Intercalates - Exciting Compounds for Solid-State Chemistry Studies

This article describes a laboratory exercise that investigates the incorporation of the guest anion hexacyanoferrate(III) into the layered structure of lithium gibbsite chloride, and its subsequent removal from the lattice with sodium carbonate. X-ray diffraction is used to study the change in interlayer spacing, d upon incorporation of the guest ion into the lithium gibbsite structure. The experiment demonstrates the important relationship between the strength of host–guest interactions, and the size, shape, and particularly charge density of the guest anion. The experiment demonstrates a layer structure that expands upon the incorporation of a guest anion. In this experiment, the large guest hexacyanoferrate(III) anion enters the host lithium gibbsite chloride lattice, displacing the smaller chloride ion and causing an increase in the d spacing. The hexacyanoferrate(III) anion is removed from the lattice by treatment with the high charge density carbonate anion. The incorporation and release of the guest anion is essentially an anion-exchange mechanism, which may be compared and contrasted with other anion exchangers used in chemical practice. Flame atomic absorption spectrometry is used to quantify both the concentration of the guest anion remaining in solution after incorporation and after recovery of the guest ion from the host lattice.