Journal of Solid State Chemistry 156, 415 } 421 (2001) doi:10.1006/jssc.2000.9016, available online at http://www.idealibrary.com on The Synthesis and Crystal Structures of Two New Hydrated Sodium Monofluorophosphates: NaHPO 3 F ' 2.5 H 2 O (I) and Na 2 PO 3 F ' 10 H 2 O (II) Hillary A. Prescott, Sergei I. Troyanov, and Erhard Kemnitz Humboldt-Universita ( t zu Berlin, Institut fu ( r Chemie, Hessische Str. 1-2, D-10115 Berlin, Germany Received July 5, 2000; in revised form October 18, 2000; accepted October 27, 2000 DEDICATED TO PROFESSOR DR. R. MIETHCHEN ON HIS 60TH BIRTHDAY The structures of two new sodium salts of mono6uorophos- phoric acid, NaHPO 3 F ' 2.5 H 2 O (I) and Na 2 PO 3 F ' 10H 2 O (II), were determined with single-crystal X-ray di4raction at 160 K. I is monoclinic with the space group C2/c, a  19.112(4), b  5.341 (1), c  12.727(3) A s ,   110.18 (3)3, V  1219.4(4) A s 3 , and Z  8( R 1  0.0276 and wR 2 "0.0647). II crystallizes in the monoclinic space group, P 2 1 /c, a  11.380(3), b  10.234(2), c  13.051(4) A s ,   106.49(3)3, V  1457.4(7) A s 3 , and Z  4 (R 1  0.0266 and wR 2  0.0581). The crystal structure of I con- tains hydrogen-bonded zigzag chains of HPO 3 F tetrahedra. The 6uorine atom does not participate in the hydrogen bonding system. In the structure of II, hydrogen bonds create a complex structure of water molecules connected to each other and to the PO 3 F tetrahedron. The structure is isotypic to Na 2 SO 4 ' 10H 2 O with two disordered hydrogen atoms instead of four. The 6uorine atom acts as an acceptor in two of the hydrogen bonds.  2001 Academic Press Key Words: mono6uorophosphate; hydrogen bonding; crystal structure; P+F bond. INTRODUCTION The class of compounds, metal mono#uorophosphates, has been known for about 100 years. The "rst published work discussed a potassium and a rubidium hydrogen mono#uorophosphate (1). The compositions of the com- pounds were determined with chemical analysis, but a con- "rmation of the P}F bond was not possible at that time. Since then, quite a bit of work has been done on mono- #uorophosphates (2). Neels and Grunze reported the synthesis of a sodium and other alkali metal hydrogen mono#uorophosphates (3). The salts were characterized by P and F NMR spectroscopy and Guinier powder di!raction. To whom correspondence should be addressed. Fax: 49-30-2093-7277. E-mail: erhard " kemnitz@chemie.huberlin.de. Mono#uorophosphates are of interest for a structural comparison with the isoelectronic sulfates with emphasis on the hydrogen sulfates. Some hydrogen sulfates are well- known for their phase transitions resulting in high proton conductivity (5), thus leading to the question if the same could be true for the hydrogen mono#uorophosphates. The "rst single-crystal structure was published very recently for cesium hydrogen mono#uorophosphate (4). Interestingly enough, this compound has lattice constants similar to those of a high-temperature phase of cesium hydrogen sulfate (5). In this paper, the structures of both sodium hydrogen mono#uorophosphate 2.5 hydrate (compound I) and disodium mono#uorophosphate decahydrate (compound II) are presented and discussed. The decahydrate is com- pared in detail to the isotypic structure of Glauber's salt, Na  SO  ) 10H  O. EXPERIMENTAL Sample Preparation and Characterization The sodium salt of mono#uorophosphoric acid, NaHPO  F ) 2.5 H  O(I), was prepared in a two-step syn- thesis involving cationic exchange (Amberlite IR 120# , Aldrich) similar to that carried out by Neels and Grunze (3). The eluent (5.0 g, 35 mmol of Na  PO  F in 10 mL water) was passed over a 35-cm column. After complete cationic exchange, sodium carbonate (5.04 g, 48 mmol) was gradually added to the cooled eluate (ice/salt bath) until pH 3.73. The solution was freeze}dried. The raw product was recrys- tallized from aqueous solution by slow evaporation in a desiccator. Weathering was observed in the recrystallized product of I. Some crystals were washed with acetone and a brittle chalk white product was obtained due to dehydration. Crystals of Na  PO  F ) 10H  O(II) were obtained by crystallizing commercial Na  PO  F from aqueous solution 415 0022-4596/01 $35.00 Copyright  2001 by Academic Press All rights of reproduction in any form reserved.