COMPARISON OF THE PROPERTIES OF THE 4,5,5-HEXACYANO-3-AZA-PENTA-1,4-DIENIDE[(NC)(2)C=C (CN)-N-C(CN)=C(CN)(2)] UNIT AS ANION AND AS LIGAND -CRYSTAL-STRUCTURES OF (ET(4)N)(C10N7) AND [(AG(C10N7))(INFINITY)]

The previously reported compounds, Et(4)N(C10N7), 1, and [(Ag(C10N7)}( infinity)], 2, have been structurally characterized by X-ray diffracti on. The C10N7 unit acts in 1 as a monoanion and in 2 as a sophisticate d bridging ligand (via the nitrogen atoms of its four external cyanogr oups) leading to a structure with two crystallographically distinct si lver cations. The first one has an usual pseudo-tetrahedral coordinati on, the second one presents an unexpected square planar coordination w hich is discussed. The geometry of the organic fragment is only slight ly modified upon coordination: in both cases, the C10N7 unit is essent ially planar with central CN bond lengths of 1.317(4) and 1.334(4) Ang strom in 1, 1.33(1) and 1.34(1) Angstrom in 2 and CNC angles of 128.3( 3) in 1 and 129.2(9)degrees in 2. In benzonitrile solutions, the C10N7 anion shows two one electron diffusion-controlled reversible reductio n processes, the first one leading to the radical species [(C10N7)(.)] (2-) characterized by ESR.