Uranyl Tricarballylate Triperiodic and Nanotubular Species. Counterion Control of Nanotube Diameter
Résumé
Tricarballylic acid (propane-1,2,3-tricarboxylic acid, H3 tca) was reacted with uranyl nitrate hexahydrate under solvo-hydrothermal conditions and in the presence of different additional cations, yielding four complexes which have been crystallographically characterized. [(UO2)2Ba(tca)2(H2O)4] (1), isomorphous to the PbII analogue previously reported, crystallizes as a triperiodic framework in which diperiodic uranyl–tca3– subunits with the hcb (honeycomb) topology are linked by carboxylate-bound BaII cations. Triperiodic polymerization is also found in [(UO2)2(tca)2Ni(cyclam)] (2) and [(UO2)2(tca)2Cu(R,S-Me6cyclam)] (3), but here the diperiodic uranyl–tca3– subunits have the sql (square lattice) topology, and the frameworks formed through bridging by NiII or CuII cations have different topologies, tcs in 2 and xww in 3. [Co(en)3][UO2(tca)]3·2H2O (4) crystallizes as a monoperiodic coordination polymer with the hcb topology and a nanotubular geometry. In contrast to the square-section nanotubules previously found in [NH4][(UO2)2Pb(tca)2(NO3)(bipy)] (bipy = 2,2′-bipyridine), those in 4 have a hexagonal section with a width of ∼7 Å. The structure-directing role of the hydrogen bonded counterions in these nanotubular species, either NH4+ located within the nanotubule cavity or [Co(en)3]3+ located outside, is discussed. Emission spectra in the solid state display the usual vibronic fine structure for 1 and 4, while uranyl emission is quenched in 3.