AbstractA new hexanuclear copper(II) sandwich complex based on two 12‐membered macrocyclic methylsiloxanolate ligands, [Cu6{(MeSiO2)6}2]·6DMF, was synthesized and characterized by single‐crystal X‐ray diffraction analysis and magnetic measurements. The cluster compound crystallizes in the monoclinic system, space group P21/n (No. 14), with a = 13.3728(5) Å, b = 15.4281(7) Å, c = 17.4335(7) Å, β = 98.932(3)° and Z = 2. The unit cell contains two identical molecular clusters, each consisting of six interacting Cu2+ (S = ${1 \over 2}$) ions. Within the cluster the six oxygen‐bridged Cu2+ ions are arranged in an almost regular hexagon. An analysis of the high‐temperature part of the magnetic susceptibility reveals that the complex has a strong average ferromagnetic Cu–Cu exchange interaction of |Jav/kB| = (50.4 ± 1) K with a high‐spin S = 3 ground state. A satisfactory fit for the magnetic susceptibility and the magnetization in the whole accessible temperature range is obtained from a Heisenberg model with nonuniform exchange couplings within a ring, corresponding to a system of two weakly coupled trimers with a ferromagnetic intratrimer exchange coupling of |J/kB| = 72.5 K and a ferromagnetic intertrimer exchange coupling of |J′/kB| = 7 K. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)