COPPER(I) AND SILVER(I) COMPLEXES OF A NEW TETRAHEDRALLY-ENFORCING LIGAND CONTAINING 2 BIPYRIDYL BINDING-SITES LINKED BY A DIPHENYL DISULFIDE BRIDGE

Conversion of the amino group of 6-(2-aminophenyl)-2,2'-bipyridine to a thiol resulted not in the expected N,N,S-terdentate chelating ligand HL [6-(2-sulfhydryl)-2,2'-bipyridine] but in the oxidised disulfide 2 ,2'-bis[6-(2,2'-bipyridyl)]diphenyldisulfide, L-L. This ligand contain s two bipyridyl arms linked by a diphenyl disulfide bridge in such a w ay that they cannot be coplanar, but tend to co-ordinate to a single m etal ion with a substantial dihedral angle between the two ligand plan es giving a pseudo-tetrahedral geometry. The crystal structure of L-L . 0.5C(6)H(5)CH(3) shows the presence of near-linear N ... S-S interac tions (non-bonded N ... S; 2.75 Angstrom) in which the pyridyl lone pa ir interacts with the sigma orbital of the disulfide fragment. The co mplexes [Cu(L-L)][PF6] and [Ag(L-L)][PF6] were prepared and are isostr uctural, both having a distorted four-co-ordinate metal co-ordination environment in which the two chelating bipyridyl fragments have dihedr al angles of between 70 and 80 degrees C between them (ie. nearly mutu ally perpendicular). The electronic spectrum of the Cu-I complex [Cu(L -L)][PF6], and the EPR spectrum of its one-electron oxidised product [ Cu(L-L)](2+), both confirm that the rigidity of the ligand donor set d oes not permit much variation in the co-ordination environment about t he copper ion. The ligand therefore imposes a relatively rigid pseudo- tetrahedral geometry on the metal centres.