Modulation of the Structure and Properties of Uranyl Ion Coordination Polymers Derived from 1,3,5-Benzenetriacetate by Incorporation of Ag(I) or Pb(II)

Reaction of uranyl
nitrate with 1,3,5-benzenetriacetic acid (H3BTA) in the
presence of additional species, either organic bases or their conjugate
acids or metal cations, has provided 12 new crystalline complexes,
all but one obtained under solvo-hydrothermal conditions. The complexes
[C­(NH2)3]­[UO2(BTA)]·H2O (1) and [H2NMe2]­[UO2(BTA)] (2) crystallize as one- or two-dimensional
(1D or 2D) assemblies, respectively, both with uranyl tris-chelation
by carboxylate groups and hydrogen-bonded counterions but different
ligand conformations. One of the bound carboxylate units is replaced
by chelating 1,10-phenanthroline (phen) or 3,4,7,8-tetramethyl-1,10-phenanthroline
(Me4phen) in the complexes [(UO2)3(BTA)2­(phen)3]·4H2O (3) and [(UO2)3­(BTA)2­(Me4phen)3]·NMP·3H2O (4) (NMP = N-methyl-2-pyrrolidone),
which are a 2D network with honeycomb topology and a 1D polymer, respectively.
With silver­(I) cations, [UO2Ag­(BTA)] (5),
a three-dimensional (3D) framework in which the ligand assumes various
chelating/bridging coordination modes, and the aromatic ring is involved
in Ag­(I) bonding, is obtained. A series of seven heterometallic complexes
results when lead­(II) cations and N-chelating molecules are both present.
The complexes [UO2Pb­(BTA)­(NO3)­(bipy)]
(6) and [UO2Pb2­(BTA)2­(bipy)2]·3H2O (7), where bipy is 2,2′-bipyridine, crystallize from the one
solution, as 1D and 2D assemblies, respectively. The two 1D coordination
polymers [UO2Pb­(BTA)­(HCOO)­(phen)] (8 and 9), again obtained from the one synthesis, provide
an example of coordination isomerism, with the formate anion bound
either to lead­(II) or to uranyl cations. Another 2D architecture is
found in [(UO2)2Pb2(BTA)2­(HBTA)­(H2O)2(phen)2]·2H2O (10), which provides a possible example of
a Pb–oxo­(uranyl) “cation–cation” interaction.
While [UO2Pb­(BTA)­(HCOO)0.5(NO3)0.5­(Me2phen)] (11), where
Me2phen is 5,6-dimethyl-1,10-phenanthroline, is a 1D assembly
close to those in 6 and 8, [UO2Pb2(BTA)2­(Me4phen)2] (12), obtained together with complex 4, crystallizes as a 2D network as a result of the high degree of
connectivity provided by the chelating/bridging tricarboxylate ligand.
Emission spectra measured in the solid state display vibronic fine
structure attributable to uranyl luminescence (except for complex 5, in which emission is quenched), with variations in maxima
positions associated with modifications of the uranyl ion environment.