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Isomeric Ionic Lithium Isonicotinate Three-Dimensional Networks and Single-Crystal-to-Single-Crystal Rearrangements Generating Microporous Materials

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posted on 19.05.2014, 00:00 by Brendan F. Abrahams, A. David Dharma, Martin J. Grannas, Timothy A. Hudson, Helen E. Maynard-Casely, Graham R. Oliver, Richard Robson, Keith F. White
Reaction between LiOH and isonicotinic acid (inicH) in the appropriate solvent or mixture of solvents affords a family of variously solvated forms of a simple ionic lithium salt, viz., Li+inic·S (where S = 0.5 morpholine, 0.5 dioxane, 0.25 n-hexanol, 0.5 N-methylpyrrolidinone, 0.5 N,N-dimethylformamide, 0.5 n-propanol, 0.5 cyclohexanol, 0.5 pyridine, 0.5 t-butanol, 0.5 ethanol, and 0.5 methanol). Three-dimensional Li+inic frameworks containing solvent-filled channels are present in all of these except for the MeOH and EtOH solvates. The nondirectional character of the electrostatic interactions between the Li+ and inic ions bestows an element of “plasticity” upon the framework, manifested in the observation of no less than five different framework structures within the family. Unusual single-crystal-to-single-crystal transformations accompany desolvation of Li+inic·S in which the Li+inic framework undergoes a major rearrangement (from a structure containing “8484 chains” to one with “6666 chains”). The “before and after” structures are strongly suggestive of the mechanism and the driving force for these solid state framework rearrangements: processes which further demonstrate the “plasticity” of the ionic Li­(inic) framework. A solid-state mechanism for these desolvation processes that accounts very satisfactorily for the formation of the channels and for the diverse geometrical/topological aspects of the transformation is proposed. The reverse process allows the regeneration of the solvated 8484 form. When the 6666 Li+inic form is immersed in carbon disulfide, a single-crystal-to-single-crystal transformation occurs to generate Li+inic·0.25CS2. The hydrate, Li+inic·2H2O which consists of discrete Li­(inic)·H2O chains obtained by recrystallizing the salt from water, can also be obtained by hydration of the 6666 form. A dense 3D network with the formula, Li­(inic) can be obtained in a reversible process by the removal of the water from the hydrated form and also by crystallization from a t-amyl alcohol solution.

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