Dimeric Geometry 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.

Synthesis, Characterization, and Catalytic Activity of Bimetallic Ti/Cr Complexes

We report herein the reactions of the Rosenthal complexes, Cp2Ti(BTMSA) and Cp*2Ti(BTMSA) (BTMSA: bis(trimethylsilyl)acetylene), with CpCr(CO)3H. Those complexes are known to dissociate their alkyne ligands and to exhibit the reactivities of the putative titanocenes “Cp2Ti” and “Cp*2Ti”. Our reactions appear to proceed through the addition of CpCr(CO)3H to these titanocenes, giving rise to TiIV-H intermediates that lose H2 to form the TiIII–Cr complexes 1 and 2. In the solid state, 1 and 2 both adopt a dimeric geometry, involving a 12-membered “Ti2Cr2” ring held together with Ti–O–C–Cr bridging carbonyls. The terminal carbonyls in 1 and 2 are trans. DFT calculations confirm that the loss of H2 from the TiIV-H intermediate—forming the TiIII-Cr dimer—is exergonic by 14.2 kcal mol–1 in the gas phase. The Bercaw compound Cp* (C5Me4CH2)TiCH3 reacts with CpCr(CO)3H to form a TiIV-CH3 species with a coordinated CpCr(CO)3– anion (3). The Ti-Cr dimer 1 is capable of catalyzing the hydrogenation of an epoxide to an anti-Markovnikov alcohol, avoiding the use of Cp2TiX2 (X = Cl– or mesylate), NaCpCr(CO)3, and HCpCr(CO)3 separately as in our previous catalyst system.

Functional insights into the mode of DNA and ligand binding of the TetR family regulator TylP from Streptomyces fradiae

Tetracycline repressors (TetRs) modulate multidrug efflux pathways in several pathogenic bacteria. In Streptomyces, they additionally regulate secondary metabolic pathways like antibiotic production. For instance, in the antibiotic producer Streptomyces fradiae, a layered network of TetRs regulates the levels of the commercially important antibiotic tylosin, with TylP occupying the top of this cascading network. TetRs exist in two functional states, the DNA-bound and the ligand-bound form, which are allosterically regulated. Here, to develop deeper insights into the factors that govern allostery, the crystal structure of TylP was solved to a resolution of 2.3 Å. The structure revealed that TylP possesses several unique features; notably, it harbors a unique C-terminal helix-loop extension that spans the entire length of the structure. This anchor connects the DNA-binding domain (DBD) with the ligand-binding domain (LBD) via a mix of positively charged and hydrogen-bonding interactions. Supporting EMSA studies with a series of ΔC truncated versions show that a systematic deletion of this region results in complete loss of DNA binding. The structure additionally revealed that TylP is markedly different in the orientation of its DBD and LBD architecture and the dimeric geometry from its hypothesized Streptomyces homologue CprB, which is a γ-butyrolactone regulator. Rather, TylP is closer in structural design to macrolide-binding TetRs found in pathogens. Supporting molecular dynamic studies suggested that TylP binds a macrolide intermediate in the tylosin pathway. Collectively, the structure along with corroborating biochemical studies provided insights into the novel mode of regulation of TetRs in antibiotic-producing organisms.

Reaction of thiosemicarbazide with some divalent ions: Synthesis, characterization, molecular modeling, and evaluation of the catalytic and biological activity of the complexes

