3-CO-ORDINATE AND 4-CO-ORDINATE COPPER(I) COMPLEXES-1 1 AND 1/2 1-CYANOGUANIDINE-COPPER(I) HALIDE ADDUCTS/

The air- and moisture-stable copper(I) complexes Cu2X2-cnge and CuX.cn ge.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 aq ueous solutions of CuX2 (X = Cl or Br) containing cnge with sodium sul fite. Single crystals of Cu2Cl2.cnge 1, Cu2Br2.cnge 2 and CuBr.cnge-H2 O 3 were obtained from the latter route. Complexes 1 and 2 are isostru ctural and comprise mutually perpendicular chains of [XCu(cnge)]n and (CuX2-)n joined at a common halogen. The [XCu(cnge)]n chain, which lie s in the mirror plane of the Pbcm space group, is novel. The cyanoguan idine molecule uses both its nitrile and imino nitrogen atoms to bridg e the copper atoms which complete their co-ordinatively unsaturated, t rigonal-planar, geometry with the common halogen. The (CuX2-)n chain i s unremarkable. Complex 3 is characterised by a zigzag (CuBr)n chain a nd a buckled [BrCu(cnge)]n chain joined at a common copper atom; an un co-ordinated water molecule completes its structure. The [BrCu(cnge)]n chain is similar to that in 1 and 2. The main difference is the buckl ing which results in a dihedral angle between adjacent cnge molecules of 8.9-degrees. The (CuBr)n chain consists of bridging bromine atoms s trongly bonded to one copper and weakly bonded to the other, giving a trigonal-pyramidal copper(I) co-ordination sphere. Extended-Huckel cal culations have been used to examine the factors controlling the choice of a trigonal-planar over a tetrahedral structure.