Tetrahedral Stereochemistry Research Articles

Synthesis and Structural Views on New Azo Ligand and Its Metal Complexes with Some of their Application

In this work, we presented a study of the structural formula for a new series of complexes with Ag(I), Cu(II), Zn(II), and Cd(II) derived from the guanine azo dye ligand 2-amino-8-((3-hydroxyphenyl)diazinyl)-1,7-dihydro-6H-purin-6-one (HAG), which is investigated using various physicochemical analyses, spectroscopic techniques (FT-IR, U.V-VIS, and 1H NMR), thermogravimetric analysis (TGA). In addition, elemental analyses, magnetic susceptibility, and molar conductance measurements were all stabilized. As well as the mole ratio, stability constant, and Gibbs free energy were studied for all complexes, where they showed high stability and spontaneous synthesis. The Cu(II) complex was suggested to have octahedral stereochemistry, while the Ag(I), Zn(II), and Cd(II) complexes were suggested to have tetrahedral stereochemistry. The ligand has been demonstrated to be a useful acid-base indicator, and it has been shown that the ligand (HAG) and its complexes exhibit high photostability and have various colors that can be used to dye wool materials.

Insights into Structure and Biological Activity of Copper(II) and Zinc(II) Complexes with Triazolopyrimidine Ligands.

In an attempt to increase the biological activity of the 1,2,4-triazolo[1,5-a]pyrimidine scaffold through complexation with essential metal ions, the complexes trans-[Cu(mptp)2Cl2] (1), [Zn(mptp)Cl2(DMSO)] (2) (mptp: 5-methyl-7-phenyl-1,2,4-triazolo[1,5-a]pyrimidine), [Cu2(dmtp)4Cl4]·2H2O (3) and [Zn(dmtp)2Cl2] (4) (dmtp: 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine), were synthesized and characterized as new antiproliferative and antimicrobial species. Both complexes (1) and (2) crystallize in the P21/n monoclinic space group, with the tetrahedral surroundings generating a square-planar stereochemistry in the Cu(II) complex and a tetrahedral stereochemistry in the Zn(II) species. The mononuclear units are interconnected in a supramolecular network through π–π interactions between the pyrimidine moiety and the phenyl ring in (1) while supramolecular chains resulting from C-H∙∙∙π interactions were observed in (2). All complexes exhibit an antiproliferative effect against B16 tumor cells and improved antibacterial and antifungal activities compared to the free ligands. Complex (3) displays the best antimicrobial activity against all four tested strains, both in the planktonic and biofilm-embedded states, which can be correlated to its stronger DNA-binding and nuclease-activity traits.

On the centennials of the discoveries of the hydrogen bond and the structure of the water molecule: the short life and work of Eustace Jean Cuy (1897-1925).

The bent structure of the water molecule, and its hydrogen-bonding properties, arguably rank among the most impactful discoveries in the history of chemistry. Although the fact that the H-O-H angle must deviate from linearity was inferred early in the 20th century, notably from the existence of the electric dipole moment, it was not clear what that angle should be and why. One hundred years ago, a young PhD student at the University of California, Berkeley, Eustace J. Cuy, rationalized the V-shape structure of a water molecule using the Lewis theory of a chemical bond, i.e. a shared electron pair, and its tetrahedral stereochemistry. He was inspired, in part, by the proposal of a weak (hydrogen) bond in water by two colleagues at Berkeley, Wendell Latimer and Worth Rodebush, who published their classic paper a year earlier. Cuy went on to suggest that other molecules, notably H2S and NH3, have similar structures, and presciently predicted that this architecture has broader consequences for the structure of water as a liquid. This short, but brilliant paper has been completely forgotten, perhaps due to the tragic death of the author at the age of 28; the hydrogen-bond study is also rarely recognized. One of the most impactful publications on the structure of liquid water, a classic treatise published in 1933 by John Bernal and Ralph Fowler, does not mention either of the two pioneering papers. In this essay, the background for the two discoveries is described, including the brief history of Lewis's research on the nature of the chemical bond, and the history of the discovery of the hydrogen bond, which inspired Cuy to look at the structure of the water molecule. This is - to the best of the author's knowledge - the first biographical sketch of Eustace J. Cuy.