ABSTRACTNew metal complexes of Co(II) and Cu(I) have been synthetized by reaction of metal salts with thiosemicarbazide (TSC: HL1) and urea (U). The metal complexes were characterized on the basis of elemental analyses, molar conductance, spectral (IR, 1H NMR) studies, as well as thermogravimetric analysis. The spectral data show that in the complexes, only TSC is coordinated to the metal. The IR spectra of Co(II) and Cu(I) complexes are different. In addition to the bands of TSC, a new intense band at 2100 cm−1 is assigned to the thiocyanate fragment produced in situ by the cleavage of the TSC C–N bond. On the basis of spectral studies, a N3O3 high-spin environment was assigned to [Co(II)(L1)(SCN)(H2O)3] complex and a dimeric form geometry for Cu(I) complex of general formula [Cu(I)(HL1)(SCN)(H2O)]. In order to gain a better insight into the molecular structure and the reactivity of the ligand and its complexes, quantum chemical calculations were also performed to determine some electronic properties and geometric parameters of the ligand and Cu(I) and Co(II) complexes. The metal complexes have been tested for catalase-like activity in order to assess their catalytic properties. The results seem encouraging. The biological activity of the ligand and its metal complexes is evaluated as well.

Binuclear Tetrahedral Dimeric Mg(II) Complexes of DibasicTridentate Schiff Base Ligands and Their Microbial Studies

Some Mg(II) complexes of dibasic tridentate Schiff base ligands derived from aldehydes and orthoaminophenol have been synthesized and characterized by some physico-chemical studies; elemental, spectral (IR, UV, NMR), magnetic and conductance analyses. Dimeric tetrahedral geometry for the prepared com- plexes has been proposed. The antibacterial activity of the prepared complexes was also studied against some gram positive and gram negative bacteria.

Crystal Structure of a Human IκB Kinase β Asymmetric Dimer

Phosphorylation of inhibitor of nuclear transcription factor κB (IκB) by IκB kinase (IKK) triggers the degradation of IκB and migration of cytoplasmic κB to the nucleus where it promotes the transcription of its target genes. Activation of IKK is achieved by phosphorylation of its main subunit, IKKβ, at the activation loop sites. Here, we report the 2.8 Å resolution crystal structure of human IKKβ (hIKKβ), which is partially phosphorylated and bound to the staurosporine analog K252a. The hIKKβ protomer adopts a trimodular structure that closely resembles that from Xenopus laevis (xIKKβ): an N-terminal kinase domain (KD), a central ubiquitin-like domain (ULD), and a C-terminal scaffold/dimerization domain (SDD). Although hIKKβ and xIKKβ utilize a similar dimerization mode, their overall geometries are distinct. In contrast to the structure resembling closed shears reported previously for xIKKβ, hIKKβ exists as an open asymmetric dimer in which the two KDs are further apart, with one in an active and the other in an inactive conformation. Dimer interactions are limited to the C-terminal six-helix bundle that acts as a hinge between the two subunits. The observed domain movements in the structures of IKKβ may represent trans-phosphorylation steps that accompany IKKβ activation.

Synthesis and crystal structure determination of Mn(II) Schiff base complexes and their performance in ethene polymerization

Mn(II) complexes 1–10, of which eight are novel, were prepared in high yields by reacting MnCl2 with bidentate N,N′-imine-pyridine and N,N′-imine-quinoline-type donor ligands having different kinds of chemical modifications. The complexes were fully characterized by elemental analysis, mass spectrometry and IR spectroscopy. Crystal structures of 6, 7 and 9 were determined by X-ray crystallography and the results showed that 6 has a dimeric square-pyramidal geometry, whereas 7 and 9 have distorted octahedral structures. Magnetic studies on the high spin complexes 6 and 9 showed that the former exhibits a weak intramolecular antiferromagnetic interaction through the chloride-bridging ligands with a magnetic exchange coupling J=−0.46(6) cm−1, whereas the latter, as expected for its mononuclear structure, only shows very weak intermolecular interactions and/or zero-field splitting effects. All the complexes were activated with methylaluminoxane and investigated under low pressure (5bar) for ethene polymerization at 60°C. Complexes 1 and 6–10 showed catalytic activity. The prepared polyethenes exhibited high molar masses (296000–399000g/mol) and high melting temperatures (133–140°C). The low molar mass distribution values of 2.15–2.55 indicated single-site polymerization behavior.

