Chlorotriphenyl(quinolinium-2-carboxylato)tin(IV) monohydrate

The crystal structure of chlorotriphenyl(quinolinium-2-carboxylato)tin(IV) monohydrate is reported. The crystals are monoclinic, space group C2/c with cell parameters a = 20.048(3) Å, b = 11.724(1) Å, c = 23.291(3) Å, ]gb = 113.42(1), Z = 8, refined to R_F = 0.034 on 3331 observed reflections. The tin(IV) atom is five-coordinate, being found to three phenyl groups, the chlorine atom and an oxygen from the quinaldic acid. The geometry around the tin atom is trigonal bipyramidal, with the three phenyl groups occupying the equatorial positions, and the chlorine and quinaldic acid oxygen, the apical ones. The acidic proton of quinaldic acid has shifted position in the complex, and is bound to the heterocyclic nitrogen atom.The acid is thus coordinated in the form of a zwitterion. These trigonal bipyramidal units are linked together as dimers by pairs of water molecules, each of which hydrogen-bonds to the non-coordinated carboxylate oxygen atoms of both quinaldic acid molecules, plus the heterocyclic nitrogen atom of one quinaldic acid molecule. For complex formation with the protonated acid, the heterocyclic nitrogen should be alpha to the carboxylic acid group.     

Synthesis and structural studies on silvertin complex salts with cis-1,2-bis(diphenylphosphino)ethylene

Three new silver—tin complex salts with cis-1,2-bis(diphenylphosphino)ethylene have been synthesized. IR,³¹P and ¹¹⁹Sn NMR and conductivity data are reported and discussed together with the X-ray crystal structure of one of them, [Ag(cdppet)₂][SnPh₃(NO)₃)₂]. The silver atom is distorted tetrahedrally surrounded by the four phosphorus atoms of the two cdppet ligands. The tin atom is in a slightly distorted trigonal bipyramidal geometry with the phenyl carbon atoms in the equatorial plane and two oxygen atoms from monodentate nitrate groups at the apices.     

Crystal structure of [chloro(diethyldithiocarbamato)butyl phenyl]tin(IV)

The crystal structure of the title compound, SnCl(C₆H₅)(C₄H₉)[S₂CN(C₂H₅)₂], was determined and refined to an R factor of 3.2% for 4876 reflections. The molecule contains five-coordinate tin in a distorted trigonal bipyramidal arrangement with the tin atom lying 0.20 Å below the equatorial plane formed by one of the sulphur atoms, S(1), and the donor carbons of the butyl and phenyl groups. The chlorine and the other sulphur atom, S(2), occupy axial sites, making a S(2)SnCl angle of 156.85(1)°. The SnS(2) bond is markedly elongated (2.764(1) Å) compared to the SnCl bond (2.449(1) Å) and the SnS(1) bond (2.454(1) Å). The structure resembles those of analogues such as (C₆H₅)₂Sn(glygly) in having both hydrocarbon ligands located in the equatorial plane. Crystal data: space group P$\text{1}$: a = 8.291(2) Å, b = 14.726(3) Å, c = 9.509(2) Å, α = 96.24(2)°, β = 107.02(3)°, γ = 116.70(2)°, Z = 2, R = 3.2% for 4876 independent reflections.     

Diorganotin(IV) N-acetyl-l-cysteinate complexes: Synthesis, solid state, solution phase, DFT and biological investigations

Diorganotin(IV) complexes of N-acetyl-l-cysteine (H₂NAC; (R)-2-acetamido-3-sulfanylpropanoic acid) have been synthesized and their solid and solution-phase structural configurations investigated by FTIR, Mössbauer, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. FTIR results suggested that in R₂Sn(IV)NAC (R = Me, Bu, Ph) complexes NAC²⁻ behaves as dianionic tridentate ligand coordinating the tin(IV) atom, through ester-type carboxylate, acetate carbonyl oxygen atom and the deprotonated thiolate group. From ¹¹⁹Sn Mössbauer spectroscopy it could be inferred that the tin atom is pentacoordinated, with equatorial R₂Sn(IV) trigonal bipyramidal configuration. In DMSO-d₆ solution, NMR spectroscopic data showed the coordination of one solvent molecule to tin atom, while the coordination mode of the ligand through the ester-type carboxylate and the deprotonated thiolate group was retained in solution. DFT (Density Functional Theory) study confirmed the proposed structures in solution phase as well as the determination of the most probable stable ring conformation. Biological investigations showed that Bu₂SnCl₂ and NAC2 induce loss of viability in HCC cells and only moderate effects in non-tumor Chang liver cells. NAC2 showed lower cytotoxic activity than Bu₂SnCl₂, suggesting that the binding with NAC²⁻ modulates the marked cytotoxic activity exerted by Bu₂SnCl₂. Therefore, these novel butyl derivatives could represent a new class of anticancer drugs.     

