Cobalt(II) and nickel(II) halide coordination compounds with 1,6-bis(benzimidazol-2-yl)-2, 5-dithiahexane and 1,7-bis(benzimidazol-2-yl)-2, 6-dithiaheptane. The crystal and molecular structure of dibromo(1,6-bis(benzimidazol-2-yl)-2,5-dithiahexane)nickel(II)

Abstract

The synthesis and characterization by spectroscopic techniques of compounds with general formulae MX 2(bbdh) and MX 2(bbdhp) is described. In these formulae M = Co(II), Ni(II); X = Cl, Brbbdh = 1,6-bis(benzimidazol-2-yl)-2,5-dithiahexane and bbdhp = 1,7-bis(benzimidazol-2-yl)-2,6-dithiaheptane. The compounds have been characterized by chemical analysis, infrared spectra, ligand field spectra, X-ray powder diagrams and in one case by a single crystal structure analysis. The metal ions are octahedrally (all Ni compounds and the Co compound of bbdh) or tetrahedrally (Co compounds of bbdhp) coordinated by the ligands and the anions. The detailed structure of NiBr 2(bbdh) was determined by X-ray methods at 290 K. Crystals of C 18H 18Br 2N 4NiS 2, M r = 572.995, crystallized in the orthorhombic space group Pnc2, with a = 8.502(3), b = 13.748(2), c = 8.794(3) Å, V = 1027.96(57) Å 3, Z = 2, D x = 1.851 Mg/m 3, were studied with CuKα radiation (using monochromator, λ = 1.54178 Å), μ(CuKα) = 7.931 mm −1, F(000) = 568. The final conventional R-factor = 0.064, (R w = 0.083) for 1600 “observed” reflections and 122 variables. The structure was solved using Patterson and DIRDIF techniques and refined by SHELX. The coordination around Ni(II) is octahedral with a cis-geometry of the two bromide anions (NiBr = 2.543(2) Å), a trans-arrangement of the benzimidazole ligands (NiN = 2.132(8) Å) and a cis-geometry of the thioether groups (NiS = 2.441(3) Å). The packing in the crystal results in hydrogen bond interactions between the N-H groups of the imidazoles and bromine atoms of nearby units. The structures of the nickel compounds and the isomorphous Co(II) bbdh compound are believed to be essentially the same, as deduced from spectroscopic analysis. The Co(II) compounds of bbdhp, however, appear to be tetrahedrally coordinated, as deduced from ligand field spectra. It seems that in this case the thioether groups are not coordinated to the Co(II) ion.