SYNTHESIS AND CHARACTERIZATION OF TETRAAMMINERUTHENIUM(II) COMPLEXES BOUND TO THE BRIDGING LIGAND 3,6-BIS(2-PYRIDYL)1,2,4,5-TETRAZINE (BPTZ) - COMPARATIVE EFFECTS OF SIGMA AND PI PERIPHERAL LIGANDS ON ELECTRONIC ABSORPTION AND ELECTROCHEMICAL PROPERTIES

Tetraammineruthenium(II) complexes with the nitrogen aromatic heterocyclic bridging ligand 3,6-bis(2-pyridyl)1,2,4,5-tetrazine (bptz) have been prepared and characterized. The [{NH3)4Ru}(bptz)]2+ ion exhibits intense electronic MLCT transitions at 560(sh) and 479 nm, and for the [{(NH3)4Ru}2(bptz)]4+ ion MLCT transitions occur at 850(sh), 603 and 370 nm. Reversible metal oxidations for the bimetallic complex are at +1.56 and +0.72 V versus SCE and DELTA-E(2-1) = 840 mV indicates a large degree of ruthenium-ruthenium communication occurs through the bptz bridging ligand. The energies of the MLCT transitions and electrochemical potentials are compared with those for the analogous bis-bipyridyl ruthenium bptz complexes to assess the effect of NH3 sigma versus bpy pi non-bridging ligands. In these complexes, as well as others, the results show the ruthenium centers coordinated with NH3 are comparatively pi electron rich when compared with the analogous bpy complexes. H-1 and C-13 NMR data are reported for the bptz ligand and mono and bimetallic complexes.