Synthesis and antitumor activity of a new mixed-ligand complex di-n-butyl-(4-chlorobenzohydroxamato)tin(IV) chloride

Reaction of di-n-butyltin(IV) dichloride with 4-chlorobenzohydroxamic acid at 1:1 ratio yielded a new mixed-ligand diorganotin(IV) complex, di-n-butyl-(4-chlorobenzohydroxamato)tin(IV) chloride(DBDCT). It was fully characterized by IR, ¹H, ¹³C, ¹¹⁹Sn NMR spectra and single crystal X-ray analysis. In DBDCT, the tin atom is five-coordinated in a trigonal bipyramidal geometry. DBDCT exhibited strong in vitro cytotoxic activity toward human immature granulocyte leukemia (HL-60), human salivary-gland carcinoma (SGC-7901), human henrietta carcinoma (Hela) and human urinary bladder (T24) cell lines which, in some cases, were equal to, or even higher than those of cis-dichlorodiammineplatinum(II) (cisplatin, DDP), the widely clinically used drug. The further in vivo antitumor tests of DBDCT towards the transplantation tumor models of sarcoma carcinoma (S₁₈₀), hepatocellular carcinoma (H₂₂) and Ehrlich’s ascites carcinoma (EAC) on mice were carried out via injection intraperitoneally with cisplatin as positive contrast drug. The results showed that DBDCT displayed in vivo antitumor activity against the hepatocellular carcinoma H₂₂ and sarcoma carcinoma S₁₈₀ which were close to those of cisplatin, meanwhile, the survival-extending rates at middle dose and high dose on mice Ehrlich’s ascites tumor EAC were higher than those of cisplatin, and there was a good dose-effect relationship.     

Syntheses and crystal structures of three diorganoltin(IV) macrocycles

Three novel macrocyclic diorganotin(IV) compounds of the type: {[R₁₀(SnO)₃(SnOH)₂]H_nXO_m}₂ · L (n=1, m=4, R=PhCH₂, X=P, L=0, 1; n=0, m=4, R=PhCH₂, X=S, L=4H₂O, 2; n=0, m=3, R=n-Bu, X=N, L=0, 3) were synthesized by the reaction of (PhCH₂)₂SnCl₂ with Na₂H_nXO₄ (n=1, X=P; n=0, X=S) or (n-Bu)₂SnCl₂ with NaNO₃. All the compounds 1, 2 and 3 are characterized by elemental, IR and X-ray diffraction analyses. X-ray data reveal that a macrocyclic structure with two centrosymmetric ladders of hydrolysis exists in the crystals of the three compounds. The geometry about each tin atom involved is trigonal bipyramidal.     

Synthesis, structures and properties of dinuclear cadmium(II) complexes based on polybenzimidazole binucleating ligands

Three novel cadmium(II) complexes [Cd₂(tbpo)(O₂CC₆H₄-p-NO₂)₂]ClO₄·3CH₃OH (1) [Cd₂(bbap)(O₂CC₆H₄-p-NO₂)₂]ClO₄·4.5CH₃OH·0.75H₂O (2) and [Cd(ntb)(O₂CC₆H₄-p-NO₂)]ClO₄·4CH₃OH (3) have been synthesized and characterized by IR, elemental analysis, ¹H NMR and X-ray crystallography, where tbpo⁻ and bbap⁻ are anions of N,N,N′,N′-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane and 2,6-bis[bis(2-benzimidazolylmethyl)aminomethyl]-4-methylphenol, respectively; ntb is tris(2-benzimidazolymethyl)amine. Complexes 1 and 2 contain μ-phenolate-bridged and μ-alkoxo-bridged dicadmium(II) cores with the Cd1?Cd2 separation of 3.671 Å for complex 1 and 3.718 Å for 2. One of the 4-nitrobenzoate anions bridged the two cadmium(II) ions in syn-anti mode through its carboxylate group, the other 4-nitrobenzoate is only coordinated with Cd2 in bidentate chelating mode. The two central cadmium(II) atoms are in trigonal bipyramidal and pentagonal bipyramidal geometry. In complex 3, the cadmium(II) atom is coordinated with four nitrogen atoms of ntb and one carboxylate oxygen atom of 4-nitrobenzoate in distorted trigonal bipyramidal geometry. Experiment shows that there is a higher affinity of 4-nitrobenzoate anion as coligand with the dinuclear [Cd₂(tbpo)]³⁺ and [Cd₂(bbap)]³⁺ cores than that with the mononuclear [Cd(ntb)]²⁺ core.     

