Bonding Capabilities of the Biochemical Buffer TRIS toward Copper(II) Ion. Structure and Magnetic Properties of Binuclear and Tetranuclear Systems

Following X-ray crystal structure studies, the products of the reaction between Cu(II) halides and tris(hydroxymethyl)methylamine (TRIS) can be formulated as [Cu(TRISH_?1)(TRIS)]₂X₂ and [Cu(TRISH_?1)X]₄ (X ? Cl, Br). TRISH_?1 is the deprotonated ligand. Initial metal-ligand stoichiometric ratios of 1:2 and 1:1 are required to obtain the former and the latter species, respectively. Relevant crystal data for the dimeric compound with X ? Br are: monoclinic, a = 11.39(2), b = 10.049(2), c = 12.149(2) Å, β = 95.83(2)°, space group P2₁/c, Z = 2. The tetramer with X ? Cl crystallizes in teh triclinic space group P 1 with a 9.182(1), b = 9.120(2), c = 8.817(1) Å, α = 88.95(1), β = 87.01(1), γ = 84.13(1), Z = 1. In the dimer, two square planar Cu(II)-units are held together by two H-bonds of the type O? H …? O, which involve the O-atoms coordinated to the metals. The formation of an eight-membered cycle containing two metal ons ensues. The tetramer contains two dinuclear units formed by two metal centers, square planar in first approximation, which share one edge; the arrangement is significantly puckered at this vector. One of these bridging O-atoms has μ₃ character as it serves as a weak apical donor for a Cu-atom of another binuclear unit. Thus a step-like geometry of the central core is obtained. Both compounds have constant magnetic moments at least down to the liquid N₂ temperature. In this respect, they differ from other complexes of Cu(II) having comparable geometries, but temperature-dependent magnetic moments.