Dimeric Square Research Articles

Physico-chemical Characterization of Some Metal Complexes Formed by Substituted Thiourea

In view of unique physico-chemical observations affecting the geometry and various properties of the substituted thiourea complexes in literature along with several biological activities, N-(hydroxy)-N,N-diphenyl thiourea was taken up for study. Complexes with geometries of high spin octahedral for iron(II), cobalt(II); tetrahedral & square planar for nickel(II); and dimeric square planar for copper chloride, copper perchlorate, copper acetate and distorted octahedral for copper nitrate were synthesized and characterized based on magnetic moments, visible spectra, diffuse reflectance spectra, electron spin resonance, infrared spectral studies, and thermal analysis.
 Interestingly, the nature of anion influenced the geometry, the complex from copper nitrate salt resulted in a distorted octahedral structure and complexes formed from copper chloride, copper perchlorate, copper acetate exhibited sub-normal magnetic moments, highly insoluble in the most common organic solvents and water. Based on these and spectral data, polymeric or square-planar dimeric geometry with sulfur bridging between copper atoms is proposed. It was confirmed by the application of Bleaney-Bower’s equation for magnetic susceptibility, applicable to dimeric copper complexes.
 The overall thermal behavior of the ligand and complexes were observed and the detailed calculations interestingly lead to confirmation of the above proposed geometrical structures.

Syntheses, Characterization and Biological Activity of Coordination Compounds of Propanedioic Acid and its Mixed Ligand Complexes with N,N'-Dihydroxy-2,3-butanediimine

The coordination compounds of propanedioic acid with cobalt(II), nickel(II) and copper(II) ions were synthesized using metal:ligand 1:2. In addition to this, mixed ligand complexes using the same metal ions with propanedioic acid as the primary ligand and N,N'-dihydroxy-2,3-butanediimine as the secondary ligand were also synthesized using M:L1:L2 (1:1:1) where L1 = propanedioic acid, L2 = N,N'-dihydroxy-2,3-butanediimine and M = Cu(II), Ni(II) and Cu(II). The synthesized compounds were characterized using FTIR, UV-vis, magnetic susceptibility measurement and percentage metal composition. The ligand and its metal complexes were tested for their cytotoxic and antibacterial activities. Results indicated that a dimeric square planar geometry was assumed by the cobalt(II) and nickel(II) propanedioic acid complexes. Octahedral geometry was proposed for both cobalt(II) and copper(II) mixed ligand complexes. A dinuclear square pyramidal geometry was suggested for the copper(II) propanedioic acid complex and square planar/octahedral geometry for the nickel(II) mixed ligand complex. The copper(II) propanedioic acid complex elicited the best cytotoxic activity. On the other hand, the nickel(II) propanedioic acid complex showed the remarkable antimicrobial activity. The compounds exhibited good antimicrobial activity in most of the cases with the exception of the cobalt(II) propanedioic acid complex. It was concluded that coordination of the ligands to the metal ions lowered the toxicity of the ligands. It was further concluded that the antimicrobial activity of the compounds was partly dependent on the synergism/additive effect of the intrinsic therapeutic properties of the metal ion and the ligands within the coordination sphere of the complexes synthesized. And this is also in part a function of the geometry assumed by the complexes.

Syntheses, crystal structures and magnetism of azide-bridged five-coordinate binuclear nickel(II) and cobalt(II) complexes

The bulky ligand 2,9-dimethyl-1,10-phenanthroline (dmphen) has been used to construct pentacoordinate transition metal complexes. Two such doubly end-on azido-bridged dinuclear complexes [M2(dmphen)2(μ1,1−N3)2Cl2] [M = Ni (1) or M = Co (2)] have been obtained and characterized by single-crystal X-ray diffraction analysis and magnetic studies. Both complexes consist of dimeric square pyramidal M(II) centers bridged by two end-on azide ligands. Magnetic studies suggest that both complexes display intramolecular intermetallic ferromagnetic coupling. The coupling constants for pentacoordinate azide-bridged dinuclear Ni(II) complexes are found to decrease with the increasing Ni–N–Ni bond angle.

