C 10 H 6 NO 2 Cd(NO 3 )·2H 2 O: a birefringent crystal with an enlarged band-gap derived from covalent edge-sharing connection.

A new birefringent crystal, C 10 H 6 NO 2 Cd(NO 3 )·2H 2 O, was designed by combining a π-conjugated [C 10 H 6 NO 2 ] - group with a CdO 7 N polyhedron. Notably, the experimental energy gap is 0.02 eV higher than that of the organic raw material, which resulted from a covalent edge-sharing connection, implying a new strategy to improve the band-gap of birefringent materials.