Synthesis and crystal structures of 5,17-dibromo-26,28-dihydroxy-25,27-dipropynyloxycalix[4]arene, 5,17-dibromo-26,28-dipropoxy-25,27-dipropynyloxycalix[4]arene and 25,27-bis(2-azidoethoxy)-5,17-dibromo-26,28-dihydroxycalix[4]arene

Abstract

The calixarenes, 5,17-dibromo-26,28-dihydroxy-25,27-dipropynyloxycalix[4]arene (C34H26Br2O4, 1), 5,17-dibromo-26,28-dipropoxy-25,27-dipropynyloxycalix[4]arene (C40H38Br2O4, 2) and 25,27-bis(2-azidoethoxy)-5,17-dibromo-26,28-dihydroxycalix[4]arene (C32H28Br2N6O4, 3) possess a pinched cone molecular shape for 1 and 3, and a 1,3-alternate shape for compound 2. In calixarenes 1 and 3, the cone conformations are additionally stabilized by intramolecular O—H...O hydrogen bonds, while in calixarene 2 intramolecular Br...Br interactions consolidate the 1,3-alternate molecular conformation. The dense crystal packing of the cone dialkyne 1 is a consequence of π–π, C—H...π and C—H...O interactions. In the crystal of the diazide 3, there are large channels extending parallel to the c axis, which are filled by highly disordered CH2Cl2 solvent molecules. Their contribution to the intensity data was removed by the SQUEEZE procedure that showed an accessible void volume of 585 Å3 where there is room for 4.5 CH2Cl2 solvent molecules per unit cell. Rigid molecules of the 1,3-alternate calixarene 2 form a columnar head-to-tail packing parallel to [010] via van der Waals interactions, and the resulting columns are held together by weak C—H...π contacts.