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/H 2 O/H 3 PO 4 /HF/guanidine or NH 4 F (180 °C, autogenous pressure, 4 days). The structures of both compounds have been characterized by single-crystal X-ray diffraction. The (NH 4 )GaPO 4 F phase is isostructural with the KTiOPO 4 (KTP) structural type. The structure of the second phase (NH4)2Ga2(PO 4 )(HPO 4 )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 PO 4 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 19 F and 31 P solid-state nuclear magnetic resonance spectroscopy using high-speed MAS experiments (30 kHz). 19 F NMR indicates a full occupancy by fluorine for the atomic sites bridging the gallium atoms, Crystal data for (NH 4 )GaPO 4 F: orthorhombic, space group Pna2 1 (no. 33), a = 12.9207(2) A, b = 6.440(1) A, c = 10.4147(2) A, V = 866.60(3) A 3 , Z = 8, R1 = 0.0279%, wR2 = 0.0785 for 2216 reflections with I > 2σ(I). Crystal data for (NH4) 2 Ga 2 (P04)(HP04)F 3 : orthorhombic, space group Pna2 1 (no. 33), a = 12.4967(2) A, b = 7.7015(1) A, c = 9.8463(1) A, V = 947.67(2) A 3 , Z = 4, R1 = 0.0406, wR2 = 0.0985 for 2820 reflections with I > 2σ(I).