Structure and magnetism of a verdazyl radical clathrate hydrate. Strong intermolecular magnetic interactions derived from π-stacking within ice-like channels

Abstract

Deprotonation of 1,5-dimethyl-6-oxoverdazyl-3-carboxylic acid (2H) in acetonitrile/water affords crystals of the sodium salt of the carboxylate radial anion as a hydrated material (3). The solid state structure of 3 consists of a 2-D array of antiparallel stacked verdazyl carboxylate radical anions (2-) pillared between chains of sodium cations. These layers are separated by structurally ordered water layers. These layers consist of fused polygons based on OH⋯O hydrogen bonds that assemble into a complex 2-D hydrogen bonded network. The alternating layers are also linked via an orthogonal hydrogen bonded network. The overall structure resembles a 2-D ionic clathrate hydrate with radical stacks contained within channels. Analysis of temperature dependent magnetic susceptibility measurements reveal very strong antiferromagnetic exchange interactions (J = −290 cm⁻¹) which can be ascribed to the 1-D stacks of radicals within the hydrate structure.