Approach to Anionic Alkaline Earth Metal-Methanesulfonates Bearing Photo-responsive Methylviologen

Abstract

Anionic coordination frameworks stabilized by methylviologen (MV; 1,1’-dimethyl 4,4’-bipyridinium) as photochromic module belong to a distinct class of functional materials. Herein, we report the first examples of alkaline earth metal-methanesulfonates, [MV{Mg(OSO2Me)3(H2O)2}2](1), [MV{Ca(OSO2Me)3(H2O)2}2] (2), [2{Mg(OSO2Me)2(H2O)4}MV·2OSO2Me] (3), and [Me4-pip{Ca2(OSO2Me)6(H2O)2}]n(4) incorporating methylviologen or tetra-N-methylpiperazinium (Me4-pip) as charge balancing cations. X-Ray crystallographic studies of 1-3 emphasize the role of isolated ion-pairs for the construction of hydrogen-bonded supramolecular assemblies as well as the ability of methanesulfonate as electron donor (centroid---O = 3.09-3.15Å) to promote photoinduced one electron reduction of MV to MV·+ radical cation in the solid state. The inorganic framework in 4 adopts a layered motif with inter-lamellar spacings of 11.8Å, providing spatial expanse to accommodate the organic cations.