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Two tetranuclear and two mononuclear Cu(II) complexes with arylhydrazones of malononitrile derived ligands (compounds 1–2 and 3–4, respectively), one trinuclear Co(II/III) complex with an arylhydrazone of acetoacetanilide (5) and one tetranuclear Zn(II) complex of 3-(2-carboxyphenyl-hydrazone)pentane-2,4-dione (6) were screened as potential catalysts in the peroxidative oxidation of cyclohexane by aqueous H2O2 in acetonitrile. The best results were attained in the presence of pyrazine-2-carboxylic acid (PCA) with 1 (26% yield, TON = 52.0) and with 2 (24%, TON = 48.0) after 4 h at 40 °C. In the presence of complexes 5 and 6, no oxygenated products were detected in the studied conditions. The employment of non-conventional conditions like supercritical carbon dioxide (scCO2) as reaction medium or microwave (MW) irradiation was assessed for complexes 1 and 2. After 6 h in acetonitrile–scCO2, at 50 °C and with HNO3 as promoter, only 17% yield was achieved using 1 as catalyst, and 21% using 2. Total yields of oxygenates up to 14 (with 1) and 13% (2) and TOFs of 56.0 and 52.0 h−1, respectively, were obtained working under MW irradiation at 70 °C and for the much shorter time of 0.5 h. [ABSTRACT FROM AUTHOR]

Complexes based on nitrogen and sulfur containing ligands involving 3d metal centers are known for the electrocatalytic reduction of CO2. However, photocatalytical activation has rarely been investigated. We herein present results on the light-driven CO2 reduction using either Ir(dFppy)3 [Ir, dFppy = 2-(4,6-difluorophenyl)pyridine] or [Cu(xant)(bcp)]+, (Cu, xant = xantphos, bcp = bathocuproine) as photosensitizer in combination with TEA (triethylamine) as sacrificial electron donor. The 3d metal catalysts have either dptacn (dipicolyl-triazacyclononane, LN3) or dpdatcn (dipicolyl-diazathiocyclononane, LN2S) as ligand framework and Fe3+, Co3+ or Ni2+ as central metal ion. It turned out that the choice of ligand, metal center and solvent composition influences the selectivity for product formation, which means that the gaseous reduction products can be solely CO or H2 or a mixture of both. The ratio between these two products can be controlled by the right choice of reaction conditions. With using Cu as photosensitizer, we could introduce an intermolecular system that is based solely on 3d metal compounds being able to reduce CO2.

• Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes of 1,2-benzothiazine based ligand. • Hirshfeld surface analysis for the copper complex. • DFT studies of 1,2-benzothiazine derived Cu(II) complex. • Antibacterial studies of metal complexes was carried out. The 2-benzyl-4‑hydroxy-1,1-dioxo-1,2-benzothiazine-3-carboxylic acid methyl ester i.e., ligand 1 was utilized to synthesize Mn(II) 2 , Co(II) 3 , Ni(II) 4 , Cu(II) 5 and Zn(II) 6 derived metal complexes in mild basic conditions. The structural investigation was carried out by UV–vis, FT-IR, NMR spectroscopy, CHN analysis, conductivity measurement, ESI-MS analysis and magnetic susceptibility techniques. The X-ray diffraction analysis confirmed the octahedral and distorted square pyramidal geometries of the cobalt and copper complexes. The ligand 1 coordinated with metal centres through enolic oxygen atoms of the thiazine ring and ester group while methanol coordinated with metal center via oxygen atom. The Hirshfeld surface analysis (HSA) was utilized to determine the intermolecular interactions. In support of the experimental data, DFT studies were also performed for the cobalt and copper complexes. The NBO analysis resulted in the large stabilization values 11.91 and 12.35 kcal/mol for the cobalt and copper complexes. The global reactivity indicated the higher values of hardness and the large values of FMO analysis which support the higher stability of the metal complexes. The synthesized compounds were also evaluated against six bacterial strains to check their antibacterial potential. It was observed from results that highest activity was depicted by copper complex 5 against B. subtilis and the zone of inhibition is 23.4 ± 0.6 mm which is comparable to ampicillin (standard drug). [ABSTRACT FROM AUTHOR]

