SYNTHESES AND CHARACTERIZATION OF DIAMINE COMPLEXES OF NICKEL(II) TRIFLUOROACETATE - THERMOCHROMISM AND X-RAY SINGLE-CRYSTAL STRUCTURE ANALYSES OF [NI(PREN)(2)(CF3CO2)(2)] AND [NI(IPREN)(2)(CF3CO2)(2)] (PREN =N-PROPYLETHANE-1,2-DIAMINE AND IPREN= N-ISOPROPYLETHANE-1,2-DIAMINE)

The complexes, [NiL2(CF3CO2)(2)] [L = N-methylethane-1,2-diamine (meen ), N-ethylethane-1,2-diamine (eten), N-propylethane-1,2-diamine (pren) and N-isopropylethane-1,2-diamine (ipren)] have been prepared and X-r ay single crystal structures of [Ni(pren)(2)(CF3CO2)(2)] 3 and [Ni(pre n)(2)(CF3CO2)(2)] 4 are determined. Both 3 and 4 have slightly distort ed trans-octahedral geometry with N4O2-chromophore around nickel(II). The crystals are stabilized by H-bonds and this interaction is higher in 4 due to close proximity of methyl H-atoms of isopropyl group with oxygen atoms of trifluoroacetate groups. The complexes 3 and 4 exhibit blue to light-violet. irreversible discontinuous thermochromism. [Ni( meen)(2)(CF3CO2)(2)] 1 also shows thermochromism, blue-violet to blue bur reverts on keeping in humid atmosphere. On the other hand, [Ni(ete n)(2)(CF3CO2)(2)] 2 undergoes decomposition without showing any phase transition. However, thermochromism here is considered to be due to a decreased in-plane ligand field strength resulting from the conformati onal changes in diamine chelate rings. (C) 1998 Elsevier Science Ltd. All rights reserved.