Abstract
During a systematic study of monofluorophosphates, i.e., compounds comprising the tetrahedral anion PO3F2−, twelve, for the most part new, compounds were obtained from aqueous solutions. Crystal structure refinements based on single crystal X-ray diffraction data revealed the previously unknown crystal structures of CdPO3F(H2O)2, Cr2(PO3F)3(H2O)18.8, Pb2(PO3F)Cl2(H2O), (NH4)2M(PO3F)2(H2O)2 (M = Mg, Mn, Co), NH4Cr(PO3F)2(H2O)6, NH4Cu2(H3O2)(PO3F)2, (NH4)2Zn(PO3F)2(H2O)0.2, and (NH4)2Zn3(PO3F)4(H2O), as well as redeterminations of ZnPO3F(H2O)2.5 and (NH4)2Ni(PO3F)2(H2O)6. From the previously unknown crystal structures, CdPO3F(H2O)2 (space group P1¯), Cr2(PO3F)3(H2O)18.8 (P1¯), Pb2(PO3F)Cl2(H2O) (Pnma), NH4Cr(PO3F)2(H2O)6 (R3¯m), (NH4)2Zn(PO3F)2(H2O)0.2 (C2/c), and (NH4)2Zn3(PO3F)4(H2O) (I4¯3d) each crystallizes in an unique crystal structure, whereas compounds (NH4)2M(PO3F)2(H2O)2 (M = Mg, Co) crystallize in the (NH4)2Cu(PO3F)2(H2O)2 type of structure (C2/m) and (NH4)2Mn(PO3F)2(H2O)2 in a subgroup thereof (P21/n, with a klassengleiche relationship of index 2), and NH4Cu2(H3O2)(PO3F)2 (C2/m) crystallizes isotypically with natrochalcite-type KCu2(H3O2)(SO4)2. A survey on the PO3F2− anion, including database entries of all inorganic compounds comprising this group, revealed mean bond lengths of P–O = 1.506(13) Å, P–F = 1.578(20) Å, and angles of O–P–O = 113.7(1.7)° and O–P–F = 104.8(1.7)°, using a dataset of 88 independent PO3F2− anions or entities. For those crystal structures of monofluorophosphates where hydrogen bonding is present, in the vast majority of cases, hydrogen bonds of the type D–H···F–P (D = O, N) are not developed.
Highlights
The family of monofluorophosphates comprising the PO3 F2− anion was introduced by Lange more than 90 years ago [1]
For syntheses of NH4 + -containing monofluorophosphates, the starting compound (NH4 )2 PO3 F(H2 O) was prepared according to Schülke and Kayser [11] and its purity checked with X-ray powder diffraction (XRPD)
Single crystals of twelve and partly unknown monofluorophosphate phases were grown from aqueous solutions
Summary
The family of monofluorophosphates comprising the PO3 F2− anion was introduced by Lange more than 90 years ago [1]. PO4 3− and F− anions are sometimes incorrectly described as “fluorophosphates”, e.g., Mn2 PO4 F [2] or Na2 FePO4 F [3]. These compounds correctly belong to the family of ‘phosphate fluorides’. Various preparation methods for monofluorophosphates as well as applications of this family of compounds as additives in toothpastes, wood preservatives, corrosion inhibitors, solubility inhibitors for lead in potable water sources, or as active agents against osteoporosis or caries during biomineralization of fluoroapatite were summarized some time ago [4]. Some monofluorophosphates were shown to exhibit excellent nonlinear optical (NLO) behaviour [5]
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