Syntheses, characterisation and solid state thermal studies of 1-(2-aminoethyl)piperidine (L), 1-(2-aminoethyl)pyrrolidine (L ') and 4-(2-aminoethyl)morpholine (L '') complexes of nickel(II): X-ray single crystal structure analyses of trans-[NiL2(CH3CN)(2)](ClO4)(2), trans-[NiL2(NCS)(2)] and trans-[NiL2 ''(NCS)(2)]

Reactions of nickel(II) salts with substituted ethane-1,2-diamine where one of the amine nitrogens is a part of a flexible cyclic ring, e.g. 1-(2-amin oethyl)piperidine (L), 1-(2-aminoethyl)pyrrolidine (L') and 4-(2-aminoethyl )morpholine (L") produce a number of complexes of the type: (i) Ni(A-A)(2)X -2 (where X=CF3CO2- SCN- and NO2- A-A represents L/L'/L"); (ii) Ni(A-A)(2)( CH3CN)(2)X-2 (X=ClO4- and NO3-); (iii) Ni(A-A)(2)(H2O)(2)X-2 (X=CF3SO3- Cl- , Br- and I-); and (iv) Ni(A-A)(2)(H2O)(4)X-2 (X = 0.5SO(4)(2-), 0.5SeO(4)( 2-) and CF3SO3-). The complexes possess octahedral geometry. The major comp lexes upon desolvation retain trans-geometry, some of which are cis with re spect to the counter-anion and a few of them are square planar. X-ray singl e crystal structure analyses of trans-[NiL2(CH3CN)(2)](ClO4)(2), trans-[NiL 2(NCS)(2)] (violet) and trans-[NiL2"(NCS)(2)] (sky-blue) have been done. Th e violet and sky-blue thiocyanato species have blue and green coloured isom ers, respectively, and these pairs of isomers are proposed to be conformati onal isomers. Solid state thermal investigation of the complexes has been c arried out. The complexes show thermochromism due to deaquation-anation/dea quation reaction/change of conformation. Only [NiL2](ClO4)(2), [NiL2'(CF3CO 2)(2)] and [NiL2"(NO2)(2)] undergo thermally induced phase transition. The effect of flexible ring size on diamine has been discussed. (C) 2001 Elsevi er Science Ltd. All rights reserved.