Hydrothermal synthesis, structures and optical properties of A2Zn3(SeO3)4·XH2O (A=Li, Na, K; X=2 or 0)

New alkali metal zinc selenites, A 2 Zn 3 (SeO 3 ) 4 · X H 2 O (A=Li, Na, K; X =2 or 0) were prepared through hydrothermal reactions . Li 2 Zn 3 (SeO 3 ) 4 ·2H 2 O ( 1 ) crystallizes in the monoclinic space group P 2 1 / c with lattice parameters a =8.123(4), b =9.139(4), c =7.938(3)   Å, β =112.838(9)°. Na 2 Zn 3 (SeO 3 ) 4 ·2H 2 O ( 2 ) crystallizes in the monoclinic space group C2/c with lattice parameters a =15.7940(18), b =6.5744(8), c =14.6787(17) Å, β =107.396(3)°. K 2 Zn 3 (SeO 3 ) 4 ( 3 ) crystallizes in the monoclinic space group C2/c with lattice parameters a =11.3584(12), b =8.6091(9), c =13.6816(14)   Å, β =93.456(2)°. The anionic structures are composed of [Zn 3 O 12 ] 18− sheets, chains, and “isolated” units in compound 1, 2, 3, respectively, and trigonal pyramids SeO 3 2− . The compounds were characterized by the solid state UV–vis–NIR diffuse reflectance spectroscopy , infrared spectra and thermogravimetric analysis .