Spectral characterization, DFT, docking and cytotoxicity of N-benzyl-4,5-dihydro-3-methyl-5-oxo-1H-pyrazole-4-carbothioamide and its metal complexes

A new ligand N-benzyl-4,5-dihydro-3-methyl-5-oxo-1H-pyrazole-4-carbothioamide (H2L) and some of its divalent metal complexes were synthesized. Elemental analyses, mass spectra (MS), 1H and 13Cnuclear magnetic resonance, electronparamagnetic resonance (EPR), infrared spectra (IR), ultra-violet and visible spectra, thermogravimetric analyses (TGA) and the effective magnetic moments were used in characterization of the isolated compounds. The ligand (H2L) was geometry optimized by density function theory. The vibrational spectra of the optimized H2L was calculated and compared with the observed spectra. There was a good agreement between the theoretically calculated and the experimental vibrational spectra. Tetrahedral stereochemistries were suggested for Co(II), Ni(II) and Zn(II) complexes while, square planar stereochemistry was suggested for Cu(II) complex. Molecular docking was carried out to indicate the interaction between the tested compounds and the studied protein. Molecular docking was able to predict the anticancer activities of the ligand and its complexes.The cytotoxicity of the ligand and its complexes was tested on Helacell line. The ligand showed strong cytotoxicity while, the metal complexes had moderate.

Binary and ternary Cu(II) complexes of pregabalin with excitatory and inhibitory neurotransmitters and their antiepileptic effect.

Antiepileptic drug (Preg) and neurotransmitters (Gpn, Gly, Asp, Glu, Ser, GABA and Ade) were used to synthesis a series of ternary Cu2+ complexes. Surface morphology and chemical composition of the complexes were using studied SEM and EDX spectra. Purity, molecular weight and formulae of the complexes were determined from GC-MS spectra and elemental analysis. XRD data and N-Treor implemented in Expo2014 computer program reveal monoclinic crystal system with space group P1 2/c 1 and P 1 21 1 of the complexes. IR spectra exhibited that Preg, Gpn and GABA coordinated to the Cu2+ as monodentate ligand through COOH whereas the amino acids bonded through the -NH2, COO- groups. UV-Vis spectra and magnetic moment values indicated pseudo tetrahedral stereochemistry. ESR spectra showed that the complexes have isotropic and axial structures with dx2-y2 ground state. TGA, DTG and DTA confirm the suggested structure and mechanism for thermal decomposition was suggested. Kinetic and thermodynamic parameters were calculated using Coats-Redfern equation. The complexes [Cu(Preg)(Ser)Cl] and [Cu(Preg)(Ade)Cl2] showed greater anticonvulsant activity compared against PTZ-induced seizures in male Albino mice. Recorded latency time for the complexes [Cu(Preg)(Ser)Cl] and [Cu(Preg)(GABA)(OH)Cl].2H2O was longer than that recorded with Preg indicating higher anticonvulsant effect.

Copper(II) ternary complexes with gabapentin and neurotransmitters as antiepileptic drug

Novel series of ternary complexes of Cu2+ with antiepileptic drug (Gpn) and neurotransmitters (Gly, Asp, Glu, Ser, GABA and Ade) were synthesized. Surface morphology of the complexes and their chemical composition were studied using elemental analysis, SEM and EDX spectrum. Majority of the complexes were non-electrolytes. Molecular weight and purity was confirmed using GC-MS spectrum. Crystallographic parameters were calculated for the complexes from their XRD data using Expo2014 computer program showing monoclinic and orthorhombic crystal systems with space group P 1 21 1 and P 2 21 21. Crystal structural data, UV–Vis spectra and magnetic moment values indicate distorted square planar and pseudo tetrahedral stereochemistry. IR data reveal that Cu2+ is bonded through COOH of the Gpn and NH2, COO− of the amino acids. ESR spectra showed dx2‒y2 ground state for the Cu2+. TGA, DTG, DTA and the suggested decomposition mechanism confirm the proposed structure of the complexes. The complexes [Cu(Gpn)(Asp)(H2O)].5H2O, [Cu(Gpn)(Ser)Cl] and [Cu(Gpn)(Ade)Cl2].5H2O showed superior anticonvulsant activity compared to gabapentin since they significantly reduced the seizure score compared to PTZ group in male Albino mice. Also, the complex [Cu(Gpn)(Asp)(H2O)].5H2O was the only that markedly prolonged the latency time compared to Gpn group.