Synthesis, characterization, crystal structures and in vitro antistaphylococcal activity of organotin(IV) derivatives with 5,7-disubstituted-1,2,4-triazolo[1,5-a]pyrimidine

New organotin(IV) complexes of 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine (dbtp) and 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine (dptp) with 1:1 and/or 1:2 stoichiometry were synthesized and investigated by X-ray diffraction, FT-IR and ¹¹⁹Sn Mössbauer in the solid state and by ¹H and ¹³C NMR spectroscopy, in solution. Moreover, the crystal and molecular structures of Et₂SnCl₂(dbtp)₂ and Ph₂SnCl₂(EtOH)₂(dptp)₂ are reported. The complexes contain hexacoordinated tin atoms: in Et₂SnCl₂(dbtp)₂ two 5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine molecules coordinate classically the tin atom through N(3) atom and the coordination around the tin atom shows a skew trapezoidal structure with axial ethyl groups. In Ph₂SnCl₂(EtOH)₂(dptp)₂ two ethanol molecules coordinate tin through the oxygen atom and the 5,7-diphenyl-1,2,4-triazolo[1,5-a]pyrimidine molecules are not directly bound to the metal center but strictly H-bonded, through N(3), to the OH group of the ethanol moieties; Ph₂SnCl₂(EtOH)₂(dptp)₂ has an all-trans structure and the C-Sn-C fragment is linear. On the basis of Mössbauer data, the 1:2 diorganotin(IV) complexes are advanced to have the same structure of Et₂SnCl₂(dbtp)₂, while Me₂SnCl₂(dptp)₂ to have a regular all-trans octahedral structure. A distorted cis-R₂ trigonal bipyramidal structure is assigned to 1:1 diorganotin(IV) complexes. The in vitro antibacterial activities of the synthesized complexes have been tested against a group of reference pathogen micro-organisms and some of them resulted active with MIC values of 5 μg/mL, most of all against staphylococcal strains, which shows their inhibitory effect.     

Study of complex formation with 2-hydroxyiminocarboxylates: specific metal binding ability of 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid

Complex formation properties of a novel water soluble thiazolyloxime 2-(4-methylthiazol-2-yl)-2-(hydroxyimino)acetic acid (H₃L¹) with Cu²⁺ and Ni²⁺ were investigated in solution by potentiometrical and spectral (UV-Vis, EPR, NMR) methods. All Cu²⁺ and most of Ni²⁺ complex species detected in solution were found to have square-planar MN₄ core with oxime and heterocyclic nitrogen atoms which was rationalized in terms of destabilizing effect of repulsive interaction between oxygen atom of carboxylic group and nitrogen atom of thiazole ring in N,O-coordinated ligand conformation. It has been found that stability of metal complexes in a series of oxime ligands is dependent upon basicity of nitrogen atom of oxime group. The thiazolyloxime forms less stable complexes with Cu²⁺ but stronger ones with Ni²⁺ ions when compared to parent 2-(hydroxyimino)propanoic acid. The lower stability obtained for Cu²⁺ complexes was elucidated in terms of negative inductive effect of the thiazole and nitrile substituents as well as an effect of intramolecular attractive interaction between thiazolyl sulfur and oxime oxygen atoms in thiazolyloxime. In the case of Ni²⁺ the complexes formed are square-planar and it is why thiazolyl ligand is more effective in metal ion binding than simple 2-(hydroxyimino)propanoic acid forming only octahedral species. The solid state structure of the Co³⁺ complex K₃[Co(HL¹)₃]·5.5H₂O (1) was studied by X-ray analysis. The thiazolyloxime ligand is coordinated to Co³⁺ via oxime nitrogen and carboxylate oxygen atoms forming five-membered chelate rings.     

