Fused N-Heterocyclic-Bridged Isomeric Diruthenium Complexes [(acac)Ru(μ-DIPQD)Ru(acac)], = +2, + 1, 0, -1, -2.

π-Conjugated bridged isomeric diruthenium(II) complexes [(acac)Ru(μ-DIPQD)Ru(acac)], () and () (acac = acetylacetonate, (8,16)-,-diphenylindeno[1,2-]indeno[2',1':5,6]pyrazino[2,3-]quinoxaline-8,16-diimine (-DIPQD), and (12,16)-,-diphenylindeno[1,2-]indeno[1',2':5,6]pyrazino[2,3-]quinoxaline-12,16-diimine (-DIPQD) were separated and structurally characterized. The structures of the (ΔΔ/ΛΛ) forms of and exhibit two units of {Ru(acac)}, linked to adjacent pyrazine and imine nitrogen donors of the bridge (DIPQD) in and modes, with metal-metal separations of 9.050 and 6.330 Å, respectively. The packing diagrams of and revealed an intermolecular π···π stacking interaction (3.202-3.398 Å) 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 brick-layer stacking in the latter. The electronic forms associated with multiple reversible one-electron redox steps of and 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 and , viz., primarily metal-based oxidations ([(acac)Ru(μ-DIPQD)Ru(acac)], /, = 1/2; [(acac)Ru(μ-DIPQD)Ru(acac)], /, = 1) and bridge-based reductions ([(acac)Ru(μ-DIPQD)Ru(acac)], /, = 1/2; [(acac)Ru(μ-DIPQD)Ru(acac)], /, = 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 (∼2000 nm) in /.