Mixed crystals of 2-carbamoylguanidinium with hydrogen fluorophosphonate and hydrogen phosphite in the ratios 1:0, 0.76 (2):0.24 (2) and 0.115 (7):0.885 (7).

The title compounds, 2-carbamoylguanidinium hydrogen fluorophosphonate, C(2)H(7)N(4)O(+)·HFO(3)P(-), (I), 2-carbamoylguanidinium-hydrogen fluorophosphonate-hydrogen phosphite (1/0.76/0.24), C(2)H(7)N(4)O(+)·0.76HFO(3)P(-)·0.24H(2)O(3)P(-), (II), and 2-carbamoylguanidinium-hydrogen fluorophosphonate-hydrogen phosphite (1/0.115/0.885), C(2)H(7)N(4)O(+)·0.115HFO(3)P(-)·0.885H(2)O(3)P(-), (III), are isostructural with guanylurea hydrogen phosphite, C(2)H(7)N(4)O(+)·H(2)O(3)P(-) [Fridrichová, Němec, Císařová & Němec (2010). CrystEngComm, 12, 2054-2056]. They constitute structures where the hydrogen phosphite anion has been fully or partially replaced by hydrogen fluorophosphonate. The title structures are the fourth example of isostructural compounds which differ by the presence of hydrogen fluorophosphonate and hydrogen phosphite or fluorophosphonate and phosphite anions. Moreover, the present study reports structures with these mixed anions for the first time. In the reported mixed salts, the P and O atoms of either anion overlap almost exactly, as can be judged by comparison of their equivalent isotropic displacement parameters, while the P-F and P-H directions are almost parallel. There are strong O-H···O hydrogen bonds between the anions, as well as strong N-H···O hydrogen bonds between the 2-carbamoylguanidinium cations in the title structures. Altogether they form a three-dimensional hydrogen-bond pattern. Interestingly, rare N-H···F interactions are also present in the title structures. Another exceptional feature concerns the P-O(H) distances, which are about as long as the P-F distance. The dependence of P-F distances on the longest P-O distances in FO(3)P(2-) or HFO(3)P(-) is presented. The greater content of hydrogen phosphite in the mixed crystals causes a larger deformation of the cations from planarity.