Crystal structure of bis[tetrakis(tetrahydrofuran-κO)lithium] bis[μ-2,2′,2′′-methanetriyltris(4,6-di-tert-butylphenolato)-κ4O,O′:O′,O′′]dimagnesiate

The title ion-association metal complex, [Li(C4H8O)4]2[Mg2(C43H61O3)2], has been synthesized from the tridentate phenolic ligand tris-(3,5-di-tert-butyl-2-hy-droxy-phen-yl)methane in tetra-hydro-furan (THF). The aryl-oxo magnesiate complex anion is binuclear with each Mg2O4 complex unit inversion-related and bridged through the two tridentate chelating phenolate O-donors of the ligand. The complex centres have a distorted tetra-hedral stereochemistry [Mg-O range 1.8796 (17)-2.0005 (16) Å] and an Mg⋯Mg separation of 2.9430 (14) Å]. The LiO4 coodination sphere of the cation comprises four THF O-donor atoms and has a slightly distorted tetra-hedral conformation [Li-O range 1.899 (5)- 1.953 (5) Å]. In the crystal, a number of stabilizing intra-anion C-H⋯O hydrogen-bonding inter-actions are present but no inter-species associations are found.

Nickel(II)-oxaloyldihydrazone complexes: Characterization, indirect band gap energy and antimicrobial evaluation

AbstractA series of oxaloyldihydrazone ligands was prepared essentially by the usual condensation reaction between oxaloyldihydrazide and different aldehydes e.g. salicylaldehyde, 2-hydroxy-1-naphthaldehyde, 2-hydroxyacetophenone and 2-methoxy-benzaldehyde in 1:2 M ratio. The formed compounds were purified to give bis(salicylaldehyde)oxaloyldihydrazone (L1), bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone (L2), bis(2-hydroxyacetophenone)oxaloyldihydrazone(L3) and bis(2-methoxy-benzaldehyde)oxaloyldihydrazone (L4). All the oxaloyldihydrazones (L1–L4) and their relevant solid nickel(II) complexes have been prepared and structurally characterized on the basis of the elemental analyses, spectral (UV–vis, IR, mass and 1H NMR), magnetism and thermal (TG) measurements. The dihydrazones coordinate to the metal center forming mononuclear complexes with L1, L3 and L4 in addition to binuclear complex with L2. The metal center prefers tetrahedral stereochemistry upon chelation. The optical indirect band gap energy ...

Structural and theoretical study of six dinuclear Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) complexes containing ON-NO donor azodye ligand, 4,4’-(1E,1’E)-(5,5’-(propane- 2,2-diyl)bis(2-hydroxy-5,1-phenylene)bis(diazene-2,1-diyl)dibenzenesulfonic a

Six dimeric transitional metal complexes with ON-NO donor bis-bidentate azodye ligand 4,4’-(1E,1’E)-(5,5’-(propane-2,2-diyl)bis(2-hydroxy-5,1-phenylene)bis(diazene-2,1-diyl)dibenzenesulfonic acid (PDHPDDDBSA) have been synthesised and characterized by elemental, analytical, conductivity measurement, magnetic moments, spectral, thermal, X-ray diffraction (powder pattern) and theoretical methods. The Co(II) and Ni(II) complexes are found to be octahedral, Cu(II) complex is distorted-octahedral and a tetrahedral stereochemistry has been suggested to Zn(II), Cd(II) and Hg(II) complexes. The thermal analysis data provided the kinetic parameters as order of decomposition reaction, activation energy and frequency factor. All theoretical calculations of the ligand and the Cu(II) and Zn(II) complexes were made using Gaussian 03 rev. A.01 programme package hybrid DFT/B3LYP hybrid functional level of theory with LANL2DZ basic set for copper and zinc atoms in gas phase and 6-31 G(d,p) basic set for other atoms. The DFT study of the ligand and the complexes is used to calculate the bond length, bond angle, HOMO, LUMO and dipole moment values. The calculated HOMO-LUMO energy gap shows that a charge transfer occurs within the molecule. The Cd(II) complex is found to have an orthorhombic crystal system. KEY WORDS: Azodye complexes, Thermogravimetric study, Theoretical study (DFT/B3LYP) Bull. Chem. Soc. Ethiop. 2016, 30(1), 87-100. DOI: http://dx.doi.org/10.4314/bcse.v30i1.8

Synthesis, characterisation, spectral, thermal, XRD, molecular modelling and potential antibacterial study of metal complexes containing octadentate azodye ligands

