Three- and four-co-ordinate copper(I) complexes: 1:1 and 1:2 1-cyanoguanidine–copper(I) halide adducts

Abstract

The air- and moisture-stable copper(I) complexes Cu₂X₂·cnge and CuX·cnge·H₂O (X = Cl, Br or I) have been prepared by direct reaction of CuX and 1-cyanoguanidine (cnge) in organic solvents and by reduction of aqueous solutions of CuX₂(X = Cl or Br) containing cnge with sodium sulfite. Single crystals of Cu₂Cl₂·cnge 1, Cu₂Br₂·cnge 2 and CuBr·cnge·H₂O 3 were obtained from the latter route. Complexes 1 and 2 are isostructural and comprise mutually perpendicular chains of [XCu(cnge)]_n and (CuX₂^–)_n joined at a common halogen. The [XCu(cnge)]_n chain, which lies in the mirror plane of the Pbcm space group, is novel. The cyanoguanidine molecule uses both its nitrile and imino nitrogen atoms to bridge the copper atoms which complete their co-ordinatively unsaturated, trigonal-planar, geometry with the common halogen. The (CuX₂^–)_n chain is unremarkable. Complex 3 is characterised by a zigzag (CuBr)_n chain and a buckled [BrCu(cnge)]_n chain joined at a common copper atom; an unco-ordinated water molecule completes its structure. The [BrCu(cnge)]_n chain is similar to that in 1 and 2. The mam difference is the buckling which results in a dihedral angle between adjacent cnge molecules of 8.9°. The (CuBr)_n chain consists of bridging bromine atoms strongly bonded to one copper and weakly bonded to the other, giving a trigonal-pyramidal copper(I) co-ordination sphere. Extended-Hückei calculations have been used to examine the factors controlling the choice of a trigonal-planar over a tetrahedral structure.