119Sn Mössbauer spectroscopic studies of the products of the reaction of triorganotin(IV) derivatives with 6-thiopurine

A structural study of the products of the reaction of R₃Sn^IV derivatives (R = Me, Buⁿ, Ph) with 6-thiopurine, 6-TPH₂, and its sodium salt, 6-TPHNa, has been undertaken using Mössbauer spectroscopy and the point-charge model rationalization of the Mössbauer parameter nuclear quadrupole splitting. The synthetic reactions have been carried out at ca. 0 °C, 20 °C and 50 °C. The Mössbauer spectra of the complexes AlK₃Sn(6-TPH) are consistent with the occurrence of two distinct tin(IV) sites in samples prepared at the lower temperature, while one only site appears by increasing the temperature of the reaction. Two tin sites constantly occur in the products of the reactions involving the Ph₃Sn^IV moiety; the stoichiometry is assumed to be (Ph₃Sn)₃(6-TPH)(6-TP) for the uniquely-formed complex. Solid state polymeric structures with trigonal bipyramidal environments of the tin atoms and planar SnC₃ skeletons have been proposed. The apical ligand atoms have been assumed to be N, S and N, N in the samples showing two individual tin(IV) sites, and N, N when a single site was present.     

Synthesis, spectroscopic characterization, and crystal structures of two chlorodiorganotin(IV) 4-(2-methoxyphenyl)piperazine-1-carbodithioates

Two chlorodiorganotin(IV) complexes of 4-(2-methoxyphenyl)piperazine-1-carbodithioate (MPPDA) have been synthesized by 1:1 mole-ratio reactions of the parent acid (MPPDAH) with Me₂SnCl₂ or Et₂SnCl₂ in dry methanol. The products have been characterized by Raman and multinuclear NMR (¹H, ¹³C and ¹¹⁹Sn) spectroscopy, elemental analysis, and mass spectrometry. Single-crystal X-ray diffraction studies indicate that both complexes have distorted trigonal bipyramidal geometries around the central Sn atom.     

Imidazole-containing ternary complexes of N-benzyloxycarbonyl-aminoacids. Crystal and molecular structure of bis(N-benzyloxycarbonyl-alaninato)bis-(N-methylimidazole)copper(II) ethanol solvate

Mixed ligand complexes of the type Cu(Z-aminoacidato)₂(B₂) (Z = benzyloxycarbonyl group, Z-aminoacidate = Z-glycinate (Zgly), Z-alaninate (Zala); Z-valinate (Zval), Z-leucinate (Zleu) ion, B = imidazole (Im), N-methylimidazole (MeIm)) were synthesized and characterized by means of electronic, infrared and EPR spectroscopies. For one of them, bis(Z-alaninato)bis(N-methylimidazole)copper(II) ethanol solvate, the crystal and molecular structure was also determined by the single crystal X-ray diffraction method. The complex crystallizes in the monoclinic space group P2₁/c, with cell dimensions a = 11.1119(6), b = 18.8398(7), c = 8.9652(5) Å, β = 105.380(2)° and Z = 2. The structure was solved by conventional Patterson and Fourier methods and refined by full-matrix least-squares to an R value of 0.045. The complex has square-planar coordination via two centrosymmetric carboxylic oxygens and two N-methylimidazole nitrogens. The second carboxylate oxygen is 2.731(5) Å from the copper atom in an ‘out of plane’ position. Packing is mainly determined by hydrogen bondings between amide nitrogen and amide carboxyl oxygen. Electronic, infrared and EPR spectra are consistent with this type of coordination geometry for anhydrous complexes, while for hydrate complexes are suggestive of tetragonal bipyramidal geometry.     

Studies on dithio-o-toluate copper(I) complexes with bis(diphenylphosphino)methane. Crystal structures of {di-μ3-dithio-o-toluato-S,S′,S′-bis[μ-bis(diphenylphosphino)methane-μ-dithio-o-toluato-S,S′]} tetracopper(I) and {di[μ-bis(diphenylphosphino)methane]bis(dithio-o-toluato-S,S′)} dicopper(I)

