carbonyl complex is prepared and structurally characterised.

Almost linear nitrogen bridges between rhenium and gallium are formed during the reaction of rhenium(V) complexes containing terminal ‘N3–’ ligands with gallium trichloride.

Characterisation of [TcO(L)], a novel technetium complex currently undergoing Phase II clinical trial evaluation for cerebral perfusion, is reported.