Copper(II) and zinc(II) co-ordination compounds of tridentate bis(benzimidazole)pyridine ligands. Crystal and molecular structures of bis[2,6-bis(1′-methylbenzimidazol-2′-yl)pyridine]copper(II) diperchlorate monohydrate and (acetonitrile)[2,6-bis(benzimidazol-2′-yl)pyridine](perchlorato)copper(II) perchlorate

Abstract

Compounds are described of general formulae Cu(L¹)X₂, Cu(L¹)₂X₂, Cu(L²)X₂, and Cu(L²)₂X₂ with L¹= 2,6-bis(benzimidazol-2′-yl)pyridine, L²= 2,6-bis(1′-methylbenzimidazol-2′-yl)pyridine, and X = Cl, Br, or ClO₄. For comparison also a few zinc(II) halides were prepared and characterized. The compounds were structurally characterized by i.r., ligand-field, and e.s.r. spectra and for two representative cases [Cu(L¹)(CH₃CN)(ClO₄)][ClO₄](1) and [Cu(L²)₂][ClO₄]₂·H₂O (2) also by X-ray diffraction techniques. Compound (1) crystallizes in space group P2₁/c with a= 14.061(1), b= 20.638(1), c= 8.273(1)Å, β= 101.119(8), and Z= 4; R= 0.0366 for 4 265 observed reflections with I > 2σ(I). Compound (2) crystallizes in space group P2₁/c with a= 8.4824(22), b= 29.1965(29), c= 16.7393(24)Å, β= 95.836(17)°, and Z= 4; R= 0.062 for 3 165 observed reflections with I > 3σ(I). The structure of (1) consists of one tridentate chelating L¹ ligand and CH₃CN, co-ordinated in a square-planar geometry (Cu–N 1.96–2.03 Å) with a perchlorato oxygen at 2.40 Å, thereby completing a five-co-ordinate geometry. A sixth ligand at 2.8 Å(from another perchlorate oxygen) is considered to be semico-ordinating. The structure of (2) consists of one tridentate and one bidentate L², chelating in a five-co-ordinate geometry, again tetragonal pyramidal, with the apical ligand (Cu–N 2.51 Å) coming from the bidentate chelating L². The sixth donor atom, again from a perchlorate oxygen, at 2.70 Å is considered to be semi-co-ordinating. Spectroscopic and magnetic data have been used to deduce structures for the other copper(II) compounds based on these two X-ray structures.