Axially chiral monomeric and dimeric square planar Pd(ii) complexes and their application to chiral tectonics

Mononuclear and dinuclear square planar palladium(II) complexes (denoted by [(hfac)Pd(II)(L-LH)] and [(hfac)Pd(II)(L-L)Pd(II)(hfac)], respectively) were synthesized. Here hfac(-), HL-L(-) and L-L(2-) denote hexafluoroacetylacetonato, monoprotonated and non-protonated bis-β-diketonato ligands, respectively. Three bis-β-diketones were used as HL-LH: 1,2-diacetyl-1,2-dibenzoylethane (denoted by dabeH2), 1,2-diacetyl-1,2-bis(3-methylbutanoyl)ethane (baetH2) and 1,2-diacetyl-1,2-propanoylethane (dpeH2). Both the monomeric and dimeric Pd(II) complexes were chiral due to the orthogonal twisting of the two non-symmetric diketonato moieties in HL-L(-) and L-L(2-), respectively. Optical resolution of [(hfac)Pd(II)(dabe)Pd(II)(hfac)] was achieved chromatographically on a chiral column to obtain a pair of optical antipodes which were stable against racemization. As for the other complexes, resolution was possible only after replacing hfac(-) with a bulky ligand such as dibenzoylmethanato (dbm(-)). Although a dinuclear complex with a symmetric bis-β-diketonato ligand, [(hfac)Pd(II)(taet)Pd(II)(hfac)] (taet(2-) = 1,1,2,2-tetraacetylethanato), was achiral, the replacement of the terminal ligands with non-symmetric β-diketonates yielded an axially chiral complex such as [(phacac)Pd(II)(taet)Pd(II)(phacac)], wherein phacac(-) denotes 1-phenyl-1,3-butanedionato. The UV and CD spectra of the Pd(II) complexes were analyzed with the help of the TDDFT calculations. The chiral monomeric species, [(dbm)Pd(II)(R- or S-baetH)], formed a heterometallic tetranuclear complex, [Fe(III){(dbm)Pd(II)(R- or S-baet)}3], in methanol solution.

Synthesis, characterization and biological aspects of novel five-coordinated dimeric-Cu(II) systems

The structural and spectroscopic properties of novel five-coordinated dimeric-Cu(II) system have been investigated. The biocidal activities of all eight compounds, ligands, cupric nitrate and standard drugs against six bacteria and three fungi were determined. The DNA interaction activity of complexes was studied using spectrophotometry and electrophoresis. The superoxide dismutase (SOD)-like activity of the complexes was compared with previously reported monomeric- and dimeric copper complexes. The results support the five-coordinated dimeric square pyramidal geometry for the quinolone-Cu(II) system.

Characterisation of a Mixed N-heterocycle, 2-(N-methylimidazole-2′-yl-thiomethyl)benzimidazole, and its complexes with nickel(II) and copper(II)

2-(N-methylimidazole-2′-yl-thiomethyl)benzimidazole (L) has been synthesised and the complexes [ML2 (ClO4)2]·2H2O (M = Ni or Cu) and [MLX2] nH2O (M = Cu, X = Cl or Br, n = 0; M = Ni, X = Cl, n = 3; M = Ni, X = Br, n = 0) prepared and characterised. Proposed geometries for the complexes are: octahedral geometry for perchlorate complexes; tetrahedral geometry for chloro-and bromo-complexes; dimeric square pyramidal for the chloro-complex of copper(II).

<b>Synthesis and characterization of transition metal complexes derived from some biologically active furoic acid hydrazones</b>

