Synthesis of anionic alkaline earth metal methanesulfonates bearing photo-responsive methylviologen.

Anionic coordination frameworks stabilized by methylviologen (MV; 1,1'-dimethyl 4,4'-bipyridinium) as a photochromic module are a distinct class of functional materials. Herein, we report the first examples of alkaline earth metal methanesulfonates [MV{Mg(OSOMe)(HO)}] (1), [MV{Ca(OSOMe)(HO)}] (2), [2{Mg(OSOMe)(HO)}MV·2OSOMe] (3), and [Me-pip{Ca(OSOMe)(HO)}] (4) incorporating methylviologen or tetra--methylpiperazinium (Me-pip) as a charge-balancing cation. X-ray crystallographic studies of 1-3 emphasize the role of isolated ion-pairs for the construction of hydrogen-bonded supramolecular assemblies and the ability of methanesulfonates to donate electrons (centroid⋯O = 3.09-3.15 Å) to promote photoinduced one-electron reduction of MV to an MV˙ radical cation in the solid state. The inorganic framework in 4 adopts a layered motif with an inter-lamellar spacing of 11.8 Å, providing spatial expanse to accommodate the organic cations.