Cation and ligand roles in the coordination of FeIII bisdithiolene complexes; the crystal structures of (BrBzPy)2[Fe(qdt)2]2 and [Fe(α-tpdt)2]22− salts

The crystal structure of the new (BrBzPy)2[Fe(qdt)2]2 complex (qdt = quinoxalinedithiolate) shows a rare weak FeIII bisdithiolene dimerisation with unusual molecular planarity and long apical S–Fe distances. This anion configuration is intermediate between the only monomeric Fe bisdithiolene reported so far, with isolated square planar [Fe(qdt)2]− units, and the common strong dimeric geometry also observed in other [Fe(qdt)2]2 salts. The standard strong dimeric situation is also observed in the [Fe(α-tpdt)2]2 salt (α-tpdt = 2,3-thiophenedithiolate) with the same cation, as well as with n-Bu4N and Et4N showing the influence of different ligands and cations on the coordination geometry and supramolecular structure of the FeIII complexes.

<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.

Preparation and physico-chemical characterisation of iron(III) complexes containing substituted benzimidazole and Schiff base moieties

New complexes of iron(III) of the type [(μ-Cl)2Fe2{η 2-(opbz)4] (1) and [(Cl)2Fe{η 2-(opbz)] (2) [Hopbz = {2-(o-hydroxyphenyl)}-benzimidazole, η 2 = Number of connectivity sites involved in bonding the metal] have been synthesized by the interactions of iron(III) chloride with the corresponding ligand (Hopbz) in 1:2 and 1:1 molar ratio(s) in hot EtOH. The complex (1) was further treated with various sodium salts of Schiff bases (sb) [Na(o-smab), Na(p-smab) and Na(sap)], alkoxo-Na(OPri), aryloxo-Na(OAr) and tetraisopropoxyaluminate [Na{Al(OPri)4] in a 1:1 molar ratio (in THF–benzene medium) to produce derivatives of the type: {(η 2-(sb) Fe{η 2-opbz)2] (3), (4) and (5), [(μ-OPri)2Fe2{η-(opbz)4}] (6) [(μ-OAr)2Fe2{η-(opbz)4}] (7) and [(μ-OPri)2Al(OPri)2-Fe{η-(opbz)2}] (8). All these derivatives were characterised by elemental analysis, spectral (IR, UV–visible and FAB-mass) and magnetic susceptibility measurements. On the basis of these studies, a distorted octahedral (dimeric) geometry around iron(III) for the complexes (1), (6), (7) and (8) have been suggested.

Crystal structures of [Rh(η 5-C 5H 5)(C 3S 5)] and [Rh(η 5-C 5Me 5)(C 3S 5)] 2 and properties of their oxidized species

[Rh(η 5-C 5H 5)(C 3S 5)] and [Rh(η 5-C 5Me 5)(C 3S 5)] 2 [C 3S 5 2−=4,5-disulfanyl-1,3-dithiole-2-thionate(2-)] were prepared by reactions of [NMe 4] 2[C 3S 5] with [Rh(η 5-C 5H 5)Cl 2] 2 and [Rh(η 5-C 5Me 5)Cl 2] 2, respectively. Their X-ray crystal structural analyses revealed a monomeric form for the former complex and a dimeric geometry containing bridging S–Rh–S bonds for the latter in the solid state. They were reacted with bromine to afford [RhBr(L)(C 3S 5)] (L=η 5-C 5H 5 and η 5-C 5Me 5) with the Rh–Br bond and one electron-oxidation on the C 3S 5 ligand. ESR spectra and spin densities for these oxidized species are discussed.