The structures of [(CuS₂CT)₂dppm]₂ (I) (T = o-tolyl; dppm = bis(diphenylphosphino)methane) and [CuS₂CTdppm]₂ (II) have been determined by X-ray methods. Crystals of I are monoclinic, space group P2₁/n, with a = 15.163(4), b = 18.691(5), c = 13.478(4) Å, β = 96.81(3)°, Z = 2; crystals of II are orthorhombic. space group Pccn, with a = 23.267(4), b = 13.016(3), c = 20.731(5) Å, Z = 4. The structures of I and II have been solved by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.082 for I and 0.092 for II. The structure of I consists of centrosymmetric tetranuclear complexes in which two pairs of Cu atoms are triply bridged by a dppm ligand and two dithiocarboxylate groups from the dithio-o-toluate ligands. These last behave differently: one of them through a sulphur atom is also bonded to a Cu atom of the other pair so forming a tetranuclear complex. The Cu atoms of each pair show different coordination: Cu(1) displays a distorted trigonal and Cu(2) a distorted trigonal pyramidal geometry. The structure of II consists of dimers, in which each copper atom, doubly bridged by two dppm ligands, completes a distorted trigonal pyramidal coordination through two sulphur atoms from dithio-o-toluate anions acting as chelating ligands. In both compounds the phenyl group of the dithio-o-toluate anions is orthogonal to the corresponding CS₂ group. Both complexes give methyldithio-o-toluate in high yields by reaction with methyl iodide.     

Synthesis and characterization of new chromium(III), vanadium(IV), and titanium(III) complexes with biologically active isonicotinic acid hydrazide

New complexes of the type [Cr(INH)2Cl2]Cl.2H2O, VO(INH)2Cl2 and TiO(INH)2Cl, where INH = isonicotinic acid hydrazide, have been prepared. The complexes were characterized by infrared and UV-vis spectroscopy, proton nuclear magnetic resonance (NMR) and elemental analyses, molar conductivity and x-ray powder diffraction measurements. For the Cr(III)-complex, the ligand was coordinated through its carbonyl group and amino nitrogen atom; for V(IV)-complex and Ti(III)-complex, the ligand was coordinated through its carbonyl oxygen and heterocyclic nitrogen, respectively. Octahedral geometry has been proposed for all the complexes. The complexes of Cr(III) and Ti(III) showed significant tuberculostatic activity.     

Synthesis and X-ray crystal structures of organotri(2-furyl)phosphonium salts: effects of 2-furyl substituents at phosphorus on intramolecular nitrogen to phosphorus hypervalent coordinative interactions

The synthesis of tri(2-furyl)(8-quinolylmethyl)phosphonium bromide and 2-[2-tri(2-furyl)phosphoniophenyl]benzimidazole perchlorate is described, the latter involving a nickel(II)-catalysed displacement of bromine from 2-(2-bromophenyl)benzimidazole by tri(2-furyl)phosphine. X-ray structural studies of the phosphoniobenzimidazole salt reveals the existence of a significant hypervalent coordinative interaction between heterocyclic nitrogen and the phosphonium centre, which also appears to be retained in solution, the ³¹P NMR spectrum showing a significantly shielded phosphorus atom, δ³¹P=ca. 40 ppm in CDCl₃. The structure of the phosphoniophenylbenzimidazole cation reveals major distortion of bond angles about phosphorus away from the idealised tetrahedral angles expected for a tetraarylphosphonium salt, in the range 102-116°. Three of the angles are reduced below the tetrahedral angle and three are increased, the structure about phosphorus approaching that of a trigonal bipyramid, in which the heterocyclic imino nitrogen forms part of a five-membered ring spanning apical-equatorial positions. The apical axis of the trigonal bipyramid is formed by this nitrogen atom and one of the 2-furyl groups, the apical axial bond angle (N2-P-C14) being an average of 178°. The remaining 2-furyl groups occupy equatorial positions, along with the phenyl ring. Significantly, the nitrogen-phosphorus distance is an average of 2.67 Å (for two independent molecules in the unit cell), being the shortest observed in structures of this type, a consequence of the electron-withdrawing properties of the 2-furyl substituents at phosphorus. The structure also shows edge to face associations of 2-furyl substituents of one cation with the phenyl ring of the benzimidazole unit of another cation. The perchlorate anion is hydrogen-bonded to the nitrogen bearing the hydrogen atom in the benzimidazole ring system. In contrast, the N-P interaction in the quinolylmethylphosphonium salt is much less developed, with an N-P distance of 3.511 Å, although there is considerable deformation of bond angles at phosphorus. The crystal structure is dominated by the existence of hydrogen-bonded interactions between the cation, anion and a molecule of water, and by face to face interactions between cations. Both salts undergo loss of a 2-furyl group on treatment with hydroxide ion.     

