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)
摘要:
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-ray single crystal structures of [Ni(pren)(2)(CF3CO2)(2)] 3 and [Ni(pren)(2)(CF3CO2)(2)] 4 are determined. Both 3 and 4 have slightly distorted 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(eten)(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 conformational changes in diamine chelate rings. (C) 1998 Elsevier Science Ltd. All rights reserved.