Metal aminocarboxylate coordination polymers with chain and layered structures

Abstract

The synthesis and structures of metal aminocarboxylates prepared in acidic, neutral, or alkaline media have been explored with the purpose of isolating coordination polymers with linear chain and two-dimensional layered structures. Metal glycinates of the formulae [CoCl₂(H₂O)₂(CO₂CH₂NH₃)] (I), [MnCl₂(CO₂CH₂NH₃)₂] (II), and [Cd₃Cl₆(CO₂CH₂NH₃)₄] (III) with one-dimensional chain structures have been obtained by the reaction of the metal salts with glycine in an acidic medium under hydro/solvothermal conditions. These chain compounds contain glycine in the zwitterionic form. 4-Aminobutyric acid transforms to a cyclic amide under such reaction conditions, and the amide forms a chain compound of the formula [CdBr₂(C₄H₇NO)₂] (IV). Glycine in the zwitterionic form also forms a two-dimensional layered compound of the formula [Mn(H₂O)₂(CO₂CH₂NH₃)₂]Br₂ (V). 6-Aminocaproic acid under alkaline conditions forms layered compounds with metals at room temperature, the metal being coordinated both by the amino nitrogen and the carboxyl oxygen atoms. Of the two layered compounds [Cd{CO₂(CH₂)₅NH₂}₂]·2H₂O (VI) and [Cu{CO₂(CH₂)₅NH₂}2]·2H₂O (VII), the latter has voids in which water molecules reside.