4-Carboxypyridinium perchlorate 18-crown-6 dihydrate clathrate and 4-carboxypyridinium tetrafluoroborate 18-crown-6 dihydrate clathrate

Abstract

Mixtures of 4-carboxypyridinium perchlorate or 4-carboxypyridinium tetrafluoroborate and 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) in ethanol and water solution yielded the title supramolecular salts, C(6)H(6)NO(2)(+)·ClO(4)(-)·C(12)H(24)O(6)·2H(2)O and C(6)H(6)NO(2)(+)·BF(4)(-)·C(12)H(24)O(6)·2H(2)O. Based on their similar crystal symmetries, unit cells and supramolecular assemblies, the salts are essentially isostructural. The asymmetric unit in each structure includes one protonated isonicotinic acid cation and one crown ether molecule, which together give a [(C(6)H(6)NO(2))(18-crown-6)](+) supramolecular cation. N-H···O hydrogen bonds between the protonated N atoms and a single O atom of each crown ether result in the 4-carboxypyridinium cations `perching' on the 18-crown-6 molecules. Further hydrogen-bonding interactions involving the supramolecular cation and both water molecules form a one-dimensional zigzag chain that propagates along the crystallographic c direction. O-H···O or O-H···F hydrogen bonds between one of the water molecules and the anions fix the anion positions as pendant upon this chain, without further increasing the dimensionality of the supramolecular network.

HUG and SQUEEZE: using CRYSTALS to incorporate resonant scattering in the SQUEEZE structure-factor contributions to determine absolute structure

“…The agreement can be visualized in plots of D hug versus D atom . Table 1 lists solvated structures selected from the recent literature where the molecules of interest contained only light atoms and the solvents were reasonably well defined: sgd240 (Chernega et al, 2009), fg3257 (Bojarska et al, 2012), ky3014 (Shi et al, 2012), sgd464 (Davies et al, 2013a), sgd475 (Davies et al, 2013b), sk3422 (Fá bry et al, 2012) and awisac02 (Qian et al, 2016). The absolute structures were confirmed by rerefining the atomic model in CRYSTALS.…”