Thermal decomposition of mixed-valent diruthenium pentakis(alkanoates) enhanced by their liquid crystalline state

Abstract

The thermal decomposition of mixed-valent diruthenium pentakis(alkanoates) of general formula Ru 2 (II,III)(O 2C(CH 2) n−2 CH 3) 5 (for n=3, 4, 5, 6, 8, 10, 12, 16), studied by a combination of several complementary physicochemical techniques, has been found to take place in two differentiated steps. The first one gives the divalent analogues Ru 2 (II,II)(O 2C(CH 2) n−2 CH 3) 4 as the main product, in a one-electron reduction of the bimetallic core likely provided by oxidative decarboxylation of the axial anion. The second one involves the reduction of the binuclear core to metallic ruthenium, and the oxidation of the equatorial carboxylates. The first step is very much influenced by the aggregation state of the system, the occurrence of a liquid–crystalline phase in compounds with n>6 facilitates the thermolysis: decomposition temperatures fall from ≈300°C for compounds with n=3 to ≈175°C for compounds with n=10–16.