Bikshandarkoil R. Srinivasan

Thermal and spectroscopic characterization of Mg(II) complexes of nitro-substituted benzoic acids

Abstract The Mg(II) complexes of the nitro-substituted benzoic acids have been investigated by thermal and spectroscopic methods. Thermogravimetry (TG), differential thermal analysis (DTA), differential scanning calorimetry (DSC), and other spectroscopic methods have been used to investigate the thermal behavior and structure of the compounds [Mg(H 2 O) 6 ](4-nba) 2 ·2H 2 O 1 , [Mg(H 2 O) 6 ](3-nba) 2 ·2H 2 O 2 , [Mg(H 2 O) 6 ](2-nba) 2 ·2H 2 O 3 (4-nba= para -nitrobenzoate; 3-nba= meta -nitrobenzoate; and 2-nba= ortho -nitrobenzoate). All the complexes are formulated as consisting of the octahedral [Mg(H 2 O) 6 ] 2+ cation with the carboxylates outside the coordination sphere, which is consistent with the IR, UV-Vis and 1 H NMR data. Thermal decompositions of these carboxylates are multi-stage processes. The composition of the complexes and the solid-state intermediates and the resultant products of thermolysis have been identified by IR, elemental analysis and complexometric titration. A possible scheme for the decomposition of the complexes is suggested. Heating the compounds first results in the loss of water molecules. This is followed by the loss of the nitrobenzoate resulting in the formation of oxide. Complex 1 can be reversibly hydrated. The final product of the thermal decomposition in all the cases is MgO.

Structural, vibrational and thermal studies of a new nonlinear optical material: L-asparagine-L-tartaric acid.

Crystals of a new nonlinear optical (NLO) material, viz., L-asparagine-L-tartaric acid (LALT) (1) were grown by slow evaporation of an aqueous solution containing equimolar concentrations of L-asparagine and L-tartaric acid. The structure of the title compound which crystallizes in the non-centrosymmetric monoclinic space group P2(1) consists of a molecule of L-asparagine and a molecule of free l-tartaric acid both of which are interlinked by three varieties of H-bonding interactions namely O-H···O, N-H···O and C-H···O. The UV-Vis-NIR spectrum of 1 reveals its transparent nature while the vibrational spectra confirm the presence of the functional groups in 1. The thermal stability and second harmonic generation (SHG) conversion efficiency of 1 were investigated.

On the existence of ‘l-alanine cadmium bromide’

It is argued that the recently reported nonlinear optical crystal L-alanine cadmium bromide, grown by slow solvent evaporation method at room temperature [P. Ilayabarathi, J. Chandrasekaran, Spectrochim. Acta 96A (2012) 684-689] is the well-known L-alanine crystal. The isolation of L-alanine crystal is explained due to fractional crystallization.

Synthesis and characterization of a new strontium(II) coordination polymer based on a μ2-tridentate bridging zwitterionic glycine

The synthesis and characterization of a new Sr(II) coordination polymer (CP), [Sr(H2O)(H-gly)2Cl2] n (1) (H-gly = glycine), is described. Compound 1 crystallizes in the centrosymmetric orthorhombic space group Pcnb and its structure consists of a central Sr(II), a water molecule, a zwitterionic glycine, and a chloride. The central metal is nine coordinate, bonded to six oxygens from four different bridging H-gly ligands, two symmetry-related chlorides, and a terminal water molecule. The μ2-tridentate bridging zwitterionic glycine results in the formation of a 1-D CP with an Sr···Sr separation of 4.560 Å across the chain. The chloride, H-gly, and coordinated water are involved in five varieties of hydrogen bonding. A comparative study of the structural chemistry of several alkaline-earth glycine compounds is described.

Reinvestigation of growth of urea thiosemicarbazone monohydrate crystal.

The reaction of urea with thiosemicarbazide in 1:1 mole ratio in aqueous solution does not result in the formation of urea thiosemicarbazone monohydrate crystal, as reported by Hanumantharao, Kalainathan and Bhagavannarayana [Spectrochim. Acta A91 (2012) 345-351]. A reinvestigation of the reported reaction reveals that the crystal obtained is the starting material namely thiosemicarbazide, which has been unambiguously confirmed with the aid of infrared and (1)H NMR spectra and single crystal X-ray structure determination. Analysis of (1)H NMR spectrum reveals that thiosemicarbazide exhibits thione-thiol tautomerism in solution. In contrast, thiosemicarbazide exists as the thione tautomer in the solid state.

