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

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.