A new tubular arrangement of a dimethylsilyl bridged calix[4] resorcinarene

The functionalization of calix[4]resorcinarene 1 (R-1 = H, R-2 = Me) with d ichlorodimethylsilane leads to the formation of the dimethylsilyl-bridged c avitand 2 which, during the work up of the reaction product, encapsulates a molecule of water. 2 H2O crystallizes in the C2/c system (a = 23.892 Angst rom, b = 8.493 Angstrom, c = 43.035 Angstrom, beta = 100.05 degrees reflect ions: 5385, 2376 (F > 4.0 sigma(F)), R = 9.17%, calculated density = 1.213 Mg/m(3)) with eight molecules per unit cell. The main feature of the crysta l packing is the alternating pairs of up-down disposed cavitands along the c direction and well developed columns in the b direction. The molecules of water are completely encapsulated, but there are some close contacts with the methylene bridge from the upper molecule. Molecular orbital calculation s show that the lowest energy conformer of cavitand 2 is that with all four silicon atoms oriented inward and the energies of the other conformers are so high that they cannot be accessed at normal temperature. Ab initio calc ulated electrostatic potentials correlate well with the relative positions of the cavitands in the crystal structure.