Can zinc(II) ions be doped into the crystal structure of L-proline cadmium chloride monohydrate?

The bivalent metals Cd(II) and Zn(II) exhibit different stereochemical requirements for the set of chloride and L-proline ligands, which precludes the doping of Zn(II) ions into the crystal structure of dichloro(l-proline)cadmium(II) hydrate also referred to as L-proline cadmium chloride monohydrate (L-PCCM). Hence, the reported claim of growth of zinc doped L-PCCM crystals namely Zn(0.4 mol):LPCCM and Zn(0.2 mol):LPCCM by Vetrivel et al. (S. Vetrivel, P. Anandan, K. Kanagasabapathy, S. Bhattacharya, S. Gopinath, R. Rajasekaran, Effect of zinc chloride on the growth and characterization of l-proline cadmium chloride monohydrate semiorganic NLO single crystals, Spectrochim. Acta 110A (2013) 317-323), is untenable.

Does an all-sulphur analogue of heptamolybdate exist?

The complexes [MoX4]2− (M = Mo; X = O or S) exist as the monomeric tetrahedral species in aqueous alkaline solutions. Acidification of tetraoxomolybdate results in the condensation of the tetrahedral units via a series of polyoxomolybdates leading to the ultimate formation of the trioxide MoO3. Heptamolybdate [Mo7O24]6− is the first major polyanion of the acidification reaction. In contrast, acidification of tetrathiomolybdates leads to the formation of amorphous molybdenum trisulphide via a dinuclear Mo(V) complex. The formation of the dinuclear Mo(V) complex precludes the formation of any higher nuclearity Mo(VI)-S complexes in aqueous solution. Thus it is shown that the all-sulphur analogue of heptamolybdate [M07S24]6− does not exist in alkaline medium and also cannot be isolated from aqueous acidic medium

Reinvestigation of growth of 'L-valine zinc sulphate' crystal.

A reinvestigation of the growth of l-valine zinc sulphate crystal is reported. The slow evaporation of an aqueous solution containing l-valine and zinc sulphate heptahydrate results in the fractional crystallization of l-valine and not the organic inorganic hybrid nonlinear optical l-valine zinc sulphate crystal, as reported by Puhal Raj and Ramachandra Raja (2012).

A calcium(II) coordination polymer showing two different bridging 2-carbamoyl-4-nitrobenzoate coordination modes

Aqueous reaction of CaCO3 with 2-carbamoyl-4-nitrobenzoic acid (2-ca-4nbaH) results in the formation of a 1-D coordination polymer [Ca(H2O)2(2-ca-4nba)2] (1), which crystallizes in the centrosymmetric triclinic space group P 1. The structure consists of a central Ca(II), two coordinated waters, a symmetrical bridging (µ2-η 1 : η 1) 2-ca-4nba, and a tridentate bridging (µ2-η 2 : η 1) 2-ca-4nba. The calcium in 1 is coordinated by two water molecules and five oxygens of four symmetry-related 2-ca-4nba, resulting in a distorted pentagonal bipyramidal {CaO7} polyhedron. Pairs of {Ca(H2O)2} units are linked into a 1-D coordination polymer extending along the a-axis with the aid of pairs of bridging 2-ca-4nba ligands. In the infinite chain, alternating pairs of Ca(II) ions exhibit Ca ··· Ca separations of 4.124 and 4.855 Å.

1,3-Propanediammonium tetrathiotungstate and N,N,N',N'-tetramethylethylenediammonium tetrathiotungstate

The title complexes, (C(3)H(12)N(2))[WS(4)] and (C(6)H(18)N(2))[WS(4)], contain tetrahedral [WS(4)](2-) dianions, which accept a complex series of hydrogen bonds from the organic dications. The strength and number of these hydrogen bonds affect the W-S distances.