Tripod molecules build molecular networks and open-dimer capsules by weak interactions

Abstract

Three tripod molecules, tris(2-methoxy-5-nitrobenzyl)phosphine oxide (1), tris(2-butoxy-3-methyl-5-nitrobenzyl)phosphine oxide (2), and tris(3-nitrobenzyl)amine (TNBA), were synthesized and crystallized. The structures of 1, 2, and their comparison (TNBA) were determined by X-ray crystallography. It is noteworthy that compound 1 interacted with adjacent molecules via - stacking and CH··· interactions to yield an open supramolecular network with the porosity P in 8.9%, whereas compound 2 gathered closely to form an open-dimer capsule by sixfold NO··· and triple CH···O interactions, which showed a rare example of a stable in, out-invertomer of phosphine inversion existing in open-dimers. A series of columns were built and arranged side by side by these weak interactions. By contrast, TNBA crystallized to form a 2D network maintained by CH···O and CH··· interactions. It seems minor changes of the chemical structure may cause large differences in the crystal structure and interactions in crystal engineering. tripod molecule, supramolecular network, open-dimer capsule, weak interaction