One-dimensional cadmium(II)/bicinate(−1) complexes : The role of the alkali metal ion used in the reaction medium

The initial employment of N,N-bis(2-hydroxyethyl)glycine (bicine; bicH₃) in CdCl₂ chemistry is reported, and the syntheses, IR spectra and crystal structures of the 1D coordination polymers [CdCl(bicH₂)]_n·nH₂O (1·H₂O) and [CdNaCl₂(bicH₂)(MeOH)]_n (2) are described. The identity of the products depends on the solvent, the reaction temperature and the alkali metal ion of the base used. The structure of 1·H₂O consists of zig-zag chains. The 7-coordinate Cd^II atoms are bridged by η¹:η¹:μ₂ carboxylate groups of the 2.21111 (Harris notation) bicH₂⁻ ligand. The coordination geometry of the metal center can be either described as a very distorted pentagonal bipyramidal or as a distorted capped octahedral. In the structure of 2 the Cd^II atoms form an almost linear chain with neighboring Na^I atoms on opposite sites of the chain. Every pair of Cd^II atoms is linked by two chloro ligands and the two oxygen atoms of the bicinate carboxylate group. The Cd^II and Na^I atoms are bridged by one μ₂ carboxylate bicinate oxygen and one μ₃ chloro ligand. The 3.2_1,21₁1₂1₂1₂ coordination mode of bicH₂⁻ is unprecedented. The CdCl₄(O_carboxylate)₂ and Na(O_hydroxyl)₂(O_carboxylate)(O_MeOH)NCl coordination spheres are octahedral and trigonal prismatic, respectively. IR data of the complexes are discussed in terms of the coordination modes of bicH₂⁻ and the known structures.