Crystal structures of two formamidinium hexa-fluorido-phosphate salts, one with batch-dependent disorder.

Syntheses of the acyclic amidinium salts, morpholino-formamidinium hexa-fluorido-phosphate [OC 4 H 8 N-CH=NH 2 ]PF 6 or C 5 H 11 N 2 O + ·PF 6 - , 1 , and pyrrolidinoformamidinium hexa-fluorido-phosphate [C 4 H 8 N-CH= NH 2 ]PF 6 or C 5 H 11 N 2 + ·PF 6 - , 2 , were carried out by heating either morpholine or pyrrolidine with triethyl orthoformate and ammonium hexa-fluorido-phosphate. Crystals of 1 obtained directly from the reaction mixture contain one cation and one anion in the asymmetric unit. The structure involves cations linked in chains parallel to the b axis by N-H⋯O hydrogen bonds in space group Pbca , with glide-related chains pointing in opposite directions. Crystals of 1 obtained by recrystallization from ethanol, however, showed a similar unit cell and the same basic structure, but unexpectedly, there was positional disorder [occupancy ratio 0.639 (4):0.361 (4)] in one of the cation chains, which lowered the crystal symmetry to the non-centrosymmetric space group Pca2 1 , with two cations and anions in the asymmetric unit. In the pyrrolidino compound, 2 , cations and anions are ordered and are stacked separately, with zigzag N-H⋯F hydrogen-bonding between stacks, forming ribbons parallel to (101), extended along the b -axis direction. Slight differences in the delocalized C=N distances between the two cations may reflect the inductive effect of the oxygen atom in the morpholino compound.