New Selenites:  Syntheses, Structures, and Characterization of Centrosymmetric Al₂(Se₂O₅)₃ and Ga₂(Se₂O₅)₃ and Non-centrosymmetric In₂(Se₂O₅)₃

The syntheses, structures, and characterization of three new mixed metal selenites, Al 2 (Se 2 O 5 ) 3, Ga 2 (Se 2 O 5 ) 3, and In 2 (Se 2 O 5 ) 3 are reported. Al 2 (Se 2 O 5 ) 3 and Ga 2 (Se 2 O 5 ) 3 are isostructural to Cr 2 (Se 2 O 5 ) 3 and crystallize in the monoclinic space group P 2 1 / n (No. 14) with a = 10.825(6) Å, b = 11.214(3) Å, c = 11.567(6) Å, and β = 94.92(3)° for Al 2 (Se 2 O 5 ) 3 and a = 10.901(6) Å, b = 11.367(3) Å, c = 11.682(3) Å, and β = 95.07(3)° for Ga 2 (Se 2 O 5 ) 3 . The third material, In 2 (Se 2 O 5 ) 3, crystallizes in the non-centrosymmetric space group Pc (No. 7) with a = 11.1463(5) Å, b = 13.3210(6) Å, c = 9.7149(4) Å, β = 105.478(1)°, and Z = 4. Nonlinear optical measurements on In 2 (Se 2 O 5 ) 3 indicate the material has second harmonic generating properties, with an efficiency of approximately 10 times SiO 2 . Infrared and thermogravimetric analyses for all three compounds are also presented.