Twelve tetrametallic complexes of Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) with two new octadentate azodye ligands, 4,4′-bis(2′,4′-dihydroxy-5′carboxyphenylazo) diphenylether (LH6) and 4,4′-bis(2′,4′-dihydroxy-5′-acylphenylazo) diphenylether (L′H4) have been synthesised. The structural elucidation of the complexes was made basing upon analytical, conductance, magnetic susceptibility, IR, electronic spectra, ESR, NMR, ESI-MS, TG, DTG, DTA and X-ray diffraction (powder pattern) data. The cobalt (II) and nickel (II) complexes are found to be octahedral, copper (II) complexes are distorted octahedral and a tetrahedral stereochemistry has been suggested to zinc (II), cadmium (II) and mercury (II) complexes. The thermal analysis data provided the kinetic parameters as order of decomposition reaction, activation energy and frequency factor. The geometry of the ligands and their Co(II), Ni(II), Cu(II) and Zn(II) complexes were optimised and their physicochemical properties were calculated by using molecular modelling procedure. The ESI-MS determination supports the molecular formula and molecular weight of the ligands and the complexes. The Ni(II) complex is found to have a triclinic crystal system. The potential antibacterial study of the two ligands and eight metal complexes was made by cup-plate method against one gram positive and one gram negative bacteria. The results showed increase in the activity of some metal complexes as compare with azodye ligands.

Chemical Synthesis, Spectral Characterization and Antimicrobial Studies on Complexes of Ni(II), Cu(II) and Zn(II) with N, N-di (o-hydroxybenzenoylmethylene) Ethylenediamine

The Schiff’s base ligands and their complexes with Ni(II), Cu(II) and Zn(II) were synthesized and characterized by elemental analysis molar conductivity, infrared and ultraviolet-visible spectroscopy and magnetic susceptibility measurements. The ligands, ethylenedianil of o-hydroxyphenylglyoxal, C18H16N2O4, have been synthesized by condensation of ethylenediamine and orthohydroxyphenylglyoxal. The metal complexes were prepared by mixing of saturated solutions of ligands and metal salts in appropriate molar ratio in acetone and methanol solvents. The study also confirmed the formation of mono-, di- and trinuclear isopolystructures of the complexes in square planar geometry except for Zn(II), which has tetrahedral stereochemistry. The synthesized ligands and their metal complexes were screened for their antimicrobial activities against two bacterial strains (Staphylococcus aureous and Xanthomonas holcicola), and two fungal strains (Aspergillus niger and Fusarium oxysporum) using a disc diffusion method. The tests showed that the complexes have higher antimicrobial activity than the free Schiff’s base.

Synthesis, characterization and electrochemical studies of heterometallic manganese(IV)–zinc(II) and manganese(IV)–copper(II) complexes derived from bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone

Five manganese(IV) complexes [Mn(L)(bpy)] (1) and heterobimetallic complexes [MMn(L)Cl2(H2O)4]·1.5H2O (M=ZnII(2), CuII(3)) and [MnM(L)(bpy)Cl2] (M=ZnII(4), CuII(5)] have been synthesized from bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone (H4L) in methanol medium. The composition of the complexes have been established based on the data obtained from analytical, thermoanalytical and mass spectral studies. The structures of the complexes have been discussed in the light of molar conductance, magnetic moment, electronic, EPR, IR, FT-IR spectroscopic studies and transmission electron microscopies. The molar conductance values of these complexes in DMSO suggest their non-electrolytic nature. The μeff value for the complexes (1), (2) and (4) fall in the range 3.82–4.12 BM characteristic of the presence of the manganese(IV) in them. The complex (3) has μeff value of 3.70 BM at RT indicating considerable antiferromagnetic interaction between Mn(IV) and Cu(II). The μeff value of 4.72 BM for complex (5) is slightly lower than 4.90 BM for S=2 ground state. In the complex (1) to (3), the ligand is coordinated to the metal centres as tetradentate ligand while in the complexes (4) and (5) as hexadentate ligand. Manganese(IV) has distorted octahedral stereochemistry in all complexes. Copper(II) has distorted octahedral and square planar stereochemistry in complexes (3) and (5) while zinc has distorted octahedral and tetrahedral stereochemistry, respectively. EPR studies of the complexes are also reported. The electron transfer reactions of the complexes have also been investigated by cyclic voltammetry.