The tridentate, monoanionic bis(oxazolinylmethylidene)‐isoindolate pincer ligand was utilized for the synthesis of various cobalt(II) high‐spin complexes. Employing standard complexation procedures, the corresponding acetato and chlorido complexes were isolated in good yields and thoroughly characterized in the solid‐state and in solution. In particular, a density functional theory (DFT) supported paramagnetic NMR analysis revealed a strong correlation between observed 13C NMR shifts and calculated spin‐density distributions, allowing for an unambiguous signal assignment in all 1H and 13C NMR spectra. An acetato‐bridged trinuclear cobalt species as well as the hexacoordinate "homoleptic" complex [(Rboxmi)2Co] were further identified as side products generated in the complex synthesis. The chlorido complexes were applied as catalysts for the cobalt‐catalyzed hydrosilylation of acetophenone, producing the chiral secondary alcohol with moderate enantioselectivities. [ABSTRACT FROM AUTHOR]

The new 3d metal complexes of pyrimidine-2-carboxylic (2PCA) and pyrimidine-5-carboxylic (5PCA) acids were synthesized and characterized using thermal analysis (TG–DSC, TG–FTIR), X-ray, spectroscopic (IR, Raman) methods and theoretical (DFT) studies. In the complexes of pyrimidine-2-carboxylic acid of the general formula M(2PCA)2·xH2O (where 2PCA-pyrimidine-2-carboxylate; M = Mn(II), Co(II), Ni(II), Cu(II) and Zn; x = 0 for Mn and Cu; x = 2 for Co, Ni and Zn) coordination of metal ions occurs through nitrogen atom from pyrimidine ring and carboxylate oxygen atom. The complexes of pyrimidine-5-carboxylic acid of the general formula M(5PCA)2·xH2O (where 5PCA—pyrimidine-5-carboxylate; M = Mn(II), Co(II), Ni(II), Cu(II) and Zn; x = 6 for Cu and 4 for remaining complexes) were obtained as monomeric isostructural compounds. Coordination of metal centers occurs through two nitrogen atom from different pyrimidine-5-carboxylate ligand and four oxygen atoms from water molecules. The IR and Raman spectra of free acids as well as obtained metal(II) complexes were described in detail. Aromaticity (HOMA, EN, GEO and I6) of complexes was determined and discussed. The investigated compounds decompose in air in two main stages connected with dehydration and decomposition/burning of anhydrous compounds to the suitable metal oxides. Thermal decomposition in nitrogen leads to the evolution of water, carbon oxides, ammonia and pyrimidine molecules. [ABSTRACT FROM AUTHOR]

Novel Cu(II), Fe(III), Co(III) and Ni(II) coordination compounds with a 2-[(2-hydroxyphenyl)methylene]hydrazine-N-(2-propenyl)carbothioamide have been synthesized and characterized by single crystal X-ray diffraction, IR, UV–Vis, 1 H, ( 13 C) NMR and X-ray photoelectron spectroscopy. The optimal conditions for the complexation reactions have been determined. Depending on synthesis conditions the ligand coordinates to the metal ion as a neutral molecule, monoanion or bianion mode forming complexes with composition [Cu(H 2 L)Cl] ( I ), [Fe(H 2 L) 2 ]NO 3 ( II ), [Co(H 2 L) 2 ]Cl ( III ) and [Ni(HL)Py] ( IV ). The stability constants for the compounds I − III have been calculated. It has been found that the ligand molecules are coordinated in a tridentate manner by the sulfur, azomethine nitrogen and phenol oxygen in both thione (complexes I − III ) or thiolic (complex IV ) tautomeric forms. [ABSTRACT FROM AUTHOR]

