Synthesis, Structure and Magnetic Properties of a Novel Linear Cu II ‐Trimer Complex

A new hexanuclear copper( II ) sandwich complex based on two 10‐membered macrocyclic phenylsiloxanolate ligands, {Cu 6 [(C 6 H 5 SiO 2 ) 5 ] 2 (OH) 2 (C 10 H 8 N 2 ) 2 } · 4(DMF) · 3(H 2 O) ( 1 ), was synthesized and characterized by single‐crystal X‐ray diffraction and measurements of the magnetic susceptibility and isothermal magnetization. The cluster compound crystallizes in the triclinic system, space group P $\bar {1}$ (No. 2), with a = 14.925(3) Å, b = 16.745(2) Å, c = 23.053(3) Å, α = 83.079(9)°, β = 84.836(13)°, γ = 65.019(17)°, and Z = 2. The unit cell contains two identical molecules, each consisting of six interacting Cu 2+ ( S = 1/2) ions. Within the molecule, the six Cu 2+ ions are arranged in two almost linear, parallel trimers. While pairs of oxygen atoms link the Cu 2+ ions within the trimers, single oxygen atoms residing at the ends of the trimers provide the strongest intertrimer bonds. Magnetic measurements reveal an antiferromagnetic intra trimer exchange interaction, J / k B = 85 K, as the dominant magnetic coupling of the complex. By introducing a weak antiferromagnetic inter trimer coupling, J′/k B = 3.5 K, a satisfactory description of the magnetic behavior over a wide range of temperature and magnetic field is obtained. The departure of the model curves from the data at the lowest available temperature indicates the presence of additional, weak intra ‐ and/or inter molecular interactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)