MOLECULAR-STRUCTURES AND CRYSTAL-STRUCTUR ES OF 2 MONONUCLEAR RUTHENIUM(II) COMPLEXES WITH THE STRONGLY PI-ACCEPTING LIGAND 2,2'-AZOBIS(PYRIDINE) (ABPY) - [MER-RU(ABPY)(3)](PF6)(2) AND RU(ABPY)(2)CL-2 (CTC ISOMER)

Crystal structure analyses of the title complexes have been carried ou t in order to establish their molecular configurations. The tris(chela te) complex dication in (1)(PF6)(2) exhibits a mer configuration of py ridine and azo nitrogen atoms in an approximately octahedral arrangeme nt at the metal. The dichlororuthenium bis(chelate) compound 2 has the halide ligands and the coordinated azo nitrogen centers in an equator ial cis arrangement whereas two pyridyl groups (one of each abpy ligan d) occupy the axial positions. The bond distances from the metal to th e nitrogen donor centers are systematically smaller for the stronger p i accepting azo functions than for the more basic but less pi acidic p yridyl groups, a result which differs from that obtained for Mo(0) and Cu(I) complexes of abpy. All Ru-N distances are shorter in the neutra l dichloro complex 2. The non-coordinated pyridyl rings of the potenti ally tetradentate abpy ligands are tilted into approximate s-cis/(NN-t rans)/s-trans positions (dihedral angle omega approximate to 145 degre es) as to minimize steric repulsion. however, they do not coordinate t o the metal (d(Ru-N) > 327 pm). While there are no significant intermo lecular interactions, the observed conformation implies that considera ble structural reorganization is necessary for the formation of oligon uclear complexes.