The crystal structure of tetra(μ-acetato)-bis{[1-ethyl-3-(pyridine-2-yl)carbamide]copper} Cu 2(L) 2(CH 3COO) 4 ( I), where L is 1-ethyl-3-(pyridine-2-yl)carbamide, is determined. The asymmetric unit cell of the crystal structure of I contains a copper complex with two acetate ions and a monodentate molecule of 1-ethyl-3-(pyridine-2-yl)carbamide, which is coordinated via the pyridine nitrogen atom. Due to the symmetry center, binuclear complexes form in the crystal, in which the acetate ions act as bridges between the metal atoms. In them, the coordination polyhedron of the central copper atoms represents an almost ideal tetragonal pyramid. Its base is formed from the oxygen atoms of acetate ions. In the crystal of the binuclear complex, hydrogen bonds form between the acetate ions and the L ligand along with an intramolecular hydrogen bond, which stabilize the conformation of the organic L molecule. Between the neighboring complexes in the crystal, the van der Waals interaction occurs. [ABSTRACT FROM AUTHOR]

Abstract: The present article summarizes the results of our studies of 3d metal complexes with various Schiff bases. Structural features, regularities of changes of the (M–N) and (M–O) bond lengths, as well as their correlation with electronic structure of the metal atom are discussed. [Copyright &y& Elsevier]

reaction of acetylacetone with the framework sandwich-type metallosiloxanes (MOS) of general formula [PhSiO]M[PhSiO], where M = Cu, Ni, Mn, was studied by GPC, H and Si NMR spectroscopy, X-ray diffraction, elemental and functional analysis. The reaction involved replacement of the metal atoms with the hydrogen atoms and is accompanied by the formation of the corresponding chelate complexes M(acac). Displacement of the metal from the framework MOS leads to the destruction of molecular skeleton and formation of phenylsiloxanes containing Si-OH groups. The yield and composition of the reaction products considerably depend on the nature of the metal in [PhSiO]M[ThSiO]. A selective substitution of the metal leads to the stereoregular hexahydroxyhexaphenylcyclohexasiloxane, [PhSiO(PH)], cis-isomer. The structure and composition of the crystalline hexahydroxyhexaphenylcyclohexasiloxane obtained were confirmed by Si NMR spectroscopy, X-ray diffraction study, and functional analysis, while its TMS derivative was studied with H NMR spectroscopy and GPC. Using a framework manganese phenylsiloxane as an example, a reversible character of the process has been established and an alternative synthesis of this compound from hexahydroxyhexaphenylcyclohexasiloxane and Mn(acac) has been accomplished for the first time. [ABSTRACT FROM AUTHOR]

Abstract: Mono-nuclear complexes [M(CPI)6](X)2 (M=Co, X=NO3 − 1; M=Ni, X=NO3 − 2; M=Cu, X=ClO4 − 3) and [Cu(CPI)4(H2O)2](NO3)2 4, based on novel bridging ligand 1-(4-cyanophenyl)-imidazole (CPI) are reported. The complexes have been characterized by elemental analyses, spectral studies and their molecular structures have been authenticated by single crystal X-ray diffraction analyses. In molecular species 1–3 metal centers are coordinated octahedrally by six CPI ligands wherein cyanophenyl rings of six ligands about the complex cations are involved in face-to-face π–π interaction with six co-planar molecules to afford unprecedented 2D sheet. Along ‘c’-axis it gives a beautiful rim like motif. In complex 4, coordination about metal center Cu is distorted octahedral with four CPI ligands in the equatorial position and two water molecules occupying axial positions. In this complex hydrogen bonding interactions between the coordinated water molecules and nitrate anions results in a 1D straight chain along ‘a’-axis and 2D sheets having hexagonal cavity filled by nitrate ions. The complexes upon excitation at 275–285nm exhibit luminescences with emission maxima centered at 438–445nm attributable to the ligand CPI at room temperature. [Copyright &y& Elsevier]

