Comparative Structural Studies of Four Homologous Thioamidic Unclosed Crytpands: Self-Encapsulation of Lariat Arm, Odd–Even Effects, Anomalously Short S···S Chalcogen Bonding, and More

Abstract

Unclosed cryptands (UCs) 4a–d containing flexible (CH2)n spacers (n = 2–5) and a fixed p-nitrophenyl thioamide substituent (lariat arm) were synthesized and characterized by single crystal X-ray analysis. Comparative analysis of their crystal structures provided an opportunity to recognize that conformation of 4a–d and occurrence of lattice solvent strictly depend on the length and parity of aliphatic linkers. Namely, the degree of self-inclusion of the lariat arm within the macrocyclic cavity was found to increase with greater elongation of the CH2 spacer. Odd-membered UCs (4b and 4d) showed a tendency to crystallize without lattice solvent, while even-membered UCs (4a and 4c) crystallized as various solvates. For two solvates of UC 4c anomalously short and highly directional C═S···S═C chalcogen interactions (dS···S = 3.21–3.35 A) were observed between adjacent UC molecules, forming a dimeric cube-like supramolecular assembly. Packing of dimers and the length of homo-chalcogen interaction were affected b...