Cavity Formation in Uranyl Ion Complexes with Kemp's Tricarboxylate: Grooved Diperiodic Nets and Polynuclear Cages.

Kemp's triacid (-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid, Hkta) was reacted with uranyl nitrate under solvo-hydrothermal conditions in the presence of diverse counterions or additional metal cations to give eight zero- or diperiodic complexes. All the coordination polymers in the series, [PPhMe][UO(kta)]·0.5HO (), [PPh][UO(kta)] (), [C(NH)][UO(kta)] (), [Cd(bipy)][UO(kta)] (), and [Zn(phen)][UO(kta)]·2HO () (bipy = 2,2'-bipyridine, phen = 1,10-phenanthroline) crystallize as networks with the topology, the ligand being in the chair conformation with the three carboxylate groups equatorial, except in , in which the axial/diequatorial boat conformation is present. Various degrees of corrugation and different arrangements of neighboring layers are observed depending on the counterion, with complexes and , in particular, displaying cavities containing the bulky cations. [Co(en)][(UO)(kta)(Hkta)]·2NMP·10HO () (en = 1,2-ethanediamine; NMP = -methyl-2-pyrrolidone) contains a metallatricyclic, tetranuclear anionic species, displaying two clefts in which the cations are held by extensive hydrogen bonding, and with the ligands in both triaxial chair and axial/diequatorial boat conformations. [(UO)Pb(kta)(Hkta)(HO)]·1.5THF () (THF = tetrahydrofuran) and [(UO)Pb(kta)(Hkta)(NMP)] () are two heterometallic cage compounds containing only the convergent, triaxial chair form of the ligand, which have the same topology in spite of the different U/Pb ratio. These complexes are compared to previous ones also involving Kemp's triacid anions, and the roles of ligand conformation and of counterions in the formation of cavities, either in cage-like species or as grooves in diperiodic networks, is discussed.