Abstract: The chemistry of first row transition metal complexes obtained from the ligand dipyrido[3,2-f:2′,3′-h]-quinoxaline (dpq) have been reported. The reaction between Cu(ClO4)2 ·6H2O with dpq under different reaction conditions led to the isolation of three polymorphic copper(II) complexes [Cu(dpq)2(H2O)](ClO4)2 ·H2O (2), [Cu(dpq)2(ClO4)](ClO4) (3) and [{Cu(dpq)2(H2O)}{Cu(dpq)2(ClO4)}](ClO4)3 (4). The bluish-green compound 2, obtained by reacting Cu(ClO4)2 ·6H2O with dpq in methanol, has a distorted trigonal bipyramidal structure with τ =0.55. The reaction between Cu(ClO4)2 ·6H2O and dpq in dry acetonitrile produced the blue compound 3 in which the copper(II) centre has a distorted square planar geometry. When the condensation reaction between 1,10-phenanthroline-5,6-dione and 1,2-diaminoethane was carried out in the presence of Cu(ClO4)2 ·6H2O in methanol, the green copper(II) complex 4 was isolated along with 1. The structure determination of 4 has established the presence of two different complex cations in the asymmetric unit and they are considered as co-crystals. In the zinc(II) compound [Zn(dpq)2(ClO4)2] (5), the two perchlorates are unidentately coordinated to the metal centre, providing a distorted octahedral geometry. The quinoxaline ring in 5 is involved in intermolecular π–π interactions, leading to the generation of a sinusoidal chain. The proton NMR spectra, especially those of the paramagnetic complexes [Ni(dpq)3](ClO4)2 (6) and [Co(dpq)3](ClO4)2 (7), have been studied in detail. The electronic absorption spectra and the redox behaviour of the copper(I), copper(II), cobalt(II) and cobalt(III) complexes have been studied. The three copper(II) compounds 2–4 show identical absorption spectra and redox properties when measured in acetonitrile, although in nitromethane they show small but definite differences in their spectral and redox features. [Copyright &y& Elsevier]

Hydrazones derived from substituted benzoyl hydrazides and benzil a-monoxime [viz. benzil a-monoxime benzoylhydrazone (BMBH), benzil a-monoxime 4-chlorobenzoylhydrazone (BMPCBH), benzil a-monoxime 4-methoxybenzoylhydrazone (BMMBH), benzil a-monoxime 4-nitrobenzoylhydrazone (BMNBH) and benzil a-monoxime 2-chlorobenzoylhydrazone (BMOCBH)] have been synthesized and used in preparing the corresponding Cr(III), Mn(III), Fe(III) and Co(III) complexes. The ligands undergo deprotonation in ethanolic alkaline solution to form dinuclear complexes. The complexes are insoluble in common organic solvents, decompose above 300°C, and are spin-free octahedral. The complexes isolated were characterized by elemental analyses, IR, electronic, 1 H NMR spectra, conductance, thermal studies and magnetic susceptibility measurements. The bonding and probable structures of the complexes are discussed on the basis of the spectral and magnetic data. The ligands, as well as their complexes, show antifungal activity. [ABSTRACT FROM AUTHOR]

A novel mesogenic Schiff base, N-(4-butylphenyl) salicylaldimine (Hbpsal), was prepared and its ligational behavior towards some 3 d metal ions studied. All the metal complexes synthesized were of the general formula, [M(bpsal) 2 (H 2 O) 2 ] where M=Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). The complexes were structurally characterized by elemental analyses, molar conductance, IR, NMR, and electronic spectral data. The metallo mesogenic phases of the Cu(II) complex were studied by optical microscope. The spectral data show that Hbpsal acts as a bidentate ligand towards the metal ions. Mesogenic studies indicate that the ligand shows a focalconic structure with smectic-A phase while the Cu(II) complex displays smectic-A as well as smectic-E phases. [ABSTRACT FROM AUTHOR]

