Two polymorphs of bis(2-carbamoylguanidinium) fluorophosphonate dihydrate

Abstract

Two polymorphs of bis(2-carbamoylguanidinium) fluorophosphonate dihydrate, 2C(2)H(7)N(4)O(+)·FO(3)P(2-)·2H(2)O, 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-H···O and N-H···O 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 R(4)(4)(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-H···O 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-H···O and O-H···O hydrogen bonds in (I) are stronger and weaker, respectively, than those in (II). Moreover, in (I), the shortest N-H···O hydrogen bonds are shorter than the shortest O-H···O 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-H···F interactions are far weaker than the N-H···O hydrogen bonds. It follows from the structure analysis that (II) seems to be thermodynamically more stable than (I).