Structural investigations on diorganotin and triorganotin(IV) phosphomycin derivatives

Four new diorganotin(IV), (R = Me, Bu), and triorganotin(IV), (R = Me, Ph), derivatives of the phosphomycin disodium salt antibiotic[(1R,2S)-1,2-epoxypropylphosphonate]Na₂ have been synthesized and their solid state configuration studied by X-ray crystallography, FT-IR, Mössbauer, UV-Vis spectroscopies. The X-ray diffraction investigation, performed on the bis[trimethyltin(IV)]phosphomycin, showed that the coordination geometry at all the Sn atoms is trigonal bipyramidal. The structure of the complex forms an unusual polymeric zig-zag planar network. The FT-IR and the ¹¹⁹Sn Mössbauer studies supported the formation of trigonal bipyramidal (Tbp) molecular structures, both in the diorganotin(IV) and triorganotin(IV) derivatives, even if, in the case of diorganotin(IV) derivatives, the tetrahedral structure cannot be a priori excluded. The group of phosphomycin coordinates the organotin(IV) centers originating a monodimensional polymeric network, as inferred by variable temperature ¹¹⁹Sn Mössbauer spectroscopy, used to investigate lattice dynamics of the bis-[trimethyltin(IV)]phosphomycin complex.     

The local structure of solid diorganotin(IV) complexes formed with carbohydrates by X-ray absorption spectroscopy

Diethyltin(IV) complexes formed with carbohydrate ligands (aldoses, polyalcohols, sugar acids and disaccharides) containing the diethyltin(IV) moiety and the carbohydrate ligand in a 1:1 ratio were prepared. Their local structures were determined by extended X-ray absorption fine structure (EXAFS) in the solid state. The results showed that the dioxastannolane units are associated into an infinite chain polymer, in which tin(IV) is bound by two carbon atoms and three or four oxygen atoms either in highly distorted octahedral and trigonal bipyramidal arrangements or in a purely trigonal bipyramidal arrangement. The present structure models are consistent with the results of previous Mössbauer studies, proving the advantages of the use of the partial quadrupole splitting concept for the determination of the symmetry of the coordination sphere in tin(IV) organic complexes.     

Di- and triorganotin(IV) carboxylates derived from triorganotin(IV) iodide with mixed organic groups on tin: Cyclic, hexameric triorganotin(IV) carboxylates

The reaction of ethyldiphenyltin(IV) iodide with silver benzoate in ethanol results in the formation of bis(benzoato)ethylphenyltin(IV), EtPhSn[OC(O)C₆H₅]₂ (1), by the cleavage of a phenyl group bound to tin. The reaction of ethyldiphenyltin(IV) iodide with silver acetate provides acetatoethyldiphenyltin(IV), EtPh₂SnOC(O)CH₃ (2). Similarly, the reaction of diphenylpropyltin(IV) iodide with silver acetate affords acetatodiphenyl-n-propyltin(IV), Ph₂PrSnOC(O)CH₃ (3). These three complexes were characterized by elemental analysis, mass spectrometry, and infrared spectroscopy (IR), as well as ¹H, ¹³C, and ¹¹⁹Sn NMR. The molecular structures of three complexes were also verified by single-crystal X-ray analyses. The X-ray structures show that 1 adopts a skew-trapezoidal bipyramidal structure, while 2 and 3 are rare, cyclic hexameric structures.     

Hydrothermal syntheses, structural characterizations and magnetic properties of cobalt(II) and manganese(II) coordination polymeric complexes containing pyrazinecarboxylate ligand

Two novel coordination polymeric complexes [Co(pzca)₂(H₂O)]_n (1) and [Mn(pzca)₂]_n (2) (pzca=2-pyrazinecarboxylate) have been synthesized by hydrothermal reaction of M(CH₃COO)₂·4H₂O (M=Co, Mn) and 2-pyrazinecarboxylic acid. The complex 1 displays an infinite zigzag chain structure in which each cobalt(II) center was coordinated by three nitrogen and three oxygen atoms to generate a CoN₃O₃ octahedral geometry. The existence of hydrogen bond leads to the formation of the interpenetrating stacking structure. Complex 2 indicates a two-dimensional layer structure through the linkage of bridging oxygen atom of pzca ligand. Each Mn(II) center exhibits a distorted octahedral coordination environment with four oxygen atoms and two nitrogen atoms. The distances of adjacent Mn(II) atoms are 3.503 and 5.654 Å, respectively. The magnetic property analyses reveal that both complexes show weak antiferromagnetic exchange interactions between the metal centers.