Synthesis of conformational isomers, thermally induced isomerism, and crystal structure of cis-di-isothiocyanatobis(N-methylpropane-1,3-diamine)nickel(II)
Two isomers, (1) and (1a), of [NiL2(NCS)2](L =N-methylpropane-1,3-diamine) have been synthesised. Isomer (1) undergoes an irreversible endothermic solid-state phase transition (383–413 K, ΔH= 8.1 kJ mol–1) transforming into species (1a). This isomerisation also takes place on crystallisation from methanol, ethanol, chloroform, or acetonitrile. Species (1a) has been characterised by X-ray crystallography. The crystals are monoclinic, space group P21/c with four formula units in a unit cell of dimensions a= 8.136(2), b= 13.057(2), c= 15.235(3)Å, and β= 90.75(1)°. The structure has been solved by Patterson and successive Fourier syntheses and refined by block-diagonal least-squares calculations to R= 0.048 and R′= 0.061 for 2 311 reflections. The metal atom co-ordination is nearly octahedral with the two thiocyanate groups in cis position. The overall configuration and conformation of the complex molecule is Λpp(two chairs fold in the same rotational direction). Isomer (1) probably exists in the Λpa form (two chairs fold apart from each other).