Two new physiologically active ligands, N’-2-[(E)-1-hydroxy-4-methyl-2-oxo-2H-8-chromenyl) ethylidene)-2-furan carbohydrazide (HMCFCH) and N’-2-[(Z)-1-(4-hydroxy-6-methyl-2-oxo-2H-pyranyl) ethylidene]-furan carbohydrazide (HMPFCH) and their VO(II), Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) complexes have been prepared. The ligands and the metal complexes have been characterized by elemental analyses, electrical conductance, magnetic susceptibility measurements, UV-Vis, IR, and ESR spectroscopic data. Basing on the above data, Fe(II) and Co(II) complexes of HMCFCH and HMPFCH have been assigned a dimeric octahedral geometry. VO(II) complexes of HMCFCH and HMPFCH have been assigned sulfate bridged dimeric square pyramidal geometry. Mn(II) complex of HMCFCH has been assigned a dimeric octahedral geometry, where as Mn(II) complex of HMPFCH has been ascribed to monomeric octahedral geometry. Cu(II) and Ni(II) complexes of HMCFCH have been ascribed to a polymeric structure. Ni(II) complex of HMPFCH has been assigned a dimeric square planar geometry. Cu(II) complex of HMPFCH has been proposed an octahedral geometry. The ligands and their metal chelates were screened against S. aureus and P. aeruginosa. The ligands and the metal complexes have been found to be active against these microorganisms. The ligands show more activity than the metal complexes. KEY WORDS: N’-2-(E)-1-hydroxy-4-methyl-2-oxo-2H-8-chromenyl) ethylidene)-2-furan carbohydrazide (HMCFCH), N’-2-[(Z)-1-(4-hydroxy-6-methyl-2-oxo-2H-pyranyl) ethylidene]-furan carbohydrazide (HMPFCH), 3-Acetyl-6-methyl-2H-pyran-2,4(3H)-dione, 8-Acetyl-4-methyl-Umbelliferone, Furoic acid hydrazide, Anti microbial activity Bull. Chem. Soc. Ethiop. 2007, 21(1), 63-73.

Cobalt(II) and copper(II) complexes of (2-thiophene)-(5,6-diphenyl-[1,2,4]-triazin-3-yl)hydrazone

New complexes having the formulae [L2CoX2] and [LCuCl2], [LCuCl] and [LCu](ClO4)2 where L = (2-thiophene)-(5,6-diphenyl-[1,2,4]-triazin-3-yl)hydrazone TDPTH; X = Cl, OAc or ClO4 have been synthesized and characterized on the basis of elemental analyses, conductance, magnetic moments and infrared, electronic and ESR spectral data. The IR spectra indicate that TDPTH is a neutral bidentate ligand, coordinating via a triazine-N and azomethine-N in [L2CoX2] and [LCuCl2] with the thiophene-S not coordinated but is tridentate in [LCuCl] and [LCu](ClO4)2 through the same two nitrogen atoms and thiophene-S. The magnetic moment and electronic spectral data suggest a distorted octahedral structure for Co(II) complexes, a dimeric square pyramidal geometry for [LCuCl2] through chloride bridges and a dimeric diamagnetic, four-coordinate copper in [LCu](ClO4)2 through thiophene-S bridges. The X-band ESR spectra of Co(II) complexes, in the solid state, are rhombic with three g values consistent with a high-spin distorted octahedral structure. The X-band ESR spectrum of the powdered sample of both [LCuCl2]·2H2O and [LCu](ClO4)2 at room temperature and at 77 K showed only one broad signal due to ΔM s = ± 1 transition and a weak signal due to the forbidden ΔM s = ± 2 transition, indicating an antiferromagnetic interaction between copper(II) centers whereas [LCuCl] is ESR silent, indicating a monovalent copper ion in this complex.

Synthesis and characterization of novel nickel(ii) complexes bearing N,P ligands and their catalytic activity in ethylene oligomerization

The novel chloro(1-naphthyl)[8-(diphenylphosphino)quinoline]nickel(II) (1), chloro(1-naphthyl)[2-methyl-8-(diphenylphosphino)quinoline]nickel(II) (2), and [2-methyl-8-(diphenylphosphino)quinoline]nickel(II) dichloride (3) complexes were synthesized in satisfactory yield and fully characterized. The structures of complexes 1 and 3 were determined by single crystal X-ray analysis, which indicated that complex 1 exists in a square planar configuration, while complex 3 is dimeric square pyramidal. In the presence of MAO cocatalyst, complexes 1–3 displayed good catalytic activities for ethylene oligomerization in toluene, up to 2.45 × 105 g ethylene (mol Ni·h·atm)−1 by complex 3.

