(H 3 O)Ca 2 Zn 3.5 (PO 4 ) 4 and Ba 2 Cd 3 (PO 4 ) 2 (HPO 4 ) 2 : Syntheses, crystal structures and characterizations of two mixed metal phosphates

Novel antimony phosphates with enlarged birefringence induced by lone pair cations

Phosphates, whose obvious disadvantage is the relatively small birefringence, can be overcome by the introduction of post-transition metal cations containing stereochemically active lone-pair electrons. In this paper, two new compounds were successfully explored in the A-Sb-P-O system, i.e. Cs2Sb3O(PO4)3 (CsSbPO) and (NH4)2Sb4O2(H2O)(PO4)2[PO3(OH)]2 (NH4SbPOH). Transmission spectra show that CsSbPO has a surprising transmission range with a UV cutoff edge of 213 nm. First-principles calculations show that both compounds have a wide band gap (5.02 eV for CsSbPO and 5.30 eV for NH4SbPOH) and enlarged birefringence (Δn = 0.034@1064 nm for CsSbPO and Δn = 0.045@1064 nm for NH4SbPOH). The results of real-space atom-cutting investigations show that the distorted [SbOx] polyhedra originating from the asymmetric lone pair electrons give the main contribution to the total birefringence and overcome the disadvantage of small birefringence of phosphates but maintain wide transition windows.

Syntheses, crystal structures and optical properties of two one-dimensional germanophosphates: HRb3Ge2(HPO4)6 and CsGe(HPO4)2(OH)

Germanophosphates, as a young class of metal phosphates, have been less reported but might possess more diverse structural types and potential applications. Here, two one-dimensional (1D) alkali-metal germanophosphates (GePOs), namely, hydrogen hexakis(μ-hydrogen phosphato)digermaniumtrirubidium, HRb₃Ge₂(HPO₄)₆ (1), and caesium bis(μ-hydrogen phosphato)(μ-hydroxido)germanium, CsGe(HPO₄)₂(OH) (2), have been prepared by the solvothermal method. Compound 1 shows 1D [Ge(HPO₄)₆]_∞ chains along the c axis formed by GeO₆ octahedra and PO₄ tetrahedra, with Rb⁺ cations dissociated between the chains. Compound 2 also exhibits 1D [Ge(HPO₄)₄(OH)₂]_∞ chains constructed from adjacent Ge(HPO₄)₄(OH)₂ octahedra, with Cs⁺ cations dissociated between the chains. XRD, TGA, IR and UV-Vis-NIR absorption spectra are presented and discussed for both compounds.