Host–guest chemistry between cyclodextrin and hydrogen evolution catalyst of cobaloxime

We report host–guest chemistry between cyclodextrins and a bisdimethylglyoximato cobalt complex, cobaloxime. The cobaloxime forms 1:1 host–guest assembly with β- or γ-cyclodextrin but not with α-cyclodextrin. The assembly of the cobaloxime with γ-cyclodextrin enhances the photocatalytic hydrogen evolution activity of a homogeneous system that contains an organic dye of eosin Y in a neutral aqueous solution under visible-light irradiation.