Studies of lead(II) complexes of substituted calix[4]diquinones: the remarkable self-assembly of a novel redox-active 3D channel network

Several calix[4]diquinone-lead(II) complexes have been prepared. Two monomeric complexes have been prepared with p-tert-butyl-(26,28-crown-5)calix[4]diquinone L-1 and p-tert-butylcalix[4]diquinone bis(ethyl ether) L-2, namely [PbL1(ClO4)(2)] and [PbL2(ClO4)(2)(H2O)] wherein the metal atoms are 10-coordinate being bonded to the four oxygen atoms at the lower rim of the calixdiquinone and three perchlorate oxygen atoms together with three crown oxygen atoms or two carbonyl oxygen atoms and a water molecule respectively. By contrast the lead(II) complex with calix[4]diquinone bis(acid) L-3 forms a unique trimeric [Pb-9(L-3-2H)(3)(ClO4)(6)(OH)(6)] unit with crystallographic 3/m symmetry containing three unique Pb(II) atoms. One of these is to be found within the calix[4]diquinone bonded to the four oxygen atoms at the lower rim, two acid oxygen atoms, two perchlorate anions and a water molecule. The other two Pb(II) atoms are bonded to carbonylic oxygen atoms, water molecules and hydroxide ions. These trimeric units are interconnected via upper rim quinone oxygen-Pb(II) interactions to form a three-dimensional network containing channels of ca. 14 angstrom in diameter.