Abstract
p-Bu-t-calix[5]arene forms crystalline inclusion complexes with o- and m-carboranes in toluene or dichloromethane-hexane, but not with the p-isomer, the extended structures being based on 1:1 host-guest supermolecules, with the p-Bu-t-substituents creating a snug fit for o- and m-carborane; p-carborane forms a highly hexane soluble complex, induced by grinding, which crystallizes as fibres. Solution phase studies showed the presence of a 1:1 host-guest stoichiometry with all three isomeric carboranes as determined from Job plots. The association constants for the o- and m-carborane complexes are 6.4 +/- 0.3 M-1 and 3.8 +/- 0.1 M-1 respectively, whereas the p-isomer is only weakly associated. Competition experiments involving all three isomers show rapid exchange on the NMR time scale, and no selectivity in solution is evident. Selective association involving the o- and m-isomers in the solid state is therefore remarkable, and it is a manifestation of crystal packing forces which embodies the differences in dipole moments of the carboranes.
Original language | English |
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Pages (from-to) | 5449-5453 |
Journal | Dalton Transactions |
Volume | 2006 |
Issue number | 46 |
DOIs | |
Publication status | Published - 2006 |