Abstract
myo-Inositol-2,3-D-camphor ketal crystallizes as an incommensurate structure with the C2(0σ2½) 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).
Highlights
Hydrogen bonding is a common source of order–disorder phase transitions, whereby the hydrogen-bonding network is disordered at high temperatures and ordered at low temperatures
Hydrogen bonding has been identified as the main driving force in the order–disorder transition of -[Zn-(pydcH)2]Á3H2O, where pydcH is mono-deprotonated pyridine-2,6-dicarboxylic acid, leading to an incommensurately modulated low-temperature structure (Tabatabaee et al, 2018)
A description of the basic structure will be given, which is the hypothetical three-dimensionally periodic structure that is derived from the modulated structure by ignoring the positional, occupational and atomic displacement parameters (ADPs) modulation functions
Summary
Hydrogen bonding is a common source of order–disorder phase transitions, whereby the hydrogen-bonding network is disordered at high temperatures and ordered at low temperatures. In this special case the group–subgroup relation is of index 1, since the dimensionality of the translation lattice is reduced in the incommensurate phase When these facts are combined, it is unsurprising that ordering of the hydrogen-bonding network has been reported as the crucial feature of numerous incommensurately modulated structures in all classes of compounds from inorganic to organometallic and organic. The hydrogen-bond controlled incommensurately modulated quininium (R)-mandelate features no order– disorder transition (Schonleber & Chapuis, 2004) The crystal structure at 170 K of the enantiomer of 1, myoinositol-1,2-l-camphor ketal [Fig. 1(b)], has previously been described by Gainsford et al (2007) These authors neither report signs of modulation nor a disordered hydrogenbonding network. They do, report a ‘fortuitous’ short contact and the atomic displacement parameters (ADPs) of the hydroxyl O atoms are distinctly enlarged, hinting towards unresolved disorder or overlooked modulation
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