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

Abstract

AbstractFollowing 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.