Synthesis, characterisation, XRD, molecular modelling and potential antibacterial studies of Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) complexes with bidentate azodye ligand

Six monomeric complexes of Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) with one O N donor bidentate azodye ligand, 3 – (p-tolylazo) – 4 – hydroxyl – 5 – methoxybenzaldehyde (LH) (TAHMB) have been prepared. The complexes have been characterised by analytical, conductance, magnetic susceptibility, IR, electronic spectra, ESR, NMR, X-ray diffraction (Powder pattern) spectra and molecular modelling studies. The Co (II) and Ni (II) complexes are found to be octahedral, Cu(II) complex is distorted octahedral and a tetrahedral stereochemistry has been assigned to Zn(II), Cd(II) and Hg(II) complexes. The energy optimised structures Figs. 3–5 are proposed using the semi empirical ZINDO/1 quantum mechanical calculations. The Ni(II) complex is found to possess an orthorhombic crystal system. The potential antibacterial studies of the ligand and some metal complexes with gram positive and gram negative bacteria have given encouraging results.

Organoaluminum and ‐gallium Formamidinate Complexes

AbstractDialuminum formamidinate complexes [Me2Al(μ‐Form)(μ‐Me)AlMe2] [Form (ArNCHNAr) = EtForm (Ar = 2,6‐Et2C6H3) or DippForm (Ar = 2,6‐iPr2C6H3)] were obtained in good yields by treatment of formamidines (FormH) with trimethylaluminum in a 1:3 stoichiometry. The products contain both a bridging Form ligand and a bridging methyl group between the two aluminum centers. [M(Form)Me2] (M = Al, Form = DippForm, EtForm; M = Ga, Form = DippForm) were prepared in high yields by the protonolysis reactions of MMe3 (M = Al, Ga) with formamidines (FormH) in a 1:1 stoichiometry. [Al(DippForm)Me2] was also synthesized by other methods including concentration of the tetrahydrofuran/n‐hexane solution of [Me2Al(μ‐DippForm)(μ‐Me)AlMe2] to dryness and also by reaction of AlMe3 with [Ga(DippForm)Me2] in a 1:1 ratio. Partial dissociation of the dialuminum to monoaluminum complexes was detected in the 1H NMR spectra of [Me2Al(μ‐Form)(μ‐Me)AlMe2] complexes. All complexes exhibit a distorted tetrahedral stereochemistry of the Group 13 metal atoms.

Synthesis, Spectral, Thermogravimetric, XRD, Molecular Modelling and Potential Antibacterial Studies of Dimeric Complexes with Bis Bidentate ON–NO Donor Azo Dye Ligands

The dimeric complexes of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) with two new symmetrical ON–NO donor bis bidentate (tetradentate) azo dye ligands, LH2 = 4,4′‐bis(4′‐hydroxyquinolinolinylazo)diphenylsulphone, and L′H2 = 4,4′‐bis(acetoacetanilideazo)diphenylsulphone have been synthesized. The metal complexes have been characterised by elemental analytical, conductance, magnetic susceptibility, IR, electronic spectra, ESR, NMR, thermogravimetry, X‐ray diffraction (powder pattern) spectra, and molecular modelling studies. The Co(II) and Ni(II) complexes are found to be octahedral, Cu(II) complexes are distorted octahedral, and a tetrahedral stereochemistry has been assigned to Zn(II), Cd(II), and Hg(II) complexes. The thermogravimetric study indicates that compounds are quite stable. The energy optimized structures are proposed using the semiempirical ZINDO/1 quantum mechanical calculations. The potential antibacterial study of the ligands and some metal complexes has been made with one gram positive bacteria Staphylococcus aureus and one gram negative bacteria E. coli which gives encouraging results. Both the Co(II) complexes are found to possess monoclinic crystal system.

(RP)-5-Methyl-2-(propan-2-yl)cyclohexyl phenyl{phenyl[(1-phenylethyl)amino]methyl}phosphinate

In the title compound, C31H40NO2P, the P atom has a distorted tetra­hedral stereochemistry [bond-angle range about P = 103.33 (6)–115.24 (15)°] and has R P chirality, which was confirmed crystallographically. The dihedral angles between the P-bonded phenyl ring and the other two phenyl rings are 40.4 (3) and 12.2 (2)°. In the crystal, a C—H⋯O inter­action links mol­ecules into chains which extend along [100].

