The Crystal Structure of a Benzyltriethylammonium Bromide Complex with rac-1,1′-Binaphthalene-2,2′-diol: The Inclusion of an Arylammonium Salt by an Assembly of Binaphthol Groups

Abstract

The concepts of crystal engineering and molecular recognition are exceedingly similar; both fields are concerned with the manipulation of intermolecular interactions in the architecture of supramolecular assemblies. In such studies, both strong and weak interactions are considered both independently and jointly concerning the molecular design strategy.1 Recently, many efforts have been focused on controlling H-bonds in supramolecular and crystal structures of complexes involving phenol derivatives and quaternary alkyl ammonium salts to achieve molecular recognition phenomena.2 This knowledge has had pharmaceutical significance, as well as applications in separation science and biomembrane studies.3 Our search of the Cambridge Structure Database Ver. 5.34, 2013, recently revealed to us that no studies have been conducted concerning molecular recognition between a quaternary arylammonium halide and a phenol derivative since such a study could reveal the suitability of quaternary arylammonium halides that bind with phenol derivatives, as observed in quaternary alkylammonium halides, as well as to employ this knowledge into crystal engineering and supramolecular studies. Gratifingly, our group found that benzyltrimethylammonium chloride, (hereafter, BTMAC) binds with rac-1,1′-binaphthalene-2,2′-diol (hereafter, BNP) to form BTMAC/BNP complex4 in a molecular recognition phenomenom. This revealed how the benzyl group influences a crystal packing mode favorable for the generation of C–H···π, C–H···O, and O–H···Cl intermolecular interactions, and indicating the relevance of these kind of weak H–bonds (C–H···π, C–H···O) in the binding phenomena. Thus, we also found it is important to investigate the binding phenomena between benzyltriethylammonium bromide (hereafter, BTEAB) and BNP through crystal structure studies in order to understand how alteration of the halide anion from Cl– to Br–, as well as to change in the trialkyl group from trimethyl to triethyl group on the ammonium cation could also enhance similar crystal packing modes and weak interactions through the influence of the benzyl group or not. Thus, the revelations from the crystal structure studies of BTEAB/BNP complex are discussed in this manuscript. Suitable crystals for X-ray diffraction studies were obtained within 8 days by slow evaporation of a warmed acetone/ ethylacetate (20 mL) mixture in which BTEAB (0.27 g, 1 mmol), and BNP (0.29 g, 1 mmol) were dissolved. Crystal 2021 © The Japan Society for Analytical Chemistry