The role of hydrogen bonding in the incommensurate modulation of myo-inositol camphor ketal

Abstract

myo-Inositol-2,3-d-camphor ketal crystallizes as an incommensurate structure with the C2(0σ₂1/2) superspace group symmetry [σ₂ = 0.1486 (3) at 100 K]. The bornane and myo-inositol moieties aggregate in distinct layers extending parallel to (001). The myo-inositol rings are connected by a complex hydrogen-bonding network extending in two dimensions, which is disordered in the basic structure and (mostly) ordered in the actual modulated structure. The domains of definition of the H atoms in internal space were derived by chemical reasoning and modeled with crenel functions. By tracing the hydrogen bonding, distinct chains, which are periodic in the [100] direction, are identified. These chains possess one of two possible orientations with respect to the hydrogen bonding. The incommensurate modulation is characterized by a non-periodic succession of the two chain orientations in the [010] direction. On heating, the σ₂-component of the modulation wave vector decreases from σ₂ = 0.1486 (3) at 100 K to σ₂ = 0.1405 (6) at 430 K, which means that the periodicity of the modulation wave increases. No order-disorder phase transition was evidenced up to the melting point (with decomposition).