Crystal structure, magnetism and spectroscopy of a dinuclear Cu(II) compound with a chiral ligand; Cu 2(SL)(μ-Cl)(Cl) 2(CH 3OH) (HSL = S-1,2-bis(benzimidazol-2-yl)-1-hydroxyethane)

Abstract

The dinuclear compound, Cu 2(SL)(μ-Cl)(Cl) 2(CH 3OH) (in which HSL is the chiral ligand S-1,2-bis(benzimidazol-2-yl)-1-hydroxyethane), has been synthesized and characterized by X-ray crystallography and infrared spectroscopy. In addition, EPR and magnetic measurements have been performed, and related to the dinuclear structural details. The compound crystallizes in the orthorhombic space group P2 12 12 1, with a = 6.1240(12) Å, b = 15.780(3) Å, c = 20.316(4) Å, V = 1963.3(7) Å 3 and Z = 4. The Cu1 ion has a distorted square-pyramidal geometry with the basal plane consisting of a nitrogen atom from the ligand with a Cu–N distance of 1.995(8) Å, a bridging oxygen atom of the ligand with a Cu–O distance of 1.943(8) Å and two chloride anions (of which one is bridging to Cu2) with Cu–Cl distances of 2.259(3) and 2.351(3) Å. The apical position is occupied by a third chloride atom (Cl3), which is also connected to Cu2 from a neighbouring unit, at a semi-coordinating distance of 3.114(3) Å. The second copper atom, Cu2, has also a distorted square-pyramidal geometry with the basal plane also consisting of a nitrogen atom from the ligand with a Cu–N distance of 1.960(8) Å, a bridging oxygen atom of the ligand with a Cu–O distance of 1.934(8) Å and two chloride atoms (of which one is bridging to Cu1) with Cu–Cl distances of 2.258(3) and 2.309(3) Å. The apical position is occupied by an oxygen atom of a coordinating methanol molecule at a distance of 2.392(3) Å. The bridging Cl3 atom, forms a zig-zag chain between Cu1 and Cu2 from different units forming an extended chain with a Cu⋯Cu distance of 4.2114(19) Å. The intramolecular Cu⋯Cu distance is 3.2301(18) Å. At room temperature the title compound displays an EPR silent behaviour and magnetic susceptibility measurements, down to 5 K, agree with a strong overall antiferromagnetic interaction having a large singlet-triplet splitting ( J = −348 cm −1).