New Electrophilic Iridium(I) Complexes: H−H and C−H Bond Heterolysis by [(dfepe)Ir(μ-X)]2(X = O2CCF3, OTf)

New electrophilic dimeric iridium(I) complexes [(dfepe)Ir(μ-X)]2 (dfepe = (C2F5)2PCH2CH2P(C2F5)2; X = O2CCF3, OTf) have been prepared and their reactions with H2 and cyclopentane examined. Treatment of [(cod)Ir(O2CCF3)]2 with dfepe produced an ionic product [(dfepe)Ir(cod)]+[(dfepe)Ir(O2CCF3)2]- (1), which in refluxing benzene rearranged with loss of cyclooctadiene to form [(dfepe)Ir(μ-O2CCF3)]2 (2). The corresponding reaction of [(cod)Rh(O2CCF3)]2 with dfepe yielded [(dfepe)Rh(μ-O2CCF3)]2 (3) directly. X-ray diffraction analysis of 2 revealed a hinged dimeric geometry with an unusually large interplanar angle of 82.7° defined by the two 4-coordinate metal centers (Ir(1)−Ir(2) = 4.307 A). The triflate-bridged analogue of 2 was prepared via an indirect route: addition of 1 equiv of triflic acid to (dfepe)Ir(η3-C3H5) yielded the allyl hydride complex (dfepe)Ir(η3-C3H5)(H)(OTf) (4), which eliminated propylene in refluxing heptane to quantitatively afford [(dfepe)Ir(μ-O3SCF3)]2 (5). The structure of 4 was co...

Synthesis, characterization and biological activities of some new nickel(II), copper(II), zinc(II) and cadmium(II) complexes of quadridentate SNNS ligands

The quadridentate ligands, prepared by condensation ofS-methyl- andS-benzyldithiocarbazate with glyoxal, form stable crystalline complexes of gerferal formula, M(SNNS) (M=NiII, CuII, ZnII and CdII; SNNS−2=ligand dianion). The NiII complexes are diamagnetic but electronic spectral data support a dimeric five-coordinate geometry. Based on magnetic and spectral data, a five-coordinate square-pyramidal structure is also assigned to the copper(II) complexes. The ZnII and CdII complexes are polymeric and octahedral. The Schiff bases and metal complexes display good antifungal and antibacterial properties.

Synthesis and X-ray crystal structure of the hexafluoroantimonate salt of the dimeric tungsten pentacarbonyl diselenyl cation W2(CO)10Se42+

Reaction of W(CO)6 with Se4(Sb2F11)2 in SO2 results in the formation of a compound formulated as W2(CO)10Se42+(SbF6–)2 the dimeric cation geometry of which has been established by X-ray crystal structure determination.

The (metal-metal)-nonbonding[Fe2(CO)6(.mu.2-PPh2)2]2- dianion. Synthesis, structural analysis of its unusual dimeric geometry, and stereochemical-bonding implications

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe (metal-metal)-nonbonding[Fe2(CO)6(.mu.2-PPh2)2]2- dianion. Synthesis, structural analysis of its unusual dimeric geometry, and stereochemical-bonding implicationsRobert E. Ginsburg, Richard K. Rothrock, Richard G. Finke, James P. Collman, and Lawrence F. DahlCite this: J. Am. Chem. Soc. 1979, 101, 22, 6550–6562Publication Date (Print):October 1, 1979Publication History Published online1 May 2002Published inissue 1 October 1979https://doi.org/10.1021/ja00516a013RIGHTS & PERMISSIONSArticle Views182Altmetric-Citations61LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Coordination compounds of hydrazine derivatives with transition metals—VII: Metal(II) complexes with hydrazine s-methyl dithiocarboxylate Schiff bases and their pyridine adducts

Metal(II) chelates of general formula M( R 1 R 2CN−NCSSCH 3) 2 ( MNi( II), Co(II) and Cu(II); R 1 = R 2 = CH 3; R 1, R 2 = C 5H 10 − and R 1 = CH 3, R 2 = C 6H 5) were prepared and investigated. Magnetic and spectral data indicated square planar Ni(II) complexes while Co(II) afforded tetrahedral complexes. All the Cu(II) chelates probably possessed a dimeric pentacoordinate geometry. The reaction of pyridine with the bis metal (II) complexes were discussed. Monopyridinate adducts were isolated with the bis (N-isopropylidene hydrazine-S-methyldithiocarboxylate) cobalt (II) and nickel (II) chelates.