Acta Cryst. (2012). C68, o71-o75 [ doi:10.1107/S0108270111053133 ]
Abstract: Two polymorphs of bis(2-carbamoylguanidinium) fluorophosphonate dihydrate, 2C2H7N4O+·FO3P2-·2H2O, are presented. Polymorph (I), crystallizing in the space group Pnma, is slightly less densely packed than polymorph (II), which crystallizes in Pbca. In (I), the fluorophosphonate anion is situated on a crystallographic mirror plane and the O atom of the water molecule is disordered over two positions, in contrast with its H atoms. The hydrogen-bond patterns in both polymorphs share similar features. There are O-HO and N-HO hydrogen bonds in both structures. The water molecules donate their H atoms to the O atoms of the fluorophosphonates exclusively. The water molecules and the fluorophosphonates participate in the formation of R44(10) graph-set motifs. These motifs extend along the a axis in each structure. The water molecules are also acceptors of either one [in (I) and (II)] or two [in (II)] N-HO hydrogen bonds. The water molecules are significant building elements in the formation of a three-dimensional hydrogen-bond network in both structures. Despite these similarities, there are substantial differences between the hydrogen-bond networks of (I) and (II). The N-HO and O-HO hydrogen bonds in (I) are stronger and weaker, respectively, than those in (II). Moreover, in (I), the shortest N-HO hydrogen bonds are shorter than the shortest O-HO hydrogen bonds, which is an unusual feature. The properties of the hydrogen-bond network in (II) can be related to an unusually long P-O bond length for an unhydrogenated fluorophosphonate anion that is present in this structure. In both structures, the N-HF interactions are far weaker than the N-HO hydrogen bonds. It follows from the structure analysis that (II) seems to be thermodynamically more stable than (I).
Formula: Two polymorphs of 2C2H7N4O+·FO3P2-·2H2O
Structure factor file (CIF format) (64.4 kbytes)
Structure factor file (CIF format) (106.7 kbytes)
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