Solar Energy Storage Reactions. Determination of the Structure of the Complex Formed by Visible Irradiation of Rh2(bridge)42+ in Aqueous HC1 Solutions

Visible irradiation of Rh2 (bridge)42+ in concentrated HC1 solutions yields hydrogen gas and a yellow complex, Rh2(bridge)4Cl22+. An X-ray crystal structure analysis of [Rh2(bridge)4Cl2]Cl2-8H20 (bridge=1,3-diisocyanopropane) has been completed (final RF=0.031). The complex crystallizes in the space group [formula omitted]. The structure is composed of Rh2(bridge)4Cl22+ cations having approximate D4h symmetry and a hydrogen-bonded network of CI” anions and water molecules. Each Rh atom is six-coordinate with CI and Rh atoms in axial positions of a Cl(RhC4) Rh unit. The RhRh distance in the binuclear cation is 2.837 (1) υ, and RhCl is 2.447 (1) υ. The relative ease of reductive elimination of X from Rh2(bridge)4X22+ (×=CI, Br) complexes may be explained in part by the drive to reduce CC' and NN' nonbonded-atom repulsions that are caused by the close approach (—2.85 υ) of the Rh(CN)4 planes.