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

Kemp's triacid (cis,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid, H(3)kta) 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, [PPh3Me][UO2(kta)]center dot 0.5H(2)O (1), [PPh4][UO2(kta)] (2), [C(NH2)(3)][UO2(kta)] (3), [Cd(bipy)(3)][UO2(kta)](2) (4), and [Zn(phen)(3)][UO2(kta)](2)center dot 2H(2)O (5) (bipy = 2,2'-bipyridine, phen = 1,10-phenanthroline) crystallize as networks with the hcb topology, the ligand being in the chair conformation with the three carboxylate groups equatorial, except in 3, 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 4 and 5, in particular, displaying cavities containing the bulky cations. [Co(en)(3)](2)[(UO2)(2)-(kta)(Hkta)(2)](2)center dot 2NMP center dot 10H(2)O (6) (en = 1,2-ethanediamine; NMP = N-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. [(UO2)(3)Pb(kta)(2)(Hkta)(H2O)] 2 center dot 1.5THF (7) (THF = tetrahydrofuran) and [(UO2)(2)Pb-2(kta)(2)(Hkta)(NMP)](2) (8) 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.

Automated summary

Kemp's triacid can react with uranyl nitrate to form various complexes with different crystal forms and counterions, some of which exhibit cavities containing bulky cations. These complexes show diverse arrangements of neighboring layers and different degrees of corrugation depending on the counterion.