Bis(2-amino-5-methyl-1,3,4-thiadiazole-κN 3)dichloridocobalt(II)

In the monomeric title complex, [CoCl2(C3H5N3S)2], the CoII atom is tetra­coordinated by two chloride anions and two N atoms from two monodentate 2-amino-5-methyl-1,3,4-thia­diazole ligands, giving a slightly distorted tetra­hedral stereochemistry [bond angle range about Co = 105.16 (12)–112.50 (10)°]. In the complex, the dihedral angle between the 1,3,4-thia­diazole planes in the two ligands is 72.8 (1)°. There are two intra­molecular N—H⋯Cl inter­actions in the complex unit, while in the crystal, inter­molecular N—H⋯N and N—H⋯Cl hydrogen bonds link these units into a two-dimensional layered structure parallel to (011).

Spectral, magnetic and thermal characterisation of new Co(II), Ni(II) and Cu(II) complexes with Schiff base 5-bromo-N,N′-bis-(salicylidene)-o-tolidine

Starting from 5-bromo-N,N′-bis-(salicylidene)-o-tolidine (H2L) new complexes with Co(II), Ni(II) and Cu(II) were synthesised and characterised. The features of complexes have been assigned from microanalytical, IR, UV–Vis–NIR and EPR spectra, magnetic data at room temperature as well as thermal analysis. IR data are in accordance with bischelate nature of the deprotonated ligand that coordinates through azomethinic nitrogen and phenolic oxygen. The electronic spectra display the characteristic pattern of tetrahedral stereochemistry for [CoL]·H2O complex and octahedral one for [NiL(OH2)2]·H2O complex. The electronic spectra correlated with magnetic susceptibility measurements indicate a square-planar surrounding for [ML] (M:Ni, Cu) species, while the EPR spectrum of copper complex sustains the proposed stereochemistry. The thermal analysis evidenced that thermal transformations are complex processes according to TG, DTA and DTG curves including (crystallization or coordination) water elimination, thermolyses and oxidative degradation of Schiff base. All these processes lead to the most stable metallic oxides as final product.

Synthesis, spectral and thermal study on new Fe(III) complexes with N,N-dimethylbiguanide as antibacterial agents

New complexes [FeO(DMBG)]2 and [Fe(DMBG)2]Cl·0.5H2O (HDMBG: N,N-dimethylbiguanide) have been synthesized and characterized by microanalytical, IR and UV–Vis data. Electronic spectra of the complexes are characteristic for a tetrahedral stereochemistry, whilst the modifications in the IR spectra indicate the presence of the DMBG anion as chelate. The thermal decomposition investigated in air by thermal analysis confirmed the proposed formulas for the complexes and provided information concerning the modifications during heating and also the thermodynamic effects accompanying them. The thermal transformations are complex, according to TG and DTG curves including dehydration, hydrochloric acid elimination, oxidative degradation and condensation of –C=N– unit. The final product of decomposition was iron (III) oxide as powder XRD indicates. Complexes were screened for their antimicrobial properties against Gram-positive, Gram-negative bacterial, as well as fungal pathogenic strains. The results indicate that Fe(III) complexes exhibit an improved antibacterial activity against S. aureus and E. coli strains in comparison with free biguanide. The Fe(III) complexes also inhibit the ability of S. aureus, B. subtilis, P. aeruginosa and E. coli strains to colonize the inert substratum, accounting for their possible use as anti-biofilm agents.

Poly[tetra-n-butylammonium [(μ5-benzene-1,3,5-tricarboxylato)(μ4-benzene-1,3,5-tricarboxylato)-μ3-hydroxido-trizincate] 0.25-hydrate

In the asymmetric unit of title coordination polymer, {(C16H36N)[Zn3(C9H3O6)2(OH)]·0.25H2O}n, there are three independent Zn2+ cations, two benzene-1,3,5-tricarboxyl­ate ligands and a μ3-bridging hydroxide group, together with a tetra-n-butyl­ammonium counter-cation and a partially occupied water molecule of solvation (occupancy 0.25). Each Zn ion is coordinated by three carboxyl­ate O atoms and one O atom from the bridging hydroxide ion, displaying a slightly distorted tetra­hedral stereochemistry [overall Zn—O range = 1.875 (3)–1.987 (2) Å]. An intra­molecular hydrogen bond involving the hydroxide H atom and a carboxyl­ate O-atom acceptor is also present in the complex unit. The bridging benzene-1,3,5-tricarboxyl­ate anions generate a three-dimensional framework structure.