Complexation behaviour of p-tert-butylcalix[4]arene and p-tert-butylcalix[6]arene towards acetone

Novel 1:1 complexes of acetone with p-tert-butylcalix[4]arene and p-tert-butylcalix[6]arene were prepared and characterized by TGA, DSC, PXRD and C-13 and H-2 solid-state NMR. The behaviour of both molecules towards acetone is very similar, with the same orientation of the guest, and the same activation energy for the rotation of the C-D bond of acetone about its threefold axis. This is interpreted in terms of the pinched-cone conformation of p-tert-bultylcalix[6]arene in the complex, which can be viewed as two edge-sharing p-tert-bultylcalix[4]arene molecules in the cone conformation.