Samiran Mitra

Synthesis and structural characterization of mixed ligand η1-2-hydroxyacetophenone complexes of cobalt(III)

Abstract A tridentate Schiff base ligand [(CH3)2NCH2CH2NC(CH3)C6H4OH)] (LH) has been synthesized from 2-hydroxyacetophenone and 2-dimethylaminoethylamine. This ligand forms the neutral complexes [Co(L)(N3){o-(CH3CO)C6H4O}] (1) and [Co(L)(SCN){o-(CH3CO)C6H4O}]·1/2H2O (2) in presence of equivalent amount of Co(II) acetate, and sodium azide for 1 and sodium thiocyanate for 2. The complexes have been characterized by spectroscopic and crystallographic methods. The coordination geometry around Co(III) in both the complexes is distorted octahedral with one tridentate ligand L, one bidentate 2-hydroxyacetophenone and one monodentate azide for 1 and thiocyanate for 2. The azide and thiocyanate ligands in the two complexes occupy different positions relative to the coordination sites of L.

Synthesis, characterization and structural studies of mono- and polynuclear complexes of zinc(II) with 1,10-phenanthroline, 2,2′-bipyridine and 4,4′-bipyridine

Abstract Three complexes of the formula [Zn(2,2′-biny)(CCl3CO2)2(H2O)] (1). [Zn (1,10-phen) (CCl3CO2)2(H2O)] (1a) and [Zn(μ-4,4′-bipy)(4-4′-bipy)2(CCl3CO2)2(H2O)4]n (2) have been synthesized and characterized by elemental analysis, IR spectra, thermal analysis and single-crystal X-ray diffraction for 1 and 2 and X-ray powder pattern for 1a. The metal coordination in complex 1 is distorted trigonal bipyramidal with N(1), O(2) and O(5) defining the basal plane, O(3) and N(2) being in apical positions. The X-ray crystal structure of 2 reveals that the local coordination round the ZnII ion is a distorted octahedron, in which Zn(H2O)4 coordination planes are bridged by 4,4′-bipyridine to form an infinite chain structure. Two 4,4′-bipyridine molecules and two trichloroacetate anions exist in the lattice linked by intermolecular hydrogen bonds to coordinated water molecule. Complexes 1 and 1a have a similar pattern of bonding and showed identical TGA curve and almost similar X-ray powder diffractograms.

Synthesis, characterization and crystal structures of some four coordinated nickel(II) complexes with tridentate Schiff base ligands

Abstract A number of Ni(II) complexes with tridentate Schiff base ligands with a N2O donor set and coordinating NNN− and SCN− anions have been synthesized and characterized by analytical, spectroscopic and electrochemical techniques. X-ray structure analyses of three of these complexes [L1Ni(NNN)] (1), [L2Ni(NNN)] (2) and [L3Ni(NCS)] (6) [HL1=Me2NCH2CH2N(Me)C6H4OH, HL2=Et2NCH2CH2N(H)C6H4OH, HL3=Et2NCH2CH2N(H)C6H3BrOH] show that the nickel atom has a square planar geometry. Thermogravimetric studies show multiple step decomposition, and electrochemical studies indicate that the complexes are irreversibly oxidized to Ni(III) species, which are unstable and undergo rapid decomposition.

Synthesis and characterization of diorganotin(IV) complexes of tetradentate Schiff bases: Crystal structure of n-Bu2Sn(Vanophen)

Abstract Diorganotin(IV) complexes of the general formula R2SnL (R=Ph, n-Bu and Me) have been prepared from diorganotin(IV) dichlorides (R2SnCl2) and tetradentate Schiff bases (H2L) containing N2O2 donor atoms in the presence of triethylamine in benzene. The Schiff bases, H2L, were derived from salicylaldehyde, 3-methoxysalicylaldehyde (o-vanillin), 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone and diamines such as o-phenylenediamine and 1,3-propylenediamine. The complexes were characterized by IR, NMR (1H, 13C, 119Sn) and elemental analysis. The structure of the complex, n-Bu2Sn(Vanophen), was determined using single crystal X-ray diffraction. The tin atom has a distorted octahedral coordination, with the Vanophen ligand occupying the four equatorial positions and the n-butyl groups in the trans axial positions. Six-coordinated distorted octahedral structures have been proposed for all diorganotin(IV) complexes studied here, as they possess similar spectroscopic data.

