Two Indium Iodate-Nitrates with Large Birefringence Induced by Hybrid Anionic Functional Groups and Their Favorable Arrangements.

Two new indium iodate-nitrates, In(IO 3 ) 2 (NO 3 ) ( 1 ) and [In(IO 3 )(OH)(H 2 O)](NO 3 ) ( 2 ), were rationally designed through the integration of hybrid anionic functional units. They exhibit large birefringences ( 1 , 0.269; 2 , 0.188, at 532 nm) and wide band gaps ( 1 , 4.08 eV; 2 , 4.39 eV), which is attributed to the synergistic effect of two types of birefringence-active units, namely, lone-pair IO 3 and π-conjugated NO 3 anionic groups. Through the substitution of OH and H 2 O of 2 with IO 3 , the hydrogen bonds of 2 are eliminated and the birefringence of 1 is greatly enhanced, highlighting the intriguing role of isovalent substitution in the discovery of fascinating optical materials.