Crystal structure and magnetic behavior of Cu3(O2C16H23)6·1.2 C6H12. An unexpected structure and an example of spin frustration

Abstract

A copper(II) carboxylate has been obtained from the reaction of basic copper carbonate, CuCO₃·Cu(OH)₂, with 2,4,6-triisopropylbenzoic acid. It contains a trinuclear Cu₃⁶⁺ core with three-fold symmetry, with each pair of copper atoms bridged by two carboxylate ligands. The Cu···Cu separations are 3.131(3) Å, precluding any direct bonding. Magnetic susceptibility data from 1.8 to 380 K at 1 000 G indicate a doublet ground state, (g ≈ 2.1) between 10–50 K (μ_eff = 1.80 μ_B). Above 50 K, the magnetic moment increases to 2.69 μ_B at 380 K, as expected for an equilateral triangular system of Cu^II with antiferromagnetic interactions between spin carriers.