Hydrothermal synthesis and structural characterization of (NH4)GaPO4F, KTP-type and (NH4)2Ga2(PO4) (HPO4)F3, pseudo-KTP-type materials

Two new fluorinated gallium phosphates have been hydrothermally synthesized in the system GaOOH/H2O/H3PO4/HF/guanidine or NH4F (180 degrees C, autogenous pressure, 4 days). The structures of both compounds have been characterized by single-crystal X-ray diffraction. The (NH4)GaPO4F phase is isostructural with the KTiOPO4 (KTP) structural type. The structure of the second phase (NH4)(2)Ga-2(PO4)(HPO4)F-3, named pseudo-KTP or p-KTP, is closely related to that of KTP. In the latter, the existence of terminal P-OH and Ga-F bond along the b axis prevents the full connection by corner-sharing of the PO4 and Ga(O,F)(6) units as it occurs in KTP structure. It results in a more distorted framework in which the occluded ammonium cations interact mainly with the P-OH and Ga-F terminal bonds. The structure of p-KTP was examined by F-19 and P-31 solid-state nuclear magnetic resonance spectroscopy using high-speed MAS experiments (30 kHz). F-19 NMR indicates a full occupancy by fluorine for the atomic sites bridging the gallium atoms. Crystal data for (NH4)GaPO4F: orthorhombic, space group Pna2(1) (no. 33), a = 12.9207(2) Angstrom, b = 6.440(1) Angstrom, c = 10.4147(2) Angstrom, V = 866.60(3) Angstrom(3), Z = 8, R1 = 0.0279%, wR2 = 0.0785 for 2216 reflections with I > 2 sigma(I). Crystal data for (NH4)(2)Ga-2(PO4)(HPO4)F-3 : orthorhombic, space group Pna2(1) (no. 33), a = 12.4967(2) Angstrom, b = 7.7015(1) Angstrom, c = 9.8463(1) Angstrom, V = 947.67(2) Angstrom(3), Z = 4, R1 = 0.0406, wR2 = 0.0985 for 2820 reflections with I > 2 sigma(I).