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

Abstract

Chelation of the tetradentate pyridyl di-Schiff-base ligands, N,N′-bis-(1-pyridin-2-yl-ethylidene)-propane-1,3-diamine (L¹) or N,N′-bis-(1-pyridin-2-yl-ethylidene)-ethane-1,2-diamine (L²) to a cadmium (II) centre reveals interesting structural deviations from regular octahedral geometry in the resulting hexacoordinated complexes [Cd(L¹)(NCS)₂] (1) and [Cd(L²)(NCS)₂] (2), respectively. The two tetradentate ligands L¹ and L² differ only in the polymethylene chain – (CH₂)₃ and (CH₂)₂, respectively, which connects the two halves of the symmetric ligands. Complex 1 assumes a Trigonal Prismatic (TP) geometry. The structure of 2 reveals a severely distorted octahedral geometry. The structural differences between [Cd(L¹)(NCS)₂] (1) and [Cd(L²)(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(L¹) and planar Cd(L²) arrangement.