Fused N-Heterocyclic-Bridged Isomeric Diruthenium Complexes [(Acac)(2)Ru(Mu-Dipqd)Ru(Acac)(2)](N), N =+2,+1, 0,-1,-2

pi-Conjugated bridged isomeric diruthenium(II) complexes [(acac)(2)Ru-II(mu-DIPQD)Ru-II(acac)(2)], 1 (trans) and 2 (cis) (acac(-) = acetylacetonate, (8E,16E)-N-8 ,N-16-diphenylindeno[1,2-b]indeno[2',1':5,6]pyrazino[2,3-g]quin-oxaline-8,16-diimine (trans-DIPQD), and (12E,16E)-N-12,N-16-diphenylindeno[1,2- b]indeno[1',2':5,6]pyrazino[2,3-g]quinoxaline-12,16-diimine (cis-DIPQD) were separated and structurally characterized. The structures of the rac (Delta Delta/Lambda Lambda) forms of 1 and 2 exhibit two units of {Ru(acac)(2)}, linked to adjacent pyrazine and imine nitrogen donors of the bridge (DIPQD) in trans and cis modes, with metal- metal separations of 9.050 and 6.330 angstrom, respectively. The packing diagrams of 1 and 2 revealed an intermolecular pi...pi stacking interaction (3.202-3.398 angstrom) involving the face-to-face arrangement of the aromatic rings of DIPQD in adjacent molecules and varying solid-state packing modes, slipped stacking in the former versus bricklayer stacking in the latter. The electronic forms associated with multiple reversible one-electron redox steps of 1 and 2 were addressed by DFT (MO composition, Mulliken spin density distribution), supported by EPR of intermediate paramagnetic states and by UV-vis-NIR spectroelectrochemistry in all redox states. The results reveal similar electronic forms along the redox series irrespective of their isomeric identities in 1 and 2, viz., primarily metal-based oxidations ([(acac)(2)Ru-II(mu-DIPQD)Ru-III(acac)(2)](+), 1(+)/2(+), S = 1/2; [(acac)(2)Ru-III(mu-DIPQD)Ru-III(acac)(2)](2+), 1(2+)/2(2+), S = 1) and bridge-based reductions ([(acac)(2)Ru-II(mu-DIPQD(center dot-))Ru-II(acac)(2)](-), 1(.-)/2(.-), S = 1/2; [(acac)(2)Ru-II(mu-DIPQD(2-))Ru-II(acac)(2)](2-), 1(2-)/2(2-), S = 1). TD-DFT analysis of the electronic transitions in the complexes suggests bridge-targeted mixed metal/ligand-based multiple charge transfer transitions over the visible to NIR region in all redox states, while a weak band involving the radical bridge appeared in the long-wavelength region (similar to 2000 nm) in 1(.-)/2(.-).