(H3O)Ca2Zn3.5(PO4)4 and Ba2Cd3(PO4)2(HPO4)2: Syntheses, crystal structures and characterizations of two mixed metal phosphates

Two new phosphates, non-centrosymmetric (NCS) (H 3 O)Ca 2 Zn 3.5 (PO 4 ) 4 and centrosymmetric (CS) Ba 2 Cd 3 (PO 4 ) 2 (HPO 4 ) 2 have been prepared by hydrothermal reactions . The single-crystal X-ray structural analyses have shown that they crystallized in space group P −42 1 c and P2 1 /c , respectively·(H 3 O)Ca 2 Zn 3.5 (PO 4 ) 4 features a three-dimensional (3D) network structure composed of ZnO 4 and PO 4 tetrahedra that are interconnected via corner-sharing, forming 1D channels of 6-MRs and 8-MRs which are filled by Ca 2+ and H 3 O + cations, respectively. Ba 2 Cd 3 (PO 4 ) 2 (HPO 4 ) 2 features a layered [Cd 3 (PO 4 ) 2 (HPO 4 ) 2 ] 4- composed of 1D chain of edge-sharing CdO 6 octahedra that are further bridged by PO 4 tetrahedra with Ba 2+ cations filling the interlayer spaces. Luminescent studies suggest that (H 3 O)Ca 2 Zn 3.5 (PO 4 ) 4 emits blue light. Optical diffuse reflectance spectra show the experimental band gaps for (H 3 O)Ca 2 Zn 3.5 (PO 4 ) 4 and Ba 2 Cd 3 (PO 4 ) 2 (HPO 4 ) 2 are 5.67   eV and 5.68   eV, respectively. The UV cut-off edge of title compounds are around at 218   nm·(H 3 O)Ca 2 Zn 3.5 (PO 4 ) 4 exhibits a very weak SHG response.