Change of electrical conductivities between hydrated, dehydrated samples of honeycomb sheet structures with mixed oxidation state paddlewheel dirhodium complexes, halide ions

摘要

A series of mixed oxidation state compounds, [{Rh _2(acam) _4} _3(μ _3-X) _2]·nH _2O (Hacam = acetamide; X = Cl, n = 4 (1·4H _2O); X = Br, n = 10 (2·10H _2O); X = I, n = 10 (3·10H _2O)) and [{Rh _2(pram) _4} _3(μ _3-X) _2]·6H _2O (Hpram = propionamide; X = Cl (4·6H _2O), Br (5·6H _2O), I (6·6H _2O)) were synthesized and their X-ray structures were determined. In the crystal structure of all of these complexes, dirhodium complexes and halide ions construct 2-D honeycomb sheet arrangements in which the walls consist of Rh _2 units and halide ions lie at the corners. Complexes 1·4H _2O, 4·6H _2O, 5·6H _2O and 6·6H _2O have three independent Rh _2 units, in which there are two Rh _2 ~(5+) and one Rh _2 ~(4+). In these structures, the water molecules hydrogen bond to O atoms and from the N atoms of the amidate ligands. The number of hydrogen bonds from water molecules to the Rh _2 ~(4+) unit is greater than that to the Rh _2 ~(5+) units. This suggests that there exists pinning of the oxidation states by water molecules. In the structures of 2·10H _2O and 3·10H _2O, all of the Rh _2 units are crystallographically equivalent. In these structures, eight of the 10 water molecules form a honeycomb-like network between the {Rh _2(acam) _4} _3X _2 honeycomb sheets. The former four structures show very low electrical conductivities of ca. 10 ~(-8) S cm ~(-1) (room temperature, pellets) and the latter structures have the higher values of ca. 10 ~(-4) S cm ~(-1). In the former complexes, improvement of the values to 10 ~(-6) S cm ~(-1) was observed, caused by loss of pinning water.