Cobalt(II, III) and copper(II) complexes of 3-(2-furylidene) hydrazino-5,6-diphenyl-1,2,4-triazine

A new series of cobalt(II, III) and copper(II) complexes of 3-(2-furylidene) hydrazino-5,6-diphenyl-1,2,4-triazine (L) having formulae LMIIX2, L2MIIX2 and LCoIIIX3, (X = Cl, OAc or ClO4; MII = CoII or CuII) were isolated and characterized by elemental analyses, molar conductances, magnetic moments and i.r., electronic and e.s.r. spectral measurements. The i.r. spectra indicated that the ligand, L, behaves as a neutral bidentate towards divalent metal ions via a triazine-N, and azomethine-N, and acts as a tridentate towards cobalt(III) via the same two nitrogen atoms and the furan-O. The magnetic moments and electronic spectral data suggest a pseudo-tetrahedral geometry for [L2Co]Cl2, a diamagnetic tetragonally distorted octahedral geometry for [LCoCl3], [LCo(OAc)3] · 4H2O and [LCo(H2O)3](ClO4)3 and a dimeric square pyramidal geometry for both [LCuCl2] and [LCu(OAc)2] · 2H2O through bridged chloro and acetato ligands, respectively. The ligand field parameters (B′, 10Dq and β) were evaluated from the electronic spectral data and magnetic moments and related to the bonding of the complexes. The X-band e.s.r. spectra showed three g values with large magnetic anisotropy for [L2Co]Cl2 in accordance with pseudo-tetrahedral CoII complexes; axial pattern for [LCuCl2], [LCu(OAc)2] · 2H2O and [L2Cu(H2O)2](ClO4)2 with two g values and a signal due to ΔMs = ±2 transition for both chloro and acetato copper(II) complexes.

Configurational trend in the coordination arrangement of some lanthanide(III) complexes. The crystal and molecular structure of Yb(NCS) 3(THF) 4—II

The series of lanthanide(III) complexes Ln(NCS) 3(THF) 4[Ln = lanthanide(III) ion, THF = tetrahydrofuran] has been synthesized and examined by X-ray diffractometric methods. The study has shown that four oxygen atoms (THF) and three nitrogen atoms (NCS) are arranged around the Ln 3+ ions according to well-defined coordination geometries: the square antiprism (SQA) for eight-coordination and the pentagonal bipyramid (PB) for seven-coordination. The dimeric square antiprismatic structures (Ln = Nd, Gd, Eu, Dy and Er) have been previously described. Here we report the crystal structure of Yb(NCS) 3(THF) 4. The coordination geometry of the metal ion consists of a slightly distorted pentagonal bipyramid, in which two nitrogen atoms (NCS) are in the apical positions and four oxygens atoms (4THF) and one nitrogen (NCS) lie in the equatorial plane. A correlation between the two coordination arrangements (SQA) and (PB) is discussed.

Bivalent metal complexes ofp-methyl- andp-methoxybenzoylhydrazone oximes

Bivalent metal complexes ofp-chloro-,p-methyl- andp-methoxybenzoylhydrazone oximes (H2BMCB, H2BMMB or H2BMTB=H2L), [M(H2L)Cl2]. nH2O (M=ZnII, CdII or HgII, n=0 or 1; [M(H2L)Cl2] (M=ZnII or CdII); [M(HL)2(H2O)n]. YH2O (M=CoII, CuII, ZnII or UVIO2, n=0–2); [Ni(H2BMCB)(H2O)3]Cl2, [Ni(BMMB)(H2O)]2 and [Ni(BMTB)(H2O)]2, were synthesized by conventional physical and chemical measurements. I.r. spectra show that the ligands are bidentate or tridentate. Spectral, magnetic and molecular weight measurements suggest that cobalt(II) and nickel(II) have monomeric octahedral geometry when derived from H2BMCB, a dimeric square planar geometry for nickel(II) and monomeric square planar geometry for cobalt(II) for those isolated from H2BMMB or H2BMTB. Also, a monomeric distorted octahedral structure is proposed for copper(II) complexes derived from the ligands under investigation.

Dimeric square planar complexes of Cu(II) with aroyl hydrazones

Cu(II) complexes with aroyl hydrazones have been prepared in ethanol medium and characterised by elemental analysis. They have 1:1 stoichiometry. I. R. results show that the hydrazones exist in the enol form in the complexes. These Cu(II) complexes show subnormal magnetic moments and the electronic spectra agree with the square planar configuration. In view of the magnetic and electronic spectral evidence, the dimeric square planar configuration is suggested in which CuCu interaction exists.