Polymethylene spacer regulated structural divergence in cadmium complexes: Unusual trigonal prismatic and severely distorted octahedral coordination

Chelation of the tetradentate pyridyl di-Schiff-base ligands, N, N'-bi s-(1-pyridin-2-yl-ethylidene)-propane-1,3-diamine (L-1) or N,N'-bis-(1-pyridin-2-yl-ethylidene)-ethane-1,2-diamine (L-2) to a cadmium(II) centre reveals interesting structural deviations from regular octahedral geometry in the resulting hexacoordinated complexes [Cd(L-1)(NCS)(2)] (1) and [Cd(L-2)(NCS)(2)] (2), respectively. The two tetradentate lilgands L-1 and L-2 differ only in the polymethylene chain - (CH2)(3) and (CH2)(2), respectively, which connects the two halves of the symmetric ligands. Complex I assumes a trigonal prismatic (TP) geometry. The structure of 2 reveals a severely distorted octahedral geometry. The structural differences between [Cd(L-1)(NCS)(2)] (1) and [Cd(L-2)(NCS)(2)] (2) can be traced to the length of the polymethylene spacers and the formation of a six- versus a five-membered metal-chelate ring together with the pyramidal Cd(L-1) and planar Cd(L-2) arrangement. (c) 2005 Elsevier Ltd. All rights reserved.