Li+ and Ca2+ Derivatives of the Isonicotinate-N-oxide Ion Including Single Crystal-to-Single Crystal Transformations

Abstract

Crystals of [Li(inox)(H2O)] (where inox– = the isonicotinate-N-oxide ion) are obtained from aqueous solution. The Li+ cations and the carboxylate anions form a two-dimensional (2D) sheet containing four-membered (−Li–O–Li–O−) rings and 16-membered (−Li–O–C–O−)4 rings; the sheets are linked to adjacent parallel sheets through hydrogen bonds. Crystals of solvent-free [Li(inox)], obtained from t-butanol, consist of a three-dimensional network which can also be prepared in microcrystalline form by dehydration of [Li(inox)(H2O)] at 200 °C. Crystals of [Ca(inox)2(H2O)2] contain 2D sheets with 4,4 topology in which Ca2+ ions, bound by trans water molecules, provide the 4-connecting nodes. The Ca(H2O)22+ units are linked by carboxylate groups to generate 16-membered (−Ca–O–C–O−)4 rings. Sheets are bound together by hydrogen bonds between the pyridine-N-oxide units and coordinated water molecules. [Ca(inox)2(H2O)2] can be dehydrated at 190 °C in a single crystal-to-single crystal transformation to give [Ca(inox)2] whose structure is related to that of the hydrated precursor. A proposed solid-state mechanism for this single crystal-to-single crystal transformation, in which the N-oxide takes up the site on calcium vacated by water is proposed.