BIS(MU-2-CYANOGUANIDINE)-BIS[(2-CYANOGUANIDINE)COPPER(I)] - A PLANAR DIMERIC CATION CONTAINING COORDINATIVELY UNSATURATED COPPER(I)

The air- and moisture-stable copper(I) salts [Cu-2(mu-cnge)(2)(cnge)(2)]X . 2H(2)O (cnge = 2-cyanoguanidine; X = S2O62- or SO42-) have been prepared by sodium sulfite reduction of aqueous solutions of copper(II) chloride containing cnge. The two salts have been structurally characterised by single-crystal X-ray diffraction methods. The dithionate structure (triclinic, space group P ($) over bar 1, a = 7.320, b = 7.315, c =12.765 Angstrom, alpha = 97.10, beta = 118.91, gamma = 92.93 degrees) is more symmetrical than that of the sulfate (monoclinic, space group P2(1)/c, a = 6.920, b = 14.951, c = 21.042 Angstrom, beta = 95.17 degrees). Nonetheless, the two [Cu-2(mu-cnge)(2)(cnge)(2)](2+) cations are very similar. They contain two trigonal-planar copper(I) atoms bridged by two cnge molecules and terminally co-ordinated by a single cnge molecule. To minimise interaction between the in-plane pi systems of the bridging cnge molecules, the latter are separated by ca. 3.1 Angstrom and angled such that they lie on two essentially parallel planes separated by ca. 0.75 Angstrom. The perturbation of the IR spectrum of cnge on co-ordination is dependent not on the co-ordination type (bridging, terminal) but on the strength of its co-ordination to the metal.