Synthesis and mixed valence aspects of [{(L)ClRu}2(μ-tppz)]n+ incorporating 2, 2′-dipyridylamine (L) as ancillary and 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) as bridging ligand

The tppz-bridged diruthenium complex [{(L)ClRuII}(2)(mu-tppz)](ClO4)(2), [1](ClO4), {tppz=2,3,5,6-tetrakis(2-pyridyl)-pyrazine, L=2,2'-dipyridylamine} and its mononuclear counterpart [(L)ClRuII(tppz)]ClO4, [2](ClO4) have been synthesized. The 380 mV separation between successive Ru-II/Ru-III couples in [1](2+) leads to a comproportionation constant (K-c) of 2.7x10(6). Consequently, the (RuRuIII)-Ru-II species [1](3+) exhibits a rather narrow intervalence charge transfer band at 1700 run, suggesting a class III mixed-valence state, the electronic coupling constant (V-ab) is calculated at 2940 cm(-1). Complex [1](3+) displays a rhombic EPR spectrum at 4 K (g(1)=3.390, g(2)=2.278, g(3)=1.697), characteristic of ruthenium(III) in a distorted octahedral environment. Both complexes show two successive tppz-based reduction processes [(tppz)(0/-1) and (tppz)(-1/-2)]. The one-electron reduced species [1](+) is a tppz radical anion species with an intense low-energy band at 1105 nm and an axial EPR signal at 4 K (g(1)=2.008, g(2)=g3=1.994). [1](2+) and [2](+) exhibit moderately strong emissions at 740 nm and 668 nm, respectively, in EtOH-MeOH glass at 77 K.