Ag^I and Pb^II as Additional Assembling Cations in Uranyl Coordination Polymers and Frameworks

Abstract

Five mono-or polycarboxylic acids have been used to generate a series of eight heterometallic uranyl complexes involving silver(I) or lead(II) cations, all synthesized under (solvo)-hydrothermal conditions. Pimelic acid (H2pim) gave complexes [Ag(bipy)2]2[UO2(pim)(NO3)]2 (1) and [UO2Pb(pim)2(bipy)(H2O)]0.5bipyH2O (2) (bipy = 2,2ʹ-bipyridine), which both crystallize as one-dimensional (1D) polymers, but differ in that the silver(I) cations are separate counter-ions, while carboxylate-bound lead(II) cations are an essential component of the polymer. Only silver(I)-containing species were obtained with all-cis 1,3,5-cyclohexanetricarboxylic acid (H3chtc), [UO2Ag(chtc)(H2O)2] (3) and [Ag(bipy)(CH3CN)]2[UO2(chtc)]2 (4); both contain two-dimensional (2D) uranyl carboxylate subunits with honeycomb {6 3 } topology, these being united into a three-dimensional (3D) framework with the lonsdaleite {6 6 } topology by bridging, oxo-bound silver(I) cations in 3. Both silver-and lead-containing complexes were obtained with 3,3ʹ,4,4ʹ-biphenyltetracarboxylic acid (H4bptc), [UO2Ag(bptc)(4,4ʹ-bipyH)] (5) and [UO2Pb(bptc)(bipy)2] (6) (4,4ʹ-bipy = 4,4ʹ-bipyridine), and they both display a 2D uranyl carboxylate network with the {4 4 .6 2 } topology, the additional cations and N-donors being decorating species. In this case, a higher dimensionality was obtained not with an additional cation, but with a coordinated N-methyl-2-pyrrolidone (NMP) molecule, since [(UO2)2(bptc)(NMP)1.5(H2O)1.5]1.5H2O (7) crystallizes as a three-dimensional (3D) framework. In the presence of silver(I), 3-pyrimidin-2-yl-benzoic acid (Hpyb) gave the complex [UO2Ag(pyb)3(H2O)2]4H2O (8), in which the two coordination sites are occupied in accord with Hard/Soft Acid/Base (HSAB) principles, uranyl being chelated by three carboxylate groups and silver(I) being bound to nitrogen atoms; the 1D polymer formed bridges to another through silver-uranyl oxo bonding. In contrast, the homometallic, molecular complex [UO2(pyb)2(bipy)] (9) was obtained in the presence of lead(II) cations. The lead-containing complex with 2,6-pyridinedicarboxylic acid (H2pydc), [UO2Pb2(pydc)2(phen)2(HCOO)1.5(NO3)0.5]0.5H2O (10) (phen = 1,10-phenanthroline), crystallizes as a 1D polymer in which uranyl is bound to two O,N,O-donors, as usual with this ligand, polymerization being due to lateral double lead(II) bridges. Variations in uranyl emission maxima positions appear to be essentially related to the uranium coordination number within the present series.

Structural Consequences of 1,4-Cyclohexanedicarboxylate Cis/Trans Isomerism in Uranyl Ion Complexes: From Molecular Species to 2D and 3D Entangled Nets

“…These latter contacts may represent very weak interactions at best (in particular, uranyl oxo bonding to Pb II with a much shorter distance of 2.999(4) Å has been reported 67 ) and, if they are disregarded, both Pb II cations are in seven-coordinate environments with a geometry of the tetragonal base-trigonal base type, 68 to energy transfer to a d-d excited state followed by non-radiative decay, 12,29,32,35,63,64,70 while energy transfer to an isolated Cu I centre, possibly involving a d-s excited state, would be expected to give rise at most to a weak Cu I emission. 71 Quenching due to the presence of lead(II) has been previously observed, 67,72 although it is not general, 4,49 and its origins are obscure. In all the other cases, the vibronic progression corresponding to the S11 → S00 and S10 → S0ν (ν = 0-4) electronic transitions 73 is apparent, with four or five intense and well-resolved peaks, as shown in Figure 15, the positions of these emission bands being dependent on the nature and number of donor atoms in the uranyl equatorial plane.…”

“…4,5,12,35,37,73,81,82 So as to get a visual representation of the dependence of the peaks positions upon the geometry of the uranyl equatorial environment, the positions of the four main peaks [S10 → S0ν (ν = 0-3)] have been plotted in Figure 16 for a series of 46 complexes involving various polycarboxylate ligands (including also the present results). 4,5,12,32,35,37,49,51,64,67,72,[77][78][79][80][83][84][85] All these complexes are from our own work, so that all measures have been performed using the same apparatus and in exactly the same conditions, and only well resolved spectra of complexes having only one kind of equatorial environment have been considered; the precision of the measurements can be estimated at ±2 nm. The complexes are separated into four groups according to the number and nature of equatorial donors, O6, O4N2, O5 or O4, and the complexes are sorted within each group in the order of red-shift of the lowest wavelength emission peak, so that shifts in the positions of the three other peaks between different complexes reveal slight variations of the splitting energy.…”

1,2-, 1,3-, and 1,4-Phenylenediacetate Complexes of the Uranyl Ion with Additional Metal Cations and/or Ancillary N-Donor Ligands: Confronting Ligand Geometrical Proclivities

“…[33][34][35] In complex 8, the chains are arranged Two complexes in this series, with the 1,3-and 1,4-PDA 2ligands, contain the Pb(phen) 2+ moiety as part of the neutral polymeric assembly, as is generally the case with this group or with Pb(bipy) 2+ due to the affinity of Pb 2+ for carboxylate donors which prevents its separation as a purely N-chelated complex. [36][37][38][39] In complex [UO2Pb(1,3-PDA)2(phen)] (10), the unique uranyl cation is chelated by three carboxylate groups, while lead(II) is chelated by one carboxylate and phen, and is also bound to two more carboxylate oxygen atoms and the uranyl oxo atom O1 (Figure 8).  been found in "Pacman" macrocyclic complexes.…”

Structure-Directing Effects of Counterions in Uranyl Ion Complexes with Long-Chain Aliphatic α,ω-Dicarboxylates: 1D to Polycatenated 3D Species

“…[7][8][9] These bipyridyl species assume the various roles of coligands, counterions, and structure-directing species, depending on their length compared to that of the dicarboxylates. Other diverse species, either neutral such as cucurbiturils, 10 2,2ʹ-bipyridine (bipy) or 1,10-phenanthroline (phen), 11 or cationic such as NH4 + , 12 H2NMe2 + , 13 [M(L)x] n+ , with M = Mn, Fe, Co, Ni, Cu, Ag, L = bipy or phen, x = 2 or 3 and n = 1 or 2, 12,[14][15][16][17] [Co(en)3] 3+ , with en = ethylenediamine, 12 or Pb 2+ , 17 have also been found to act as structure-directing agents in uranyl ion complexes with Cn 2-(n = 6-10, 12, 13 and 15), whether they be neutral co-crystallized species, coligands, counterions or additional metal groups included in the polymer. species displaying Borromean-type entanglement.…”