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)
Résumé
Reaction of uranyl nitrate with 1,3,5-benzenetriacetic acid (H 3 BTA) 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(NH 2) 3 ][UO 2 (BTA)]·H 2 O (1) and [H 2 NMe 2 ]-[UO 2 (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 con-formations. One of the bound carboxylate units is replaced by chelating 1,10-phenanthroline (phen) or 3,4,7,8-tetramethyl-1,10-phenanthroline (Me 4 phen) in the complexes [(UO 2) 3 (BTA) 2 (phen) 3 ]·4H 2 O (3) and [(UO 2) 3 (BTA) 2 (Me 4 phen) 3 ]·NMP·3H 2 O (4) (NMP = N-methyl-2-pyrrolidone), which are a 2D network with honeycomb topology and a 1D polymer, respectively. With silver(I) cations, [UO 2 Ag(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 [UO 2 Pb(BTA)(NO 3)(bipy)] (6) and [UO 2 Pb 2 (BTA) 2 (bipy) 2 ]·3H 2 O (7), where bipy is 2,2′-bipyridine, crystallize from the one solution, as 1D and 2D assemblies, respectively. The two 1D coordination polymers [UO 2 Pb(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 [(UO 2) 2 Pb 2 (BTA) 2 (HBTA)(H 2 O) 2 (phen) 2 ]·2H 2 O (10), which provides a possible example of a Pb−oxo(uranyl) " cation−cation " interaction. While [UO 2 Pb(BTA)(HCOO) 0.5 (NO 3) 0.5 (Me 2 phen)] (11), where Me 2 phen is 5,6-dimethyl-1,10-phenanthroline, is a 1D assembly close to those in 6 and 8, [UO 2 Pb 2 (BTA) 2 (Me 4 phen) 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. ■ INTRODUCTION The formation of solid frameworks incorporating cavities suited to selective absorption of molecular species and involving uranyl ion centers within the framework 1 has, as obvious potential applications, sensing due to changes in luminescence and catalytic photo-oxidation of any absorbed species. 2 Although an isolated uranyl center is a one-electron photo-oxidant, 2c,d the possibility of arranging multiple uranyl centers about a single cavity in a solid raises the prospect of performing a variety of multielectron oxidations. Despite the extensive characterization of uranyl−organic coordination polymers and frameworks, however, systems that might be suitable for such applications have been obtained more by chance than design, and in the majority of cases only those that can be considered polyuranate derivatives have uranium(VI) centers in close proximity. The remarkable family of peroxo-bridged poly-uranates provides elegant examples of this situation. 3 It is known that uranyl luminescence is subject to numerous influences, 4 including the presence of other uranyl centers and of a variety of transition metal ions, 5,6 so that the systematic investigation of mixed-metal uranyl coordination polymers would seem a rational pathway to applications of uranyl ion photochemistry. Recent reports by us and other groups have dealt with the investigation of the crystal structure and luminescence properties of uranyl ion complexes, coordination polymers or frameworks including 3d block metal cations either as additional metal centers in the complex unit or as counterions, the ligands used being polycarboxylates or polyphosphonates. 5,6 The present work is an extension of this survey to a poly(carboxylic acid), which has been little used in uranyl chemistry, 1,3,5-benzenetriacetic acid (H 3 BTA), the