Isolation of four new CoII/CoIII and NiII complexes with a pentadentate Schiff base ligand: syntheses, structural descriptions and magnetic studies

In this paper we report the temperature and pH dependent syntheses and systematic characterization of four new Co(II)/Co(III) and Ni(II) complexes with a pentadentate Schiff base ligand H(3)L obtained by condensing 1,3,-diaminopropan-2-ol with 2-hydroxyacetophenone in 1:2 molar ratio. The room temperature syntheses involving Co(II) and Ni(II) nitrates and the ligand H(3)L lead to the isolation of the dinuclear species [Co(2)L(2)(H(2)O)] (1), and the mononuclear complex [Ni(LH)] (3), respectively, whereas refluxing at basic pH leads to the tetranuclear complexes, [Co(II)(2)Co(III)(2)L(2)(μ(3)-OMe)(2)(NO(3))(H(2)O)(2)]NO(3)·2(H(2)O) (2), and [Ni(4)L(2)(μ(3)-OMe)(2)(H(2)O)(2)]·2H(2)O (4). 1 is found to be a simple mono alkoxo-bridged Co(III) dinuclear species, whereas 2 and 4 are both rhomb-like tetrameric complexes with double oxo bridges and μ(3)-methoxo bridges, derived from the methanol solvent, in an open dicubane arrangement. Moreover 2 shows six coordinate ordered Co(II) and Co(III) ions and 4 has both six- and five-coordinate Ni(II) centers. Compound 3 is assigned a tentative mononuclear structure based on IR, UV-Vis spectroscopic, (1)H-NMR and ESI mass study results and is supposed to have one Ni(II) center coordinated with a ligand fragment in square planar geometry. The variable temperature magnetic susceptibility study for 2 and 4 is performed which indicate for both 2 and 4 the presence of intracluster dominant ferromagnetic interactions.

Weak Interactions Modulating the Dimensionality in Supramolecular Architectures in Three New Nickel(II)-Hydrazone Complexes, Magnetostructural Correlation, and Catalytic Potential for Epoxidation of Alkenes under Phase Transfer Conditions

Three different ONO donor acetyl hydrazone Schiff bases have been synthesized from the condensation of acetic hydrazide with three different carbonyl compounds: salicylaldehyde (HL(1)), 2-hydroxyacetophenone (HL(2)), and 2, 3-dihydroxybenzaldehyde (HL(3)). These tridentate ligands are reacted with Ni(OOCCF(3))(2)·xH(2)O to yield three new Ni(II) complexes having distorted octahedral geometry at each Ni center: [Ni(L(1))(OOCCF(3))(CH(3)OH)](2) (1), [Ni(L(2))(OOCCF(3))(H(2)O)](2) (2), and [Ni(L(3))(L(3)H)](OOCCF(3))(H(2)O)(1.65)(CH(3)OH)(0.35) (3). The ligands and the complexes have been characterized by elemental analysis and IR and UV-vis spectroscopy, and the structures of the complexes have been established by single crystal X-ray diffraction (XRD) study. 1 and 2 are centrosymmetric dinuclear complexes and are structural isomers whereas 3 is a bis chelated cationic monomer coordinated by one neutral and one monoanionic ligand. O-H···O hydrogen bonds in 3 lead to the formation of a dimer. Slight steric and electronic modifications in the ligand backbone provoke differences in the supramolecular architectures of the complexes, leading to a variety of one, two, and three-dimensional hydrogen bonded networks in complexes 1-3 respectively. Variable temperature magnetic susceptibility measurements reveal that moderate antiferromagnetic interactions operate between phenoxo bridged Ni(II) dimers in 1 and 2 whereas very weak antiferromagnetic exchange occurs through hydrogen bonding and π-π stacking interactions in 3. All complexes are proved to be efficient catalysts for the epoxidation of alkenes by NaOCl under phase transfer condition. The efficiency of alkene epoxidation is dramatically enhanced by lowering the pH, and the reactions are supposed to involve high valent Ni(III)-OCl or Ni(III)-O· intermediates. 3 is the best epoxidation catalyst among the three complexes with 99% conversion and very high turnover number (TON, 396).

Synthesis, characterisation and structural studies of [Cu(dach)(μ-NCS)(NCS)]n and [Cu(dach)2(N3)]ClO4 (dach = 1,4-diazacycloheptane)

Abstract A new singly bridging complex [Cu(dach)(μ-NCS)(NCS)] n (dach=1,4-diazacycloheptane) has been synthesised and its crystal structure determined. There are many examples of double NCS bridged polymeric chains, but fewer singly bridged ones. IR, ESR and temperature variable magnetic studies are described but no magnetic interaction was found between the copper centres. [Cu(dach) 2 (N 3 )]ClO 4 has also been characterised by IR, ESR spectra and magnetic studies. The crystal structure determination shows that it is a penta-coordinated monomeric species with an axially coordinated azide linked to the perchlorate counterion by hydrogen bonding.

