Manas Kumar Saha

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 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.

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.

Synthesis, characterization and crystal structure of cyano-bridged dinuclear copper–iron complexes

Abstract Two new cyano-bridged dinuclear complexes [Cu(dmen)2Fe(CN)5(NO)] (1) and [Cu(dmpn)2Fe(CN)5(NO)] (2) (where dmen=2-dimethylaminoethylamine and dmpn=1 dimethylamino-2-propylamine) have been synthesized. The complexes have been characterized by elemental analyses, spectroscopic studies and magnetic moment measurements, and the structures were determined using single-crystal X-ray diffraction. In both complexes the copper(II) ion is coordinated by five nitrogen atoms and has distorted square-pyramidal geometry. The iron(II) center is in a distorted octahedral environment and is linked to copper(II) through a cyano-bridge.

Synthesis and crystal structure of mononuclear copper (II) complex of tridentate Schiff base ligand and its ferrocyanide-bridged pentanuclear complex

Abstract The compound [Cu(L)(OAc)H2O] (1) (HL is a tridentate Schiff base derived from 2-hydroxyacetophenone and 2-dimethylaminoethylamine) has been synthesized and its crystal structure has been determined. The addition of [Fe(CN)6]4− to [Cu(L)(OAc)H2O] gives the pentanuclear complex [(CuL)4Fe(CN)6]·16H2O (2). Four Cu(II) centres are joined to a single Fe(II) centre via cyanide bridges. The two remaining cyanide groups on the iron are terminal. The presence of sixteen water molecules per pentanuclear complex has been confirmed by thermogravimetric analysis and the activation energy for the elimination of water has been computed and found to be 57 kJ mol−1.

Structural and magnetic properties of a syn-anti carboxylate bridged one-dimensional copper(II) complex with ferromagnetic exchange interaction

The compound [Cu(phen)(O2CCF3)2]n (phen = 1,10-phenanthroline) has been synthesized and its crystal structure determined. It crystallizes in monoclinic space group C2/c, with a = 19.229(7), b = 11.281(5), c = 7.621(2) Å, β = 104.305(12)°, and Z = 4. The crystal structure is polymeric, being built from infinite zigzag chains of trifluoroacetate bridged copper(II), with the phenanthroline ligands being stacked between the chains. The variable-temperature (13–300 K) magnetic susceptibility and ESR data are reported and a weak ferromagnetic exchange interaction is observed with the exchange parameter estimated as J = 2.9 cm−1.

SYNTHESIS AND STRUCTURE OF A HEPTACOORDINATED CADMIUM(II) COMPLEX

Abstract A heptacoordinated Cd(II) complex bis(1,10-phenanthroline)bis(trifluoroacetato)cadmium(II) has been synthesised; its structure is distorted pentagonal bipyramidal. 113Cd NMR spectroscopy has been done to correlate the structure. The compound is characterised by a single resonance at 111 ppm deshielded from 0.1 M Cd(ClO4)2 · 6H2O.

Synthesis, characterisation, reactivity and X-ray crystal structure of a mixed-ligand η1-salicylaldehyde complex of Mn (III)

Abstract A tridentate ligand L has been synthesised from salicylaldehyde and 1-dimethylamino-2-propylamine. It undergoes partial hydrolysis to regenerate salicylaldehyde in methanolic KOH solution. Reaction of manganese (II) acetate with this solution, followed by addition of sodium thiocyanate, produces a dark brown complex [Mn (L) (NCS){o- (CHO)C6H4O}] (1), which has been crystallographically characterised. Coordination of Mn is Jahn–Teller distorted octahedral by L, salicylaldehyde, and thiocyanate. The coordinated aldehyde group reacts with 2-aminoethanol and with 2-aminophenol to give mononuclear neutral Mn (III) complexes 2 and 3, respectively, with mixed Schiff-base ligands, [Mn (L) (L′)]. Complexes 1 and 2 are high-spin, while 3 is low-spin.

THERMALLY INDUCED ELECTRON-TRANSFER REACTIONS OF HETEROMETALLIC DINUCLEAR COMPLEXES IN THE SOLID STATE

Thermally induced electron-transfer reactions of dinuclear complexes of the composition [L2MnII(H2O)2][L2MnII(CN)2FeIII(CN)4]2·6H2O, where L = 1,10-phenanthroline 1 or 2,2′-bipyridyl 2, have been carried out. Both the complexes have been synthesized and characterized by elemental analysis, IR, electronic, EPR, Mossbauer spectra and thermal analysis. Heating in an inert atmosphere at 210°C for complex 1 and at 190°C for complex 2 caused conversion to [MnII(Phen)2(H2O)2][(Phen)2MnIII(CN)2 FeII(CN)4]2 la and [MnII(bipy)2(H2O)2][(bipy)2MnII(CN)2FeII(CN)4]2 2a with a sharp colour change from yellow to reddish brown in each case. Thermal investigation of complexes 1 and 2 under non-isothermal conditions in a dynamic inert atmosphere showed endothermic peaks in DTA curves at 210 and 190°C, respectively, whereas no mass loss in the corresponding TGA curves was observed. The rate constant of the electron transfer has been evaluated from DTA curves at different temperatures. Activation energy and enthalpy change were also evaluated. This process is irreversible as no peak appeared in the DTA curve on cooling. X-ray powder diffraction patterns were recorded and showed that 1, la and 2, 2a are almost identical. We were not able to synthesize single crystals of the complexes 1 and 1a, 2 and 2a due to the lack of solubility in most of the solvents.

Synthesis, characterisation and crystal structure of a 1,4-diazacycloheptane complex of copper(II)

Abstract A new complex of formula [Cu(dach) 2 (CCl 3 CO 2 )]CCl 3 CO 2 (dach=1,4-diazacycloheptane) has been synthesised and its crystal structure determined by single-crystal X-ray diffraction. The crystal structure contains two independent copper(II)-centred cations (one disordered) and two trichloroacetate ions. Both copper(II) atoms are pentacoordinate. The chelated 1,4-diazacycloheptane moieties are in a double boat conformation and represent the first structurally characterised example of a trans configuration for two such ligands at a metal centre. The compound was also characterised by IR, electronic and EPR spectra, cyclic voltammetry, and magnetic susceptibility studies.