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 CuII/H-Aib-l-Ala-OH (LH) reaction system is described, where H-Aib-l-Ala-OH is α-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 η1:η1:η1:μ2 ligand binding one CuII atom through its amino nitrogen and neutral peptide oxygen, and an adjacent CuII 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.