BaSb(PO) and CdSb(PO)(HO): Two New Antimonous Phosphates with Distinct [Sb(PO)] Structure Types and Enhanced Birefringence.

Two new antimonous phosphates, namely BaSb(PO) and CdSb(PO)(HO), have been successfully prepared through mild hydrothermal reactions. BaSb(PO) features a 1D [Sb(PO)] chain structure separated by Ba cations while CdSb(PO)(HO) presents a 2D [Sb(PO)] layered structure with Cd located at the interlayer space. The [Sb(PO)] chain in BaSb(PO) is the first example of 1D antimonous phosphate structure, and CdSb(PO)(HO) represents the first d transition metal antimonous phosphate. Based on UV-vis-NIR spectra, both BaSb(PO) and CdSb(PO)(HO) can display large optical band gaps (4.30 and 4.36 eV, respectively). But their transparent ranges are quite different because of the coordination water of CdSb(PO)(HO) (500-2000 and 500-1300 nm for Ba and Cd compounds). The anhydrous BaSb(PO) shows high thermal stability in the nitrogen atmosphere (900 °C). Because of the incorporation of the lone pair cation of Sb(III), the birefringence of BaSb(PO) and CdSb(PO)(HO) has been enhanced to 0.086 and 0.053 at 532 nm, respectively.