On the interaction of copper with tris(hydroxymethyl)aminomethane

Abstract

The interaction of copper with tris(hydroxymethyl)aminomethane (TRIS) has been studied by optical and esr spectroscopic techniques. In solution, three different copper complexes are obtained as a function of pH. At pH 10 the room temperature esr parameters are g0 = 2.135, A0 = 82 G and nitrogen superhyperfine structure /tN = 9.5 G, characteristic of two nitrogen ligands; at pH 6.5, go = 2.147, A0 = 65 G and at pH 5.0, g0 = 2.180, A0 = 44 G. The high pH complex was crystallized and its molecular structure determined by X-ray methods. Space group and cell dimensions are C2/c, a = 12.955(2) Å, b = 10.793(1) Å, c= 10.091(2) Å,β= 116.62(1)°, V= 1261.4(6)Å3 = 4, Dc = 1.694gcm-3, R = 0.034 for 938 reflections with I > 3σ(I). The Cu2+ ion is located on the two-fold axis and coordinated to the oxygen and nitrogen atoms of two TRIS moieties; these ligand atoms form the rectangular base of a pyramid structure in which oxygen from a water molecule acts as the fifth ligand.