Mixed-valency with cyanides as terminal ligands: Diruthenium(III,II) complexes with the 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine bridge and variable co-ligands (CN- vs. bpy or NH3). Inorganica Chimica Acta, (363)1:163--167, 2009. [PUMA: bis complex cyanides diruthenium ligand mixed pyridyl terminal valency]