The complexes[M(L)(H2O)x]n[M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II)] and[M2(L)3]n[M = Mn(III), Fe(III)] and[VO(HL)2] with N-picolinoyl-N′-2-furanthiocarbohydrazide(H2L) have been prepared and characterized by elemental analyses, magnetic susceptibility measurement, electronic, NMR(1H and 13C), IR and FAB mass spectral data. Physico-chemical studies indicate that the complexes are polymeric in nature. The room temperature ESR spectra of[VO(HL)2] and[Cu(L)]n complexes yield〈g〉 values, characteristic of square-pyramidal and square-planar complexes, respectively. The Mössbauer spectra of[Fe2(L)3]n at room temperature and at 78 K suggest the presence of high-spin(S = 5/2) and low-spin(S = 1/2) forms of Fe(III) in the same complex at both temperatures. The complexes of OV(IV), Fe(III), Ni(II), and Cd(II) show semiconducting behaviour in the solid state in the temperature range 307–397 K, with a band gap of 0.18–0.44 eV. The other complexes are insulators. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydration of alkynes with low cost first row transition metals. • Water addition to alkynes catalyzed by iron, cobalt, nickel, copper or zinc complexes. • Cobalt catalysts in reductive hydration of alkynes to chiral alcohols. • Environmental friendly nucleophilic additions to unsaturated C–C triple bond. • Regioselective hydration of internal alkynes under combined acid catalysis. The review describes the state of the art in hydration reactions of alkynes by direct or indirect catalysis of first row transition metal complexes, covering mostly the literature of the last decade in which many examples based on these metal ions have been reported. Previously limited to few cases, catalytic metal ions of the fourth period allow for the regioselective conversion of terminal and internal alkynes with different electronic properties or even sterically hindered into the corresponding ketones. The substrate scope includes aromatic, heteroaromatic and aliphatic alkynes under reaction conditions compatible with various functional groups, in moderately acidic conditions, as for iron catalysts, or even in absence of Brønsted acids, as for cobalt and copper salts. The mechanism of activation of the triple bond varies largely depending on the metal ion and includes attack of proton under combined acid catalysis (Lewis acid-Brønsted acid) or intermediacy of π-alkyne or σ-acetylide late transition metal-complexes. The use of 3d metal complexes as alternatives to conventional noble metal catalysts for water addition reactions of alkynes entails significant implications on cost and environmental issues. Selected examples of applications in cascade and multi step reactions involving acid sensitive organic compounds are also described. [ABSTRACT FROM AUTHOR]

Dacarbazine (DAC) 5-(3,3-dimethyl-1-triazenyl)imidazole-4-carboxamide is an imidazole-carboxamide derivative that is structurally related to purines. DAC belongs to the triazene compounds, which are a group of alkylating agents with antitumor and mutagenic properties. DAC is a non-cell cycle specific drug, active in all phases of the cellular cycle. In the frame of this work the 3d metal complexes (cobalt and copper) with dacarbazine were synthesized. Their spectroscopic properties by the use of FT-IR, FT-Raman, and 1HNMR were studied. The structures of dacarbazine and its complexes with copper(II) and cobalt(II) were calculated using DFT methods. The effect of metals on the electronic charge distribution of dacarbazine was discussed on the basis of calculated NBO atomic charges. The reactivity of metal complexes in relation to ligand alone was estimated on the basis of calculated energy of HOMO and LUMO orbitals. The aromaticity of the imidazole ring in dacarbazine and the complexes were compared (on the basis of calculated geometric indices of aromaticity). Thermal stability of the investigated 3d-metal complexes with dacarbazine and the products of their thermal decomposition were analyzed. [ABSTRACT FROM AUTHOR]