An investigation of the selectivity behaviour of host compound (R,R)-(−)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol in mixed cresols

Abstract

(R,R)-(−)-2,3-Dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (H2), a tartaric acid-derived host compound, was assessed for its selectivity behaviour in mixed cresols (2Cr, 3Cr and 4Cr) to determine whether, through host–guest chemistry strategies, these isomers may be separated or purified. While each of the isomers was independently included by H2 with 2 : 1 host : guest ratios, significant selectivities were observed for 2Cr when the cresols were mixed equimolarly or in binary and ternary mixtures where guest molar amounts were varied. Therefore, the host selectivity was in the order 2Cr ≫ 4Cr > 3Cr. As examples, 2Cr/4Cr and 2Cr/3Cr equimolar mixtures furnished crystals with as much as 77.6 and 78.5% 2Cr. Thermal analyses showed that the complex stabilities correlated with the host selectivity order: the 2Cr-containing complex was the most stable while 2(H2)·3Cr was the least. SCXRD experiments revealed that the host affinity for 2Cr was as a result of a (guest)O–H⋯π(host) interaction that measured 2.71 Å (H⋯π) (172°); this interaction type was not present in 2(H2)·3Cr or 2(H2)·4Cr. Finally, Hirshfeld surface analyses showed that the C⋯H interactions between host and guest molecules increased in the order 3Cr (23.4%) < 4Cr (26.8%) < 2Cr (29.2%), supportive of the host selectivity order for the cresols.