Structure determination, spectroscopic characterization, and magnetic properties of a novel dinuclear copper(II) crown ether bipyridine complex

The synthesis of a novel ligand system (1) composed of two bipyridine units linked by a crown ether moiety is described. Addition of 2 equiv of [Cu(MeCN) ₄ ]BF ₄ to 1 and subsequent oxidation yield a dinuclear µ-hydroxo-bridged copper(II) complex, [(1)Cu ₂ (OH) ₂ BF ₄ ]BF ₄ ·2H ₂ O (2). The structure of this complex has been determined by X-ray crystallographic methods. Crystal data: triclinic, space group P1̅ (No. 2), a = 10.060(1)Å,b = 12.747(2) Å, c = 16.787(1) Å, a = 92.01(1)°, β = 103.01(2)°, y = 104.01(2)°. The Cu-O-Cu angles in complex 2 are nonequivalent (94.8 and 98.4°). One of the coppers is pentacoordinated; the other is hexacoordinated. Two molecules of 2 are linked by hydroxo ligands, forming a tetranuclear complex in which the Cu ₂ (OH) ₂ units have parallel but shifted positions. Magnetic susceptibility and EPR measurements suggest that complex 2 has a triplet ground state, with a triplet-singlet energy gap of 16 cm ⁻¹ .