Synthesis, spectroscopic properties and X-ray crystal structures of two dinuclear alkoxo-bridged copper(II) compounds with the ligand bis(1-methyl-2-benzimidazolyl) propane. A unique alkoxo-bridged Cu(II) dinuclear compound with an additional bidentate bridging triflate anion

Based on the new ligand bis(1-methyl-2-benzimidazolyl) propane (abbreviated as mtbz) several new copper(II) coordination compounds have been prepared and characterized structurally and spectroscopically. Two representative compounds, i.e. [Cu-2(mtbz)(2)(CH3O)(2)(CF3SO3)](CF3SO3) (1) and [Cu-2(mtbz)(2)(CH3O)(2)](ClO4)(2) (4) were characterized structurally by X-ray diffraction. Crystal data for 1: monoclinic, space group P2(1)/c, a = 13.6585(5), b = 39.981(3), c = 20.919(1) Angstrom, beta = 125.98(1)degrees, Z = 8. Crystal data for 4: monoclinic, space group P2(1)/c, a = 13.115(2), b = 9.523(2), c = 17.908(4) Angstrom, beta = 111.71(1)degrees, Z = 2. Structures 1 and 4 each consist of a dinuclear unit with bridging methoxo groups and one ligand linked to each copper via an N atom. Structure 1 (which consists of two dinuclear, crystallographically independent, but chemically identical units) has the two copper atoms bridged by a triflate anion, providing each copper atom a square-pyramidal coordination, while the copper atoms in structure 4 have an almost a square-planar geometry. The Cu-Cu distances (Angstrom) within the dinuclear units are: 1, 2.9775(13), 2.9751(13); 4, 2.9872(16); the Cu-O-Cu bridging angles (degrees) are: 1, 101.7(3), 101.7(3), 100.9(3), 102.1(3); 4, 103.2(2). The mid-IR section focused on the vibrations of the triflate anion reveals interesting results concerning the assignment of that anion related to the nu(as)(S-O) band. Characteristic Cu-O vibrations in the far-IR section were found at 386 and 230 cm(-1) for the methoxo-bridged and 454 and 332 cm(-1) for the ethoxo-bridged compounds. These dinuclear species are EPR silent, and only a weak signal of monomeric impurities is observed. They also show a diamagnetic behavior below room temperature.