The dipeptide H-Aib-L-Ala-OH ligand in copper(II) chemistry: Variation of product identity as a function of pH

A systematic investigation of the influence of pH on the product identity from the Cu-II(H-Aib-L-Ala-OH (LH) reaction system is described, where H-Aib-L-Ala-OH is alpha-aminoisobutyryl-L-alanine. The pH variation has led to the synthesis of two discrete complexes, the structures of which have been determined by single-crystal X-ray crystallography. The low pH complex {[CuClL](H2O)2.5}(n) (1) is a 3D coordination polymer, in which the dipeptide monoanion L- behaves as a eta(1) :eta(1) :eta(1) :mu(2) ligand binding one Cu-II atom through its amino nitrogen and neutral peptide oxygen, and an adjacent Cull atom through one of its carboxylate oxygen. The higher pH complex {[Cu(H-1L)(EtOH)](EtOH)}(n) (2) is a chain (1D) compound, in which the dipeptide dianion H-1L2- uses its amino nitrogen, deprotonated peptide nitrogen and both carboxylate oxygens to bridge two metal centres. (c) 2005 Elsevier B.V. All rights reserved.