Crystal Structure of Tetrapentylammonium Chloride Complex with Rac-1,1′-Bi-2-naphthol: The Effect of Solvent and Counter Anion on Biradial Conformation of the Surfactant Molecule

Abstract

Supramolecular chemistry applies molecular-recognition processes, rest heavily on understanding the recognition properties of the functional groups involved in these interactions, i.e. on molecular information stored in the interacting species. It aims to construct highly complex, functional chemical systems from components held together by intermolecular interactions. Various supramolecular interactions are used as tools in crystal engineering in order to develop novel functional materials.1 Recently, in addition to the well developed molecular interactions and conformational studies on N-alkylammonium halides (mono, di, tri-alkylammonium halides) complexes with nonplanar aromatic molecules in respect to knowing the inter, and intra-molecular interactions and preferred conformation exhibited by both the non-planar aromatic molecule and the alkyl chain, much interest has been shown by various researchers due to its useful applications in separation science and crystal engineering.2,3 Our group of researchers have been recently involved in examining the preferential conformation of non-planar aromatic molecules and the alkyl chain in crystal complexes involving tetra-n-alkylammonium halides (n = 4, 5,···) with non-planar aromatic molecules in order to exploit probable conformational adjustments that could occur due to effect of increases in chain length and changes of the counter anion in the hydrogen-bonded binaphthol cavity environ. It has been shown by our group that crystal complexes of tetrabutylammonium halides (R4N·X, where R = butyl, and X = Br or Cl, hereafter TBAB, or TBAC, respectively) with rac-1,1′-bi-2-naphthol (hereafter, BNP) are isomorphous.4 In both crystal structures (TBAB/BNP and TBAC/BNP) the alkyl chains exhibit conformational and orientational disordered structures, while in a tetrapentylammonium bromide (R = pentyl, hereafter, TPAB) complex with BNP (hereafter, TPAB/BNP), the biradial conformation is exhibited by the alkyl chains.5 Per this knowledge we were challenged to investigate how changes of the counter anion from Br– to Cl– as well as an increase in the alkyl chain from n = 4 to 5 can also generate any conformational adjustments in both the binaphthol molecules or the alkyl chains. Interestingly, in an attempt to obtain a TPAC/BNP crystal complex, the crystal complex entrapped solvent (acetonitrile) molecules, as per revealed by X-ray crystallography studies. Thus, in this manuscript we discuss the findings revealed in its crystal structure studies. Crystals suitable for X-ray diffraction studies were obtained within seven days by the slow evaporation of a 2021 © The Japan Society for Analytical Chemistry