The monometallic complexes [(bpy)2Ru(tpphz)]2+ (4) and [(bpy)2Os(tpphz)]2+ (5), where tpphz is the poorly soluble fully aromatic tetrapyrido[3,2-a:2‘,3‘-c:3‘‘,2‘‘-h:2‘‘‘,3‘‘‘-j]phenazine, have been obtained by reaction of 5,6-diamino-1,10-phenanthroline with [(bpy)2M(phendione)]2+ (M = RuII or OsII). Reaction of 4 and 5 with metallic precursors yielded the homo- and heterobimetallic complexes [(bpy)2Ru(tpphz)Ru(NH3)4]4+ (6), [(bpy)2Ru(tpphz)Ru(bpy)2]4+ (7), [(bpy)2Os(tpphz)Os(bpy)2]4+ (8), and [(bpy)2Ru(tpphz)Os(bpy)2]4+ (9). The mononuclear 4 and 5 aggregate in solution, probably by π−π stacking of the tpphz part as shown from proton NMR. The complexes show one reversible metal-centered oxidation and several reversible (except 6) reductions which add one electron on the tpphz ligand, one electron on one bpy of each metallic end, a second electron on one bpy of each metallic end, and then a second electron on the tpphz ligand. The complexes (except 8) are luminescent in acetonitrile. Quenching of the luminescence by water has been attributed to proton quenching at the phenazine nitrogen atoms.

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The three isomers of diferrocenylbenzenes (ortho, 1o; meta, 1m; para, 1p) as well as 5-substituted derivatives of m-diferrocenylbenzene with R ) NH 2 (2), Cl (3), CH 3 (4), CN (5), NO 2 (6), and N(CH 3 ) 3 3+ (7) have been prepared. Crystal structures of 1o, 3, and 5 have been solved. In 3 and 5, the cyclopentadienyl rings are nearly parallel to the benzene mean planes with angles ranging from 9.99(5)°to 14.74(5)°. One ferrocene group is above and the other below the mean molecular plane. For 1o, there is an important twist between the benzene and cyclopentadiene rings (68.6(8)°and 32.5(8)°) for steric reasons. Controlled potential electrolysis yields the mixed-valence ferrocene/ ferrocenium species in comproportionation equilibrium with homovalent species. Intervalence transitions have been observed and corrected from comproportionation. From the intervalence band parameters, metal-metal couplings (V ab ) are calculated using Hush's equation. The values are much higher for 1o (0.025 eV) and 1p (0.043 eV) than for 1m (0.012 eV) and exhibit little or no variation for the substituted m-diferrocenylbenzenes 2-6. These results are rationalized by extended Hu ¨ckel molecular orbital calculations. The weakness of the interaction in 1m can be ultimately traced to a quantum Interference effect, i.e., a cancellation of the contributions of two electron transfer paths. This cancellation occurs because each path implies a mixing of metal orbitals with a different ligand orbital, and the resulting molecular orbitals exhibit different symmetries.