STRUCTURE OF TRANS-M(CO)(C4N3)(PPH3)2.1.5C6H6 (M = IR AND RH) - THE PYRAMIDAL GEOMETRY OF THE TRICYANOMETHANIDE ANION (C4N3-)

The crystal structures of two tricyanomethanide (TCM) complexes have b een determined. Compound (1), ne)carbonyl(2,2-di-cyanoethylideneamino) iridium(I) (the ligand 2,2-di-cyanoethylideneamino = TCM), was studied at both 298 K (RT) and 135 K (LT). Crystal data: triclinic, a = 11.54 9 (3), b = 12.528 (2), c = 16.931 (2) angstrom, alpha = 91.13 (1), bet a = 99.45 (2), gamma = 114.87 (2)degrees, final R = 0.039 and wR = 0.0 54 for the RT structure, and triclinic, a = 11.330 (4), b = 12.337 (4) , c = 16.908 (4) angstrom, alpha = 91.61 (2), beta = 99.60 (3), gamma = 114.48 (3)degrees, final R = 0.036 and wR = 0.046 for the LT structu re. The RT structure of (2), e)carbonyl(2,2-dicyanoethylidene-amino)rh odium(I), is very similar to the RT structure of (1). Crystal data: tr iclinic, a = 11.759 (3), b = 11.779 (5), c = 16.352 (3) angstrom, alph a = 102.21 (2), beta = 104.61 (2), gamma = 94.92 (3)degrees, final R = 0.070 and wR = 0.079. In both cases the TCM ligand is coordinated to the metal, near linearly through nitrogen, and both metal centers have a distorted square-planar geometry. In the RT structure, the geometry of TCM is planar with one set of unusually large displacement paramet ers for one of the cyano groups. In the LT structure of (1), these lar ge anisotropic displacement parameters were resolved into half-populat ed C and N sites of disordered cyano groups. The geometry of TCM is th us slightly pyramidal, with the central C atoms lying 0.115 angstrom o ut of the plane defined by the three C atoms (C1, C2, C431) bonded to it.