Photochemical and photocatalytic properties of adsorbed organometallic compounds. 2. Structure and photoreactivity of tris(2,2'-bipyridine)ruthenium(II) and -chromium(III) at the solid-gas interface on hectorite

The structure of Ru(bpy)/sub 3//sup 2 +/ and Cr(bpy)/sub 3//sup 3 +/ (bpy = 2,2'-bipyridine) adsorbed in the interlamellar space of hectorite - an expanding layer lattice silicate - has been studied by IR and XPS spectroscopy. The adsorbed complexes appear to be slightly distorted, with weaker Ru-N bonds and stronger Ru-H/sub 2/O interactions than in pure Ru(bpy)/sub 3/Cl/sub 2/6H/sub 2/O and Cr(bpy)/sub 3/(ClO/sub 4/)/sub 3/./sup 1///sub 2/H/sub 2/O. The positive charge on the Ru nucleus in the adsorbed Ru complex is singificantly higher than in its solid-state chloride salt. The pseudo C/sub 3/ axis of Ru(bpy)/sub 3//sup 2 +/ is perpendicular to the silicate sheets, whereas the pseudo C/sub 3/ axis of Cr(bpy)/sub 3//sup 3 +/ is nearly parallel to them. The photoreactivity of adsorbed Cr(bpy)/sub 3//sup 3 +/ has been studied at room temperature. The basic reaction is photoaquation, but the nature of the photoproducts, the kinetics of photoaquation and also the reversibility of the reaction are dependent on the hydration state of the clay surface. Ru(bpy)/sub 3//sup 2 +/-hectorite samples are photoinert at room temperature, but irradiation at higher temperature leads to the formation of Ru(III) oxo-bridged dimers. The reaction mechanism appears to be photoaquation, followed by a purely thermal, and partially reversible, oxidation-dimerization reaction. The nature of the reactive excited state is discussed in the light of the spectroscopic data.