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.