Supramolecular structures containing ‘isolated’ pentaborate anions and non-metal cations: Crystal structures of [Me3NCH2CH2OH][B5O6(OH)4] and [4-MepyH, 4-Mepy][B5O6(OH)4]

The solid-state structures of two non-metal pentaborates [Me3NCH2CH2OH][B5O6(OH)4] (1) and [4-MepyH, 4-Mepy][B5O6(OH)4] (2) have been determined by single-crystal X-ray diffraction methods. Structures 1 and 2 both contain supramolecular pentaborate frameworks held together by extensive H-bond interactions. The framework of 1 exists essentially as planes of pentaborate anions linked via three pairwise ‘planar’ β → α interactions, with a fourth β → β interaction crosslinking the planes. The framework of 2 is very similar except that one of the three pairwise linkages within the plane is replaced by pairwise ‘step-like’ bifurcated H-bonds to both α sites of a neighboring anion. The cations in 1 and the cations and neutral 4-Mepy ligands in 2 are present in the framework cavities and channels, with additional H-bond interactions existing between cations and anions.

A pairwise ‘step-like’ bifurcated H-bond interaction is observed (right) in the supramolecular pentaborate framework of [4-MepyH, 4-Mepy][B5O6(OH)4] in addition to the more commonly observed pairwise ‘planar’ H-bond interactions (left).Figure optionsDownload as PowerPoint slide