O. Mogck et al., HYDROGEN-BONDED DIMERS OF TETRAUREA CALIX[4]ARENES - UNAMBIGUOUS PROOF BY SINGLE-CRYSTAL X-RAY-ANALYSIS, Chemical communications, (22), 1996, pp. 2533-2534
Self-assembly of calix[4]arenes substituted by four urea residues at t
he wider rim leads to hydrogen-bonded dimers; the first single crystal
X-ray analysis of such a dimer is reported.