Jozef Hodyl PhD Thesis - Theses - Flinders University

A1 3542Neutral GuestBAnionic GuestHostCHost-GuestDFigure 6.713 C CPMAS NMR spectra for (A) 2,6-dihydroxybenzoic acid (B) sodium 2,6-dihydroxybenzoate, (C) Si-GPS-[Cd(Trac)](ClO 4 ) 2 and (D) Si-GPS-[Cd(Trac)(2,6-dihydroxybenzoate)](ClO 4 ). All spectra are shown with line broadening.This arises because hydroxybenzoates are able to hydrogen bond across theircarboxy as well as their hydroxy termini, both intramolecularly and intermolecularly,which will give rise to a number of conformationally different molecules in the solidstate. 234-236 Thus the extra bands observed in the solid state are due to the differencesin sample dynamics between the two methods. In solution, anisotropic NMRinteractions are averaged to zero to give the observed chemical shifts as sharpisotropic signals. 237, 238 In the solid, state, however, the molecules are virtually staticand because of this anisotropic or orientation-dependent interactions can beobserved. 237, 238 Furthermore, polymorphism within the powder structure puts someof the carbon atoms into different environments and, as solid state NMR candistinguish these different molecular conformations in addition to configurationaldissimilarities in a segment of a molecule the spectra obtained display a more239, 240complex pattern for some resonances.In examining spectrum D for evidence of the inclusion of 2,6-dihydroxybenzoate114