New dinuclear transition metal complexes with the [M-2(mu-dhbq)](n+) core and 2-(2 '-pyridyl)quinoxaline (L) as a terminal ligand: Preparation and characterization (dhbq(2-) = the dianion of 2,5-dihydroxy-1,4-benzoquinone; M= Ag-I, Mn-II, Co-II, Ni-II, Cu-II, Ru-II, Pd-II, Fe-III, Rh-III; n = 0, 2, 4)

Synthetic procedures are described that allow access to the new complexes [ Mn-2(dhbq)L-2(H2O)(4) (1). [Fe-2(dhbq)L-2(H(2)o)(4)](NO3)(4). 6H(2)O (2). [ Co-2(dhbq)Cl2L2(H2O)(2)] (3). [Ni-2(dhbq)Cl2L2(H2O)(2)] (4). [Cu-2(dhbq)Cl2 L2(H2O)(2)] (5). [Ru-2(dhbq)L-2(H2O)(4)](ClO4)(2) (6). [Rh-2(dhbq)Cl2L2(H2O )(2)]Cl-2. 2H(2)O (7), [Pd-2(dhbq)L-2]Cl-2. 5H(2)O (8) and [Ag-2(dhbq)L-2] (9). where dhbq(2-) is the dianion of 2,5-dihydroxy-1,4-benzoquinone and L is the biheteroaromatic ligand 2-(2 ' -pyridyl)quinoxaline. The new complex es were characterized by elemental analyses and by a variety of physical an d spectroscopic techniques. Dinuclear structures are assigned for the compl exes in the solid state. The two metal ions are bridged by the bischelating dhbq(2-) ion, while L behaves as a bidentate chelate with the 2 ' -pyridyl nitrogen and the nearest quinoxaline nitrogen atom as the ligand atoms. Th e metal ion coordination geometries are octahedral, tetrahedral or square p lanar.