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

Abstract

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(CH 3) 2- (CF 3SO 3)](CF 3SO 3) ( 1) and [Cu 2(mtbz) 2(CH 3O) 2](ClO 4) 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) A ̊ , β=125.98(1)°, Z=8 . Crystal data for 4: monoclinic, space group P2 1/ c, a=13.115(2), b=9.523(2), c=17.908(4) A ̊ , β=111.71(1)°, 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 (Å) within the dinuclear units are: 1, 2.9775(13), 2.9751(13); 4, 2.9872(16); the CuOCu bridging angles (°) 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 assignments of that anion related to the v 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.