Syntheses, characterisation, magnetism and photoluminescence of a homodinuclear Ln(III)-Schiff base family

A novel family of homodinuclear complexes of the general formula [Ln(2)L(2)(X)(2)] (where Ln = Nd(3+), Pr(3+), Sm(3+) and Tb(3+) for 1, 2, 3 and 4, respectively and X, the coordinated NO(3)(-) or Cl(-) anion) has been synthesised from the corresponding lanthanide(III) salts with the pentadentate dianionic Schiff base ligand, H(2)L [N(1),N(3)-bis(salicylideneimino)diethylenetriamine], that exhibits a N(3)O(2) donor set. Single crystal X-ray diffraction studies evidenced the isostructurality of this family of centrosymmetric neutral dinuclear entities where the Ln(III) metal centres are coupled together by two phenolato oxygen atoms belonging to two units of ligand (H(2)L). Interestingly, the two other phenolato groups of H(2)L are mono-coordinated to the metal ions. Temperature dependence (2-300K) magnetic susceptibility studies suggest the presence of an antiferromagnetic interaction operating via double phenolato bridges. Photoluminescence activities of the complexes have been studied and compared with their precursor ligand. All the complexes have been characterised with microanalytical and several spectroscopic techniques.

Synthesis, spectroscopy and structure of [N-(2-carboxyphenyl)salicylideneiminato]dimethyltin(IV)

Abstract The novel dimethyltin complex with formula Me 2 Sn(2-OC 6 H 4 CHNC 6 H 4 COO), compound 1 , involving the Schiff base derived from anthranilic acid and salicylaldehyde, has been synthesized and characterized by elemental analysis, IR, 1 H-, 13 C- and 117 Sn-NMR, 119 Sn Mossbauer spectroscopy and single-crystal X-ray diffraction structure analysis. The crystals of complex 1 are monoclinic, space group P 2 1 / n , a =8.907(5), b =12.044(7), c =14.062(9) A, β =104.99(5)°, Z =4, R 1 =0.0296, wR 2 =0.08 for 1368 observed reflections. The crystal structure of 1 features centrosymmetric dimers disposed about a central Sn 2 O 2 core. The tin environment is seven-coordinate if a moderately long contact distance Sn(1)O(2a) (2.69(1) A) and a longer one Sn(1)O(3a) (3.03(1) A) are included in the coordination list. In the basic monomeric structural unit, the tin configuration can be seen as a distorted square-pyramid with the imine nitrogen atom in apical position, the N -(2-carboxyphenyl)salicylideneimine dianion coordinating a single tin atom via the phenolate oxygen atom, the imine nitrogen atom and one of the carboxylate oxygen atoms. The distortion of the square pyramid is discussed in terms of a trend to trigonal-bipyramidal geometry.

First report of singly phenoxo-bridged copper(II) dimeric complexes: synthesis, crystal structure and low-temperature magnetic behaviour study

Three singly phenoxo-bridged dinuclear Cu(II) complexes [Cu2(L)2(SCN)(H2O)](ClO4) 1, [Cu2(L)2(N3)(H2O)](ClO4) 2, [Cu2(L)2(NCO)(H2O)](ClO4) 3 (HL is the Schiff base ligand derived from O-vanillin and 2-aminomethyl ethylenediamine) have been synthesised and characterised by infrared, UV-Vis spectra, electrochemical study and single crystal X-ray diffraction study. In all the complexes (1–3), there are two geometrically different square pyramidal copper(II) centres, with N3O2 and N2O3 donor sets for the two Cu(II) centres. In the dimeric unit, the copper atoms are held together by only one distinct rare μ2-phenolate oxygen of one Schiff base. The Cu–Cu distances are 3.291(2), 3.244(1) and 3.244(1) A for complexes 1, 2 and 3, respectively, and the Cu–O–Cu angles are found to be 111.5(1), 109.3(2), 109.6(1)° for complexes 1, 2 and 3, respectively. Variable temperature magnetic susceptibility study on the complexes 1,2 and 3 indicate the presence of antiferromagnetic coupling between the Cu(II) centres with 2J values −109.8, −103.9 and −95.9 cm−1, respectively.