[M(OH)2]3(IO3)(SeO4)·H2O (M = Ga and In): metal iodate–selenate nonlinear optical materials with a hexagonal tungsten oxide-type topology

Exploration of new iodates is crucial due to their splendid applications in the nonlinear optical (NLO) field. Two new IIIA metal iodate–selenates, namely, [M(OH)2]3(IO3)(SeO4)·H2O (M = Ga and In), have been successfully synthesized using the hexagonal tungsten oxide (HTO) framework as an ideal structural template. Isostructural [M(OH)2]3(IO3)(SeO4)·H2O (M = Ga and In) crystallize in the polar space group P63mc. Their structures feature ∞[MO2(OH)2]3− (M = Ga, In) layers composed of corner-shared circular M3O6(OH)9 trimeric units based on MO2(OH)4 octahedra. The SeO4 groups are capped above half of the trimeric units of the layers while the IO3 groups are capped below the remaining trimeric units of the layers. Both compounds exhibit moderate phase-matchable second-harmonic generation (SHG) responses (2.9× and 3.8× KH2PO4) under 1064 nm laser radiation and the same band gap of 3.38 eV. Results of theoretical calculations revealed that their SHG effects originated from the synergistic effect of MO6, IO3 and SeO4 groups. So far reports on iodate–selenates are scarce and this work provides a new perspective to design new NLO materials through polar HTO-type topologies and a mixed-anionic strategy.