Tubelike Uranyl-Phenylenediacetate Assemblies from Screening of Ligand Isomers and Structure-Directing Counterions

Woven, Polycatenated, or Cage Structures: Effect of Modulation of Ligand Curvature in Heteroleptic Uranyl Ion Complexes

Combining the flexible zwitterionic dicarboxylate 4,4'-bis(2-carboxylatoethyl)-4,4'-bipyridinium (L) and the anionic dicarboxylate ligands isophthalate (ipht^2-) and 1,2-, 1,3-, or 1,4-phenylenediacetate (1,2-, 1,3-, and 1,4-pda^2-), of varying shape and curvature, has allowed isolation of five uranyl ion complexes by synthesis under solvo-hydrothermal conditions. [(UO₂)₂(L)(ipht)₂] (1) and [(UO₂)₂(L)(1,2-pda)₂]·2H₂O (2) have the same stoichiometry, and both crystallize as monoperiodic coordination polymers containing two uranyl-(anionic carboxylate) strands united by L linkers into a wide ribbon, all ligands being in the divergent conformation. Complex 3, [(UO₂)₂(L)(1,3-pda)₂]·0.5CH₃CN, with the same stoichiometry but ligands in a convergent conformation, is a discrete, binuclear species which is the first example of a heteroleptic uranyl carboxylate coordination cage. With all ligands in a divergent conformation, [(UO₂)₂(L)(1,4-pda)(1,4-pdaH)₂] (4) crystallizes as a sinuous and thread-like monoperiodic polymer; two families of chains run along different directions and are woven into diperiodic layers. Modification of the synthetic conditions leads to [(UO₂)₄(LH)₂(1,4-pda)₅]·H₂O·2CH₃CN (5), a monoperiodic polymer based on tetranuclear (UO₂)₄(1,4-pda)₄ rings; intrachain hydrogen bonding of the terminal LH⁺ ligands results in diperiodic network formation through parallel polycatenation involving the tetranuclear rings and the LH⁺ rods. Complexes 1-3 and 5 are emissive, with complex 2 having the highest photoluminescence quantum yield (19%), and their spectra show the maxima positions usual for tris-κ²O,O'-chelated uranyl cations.

Zwitterionic and Anionic Polycarboxylates as Coligands in Uranyl Ion Complexes, and Their Influence on Periodicity and Topology

The three zwitterionic di- and tricarboxylate ligands 1,1'-[(2,3,5,6-tetramethylbenzene-1,4-diyl)bis(methylene)]bis(pyridin-1-ium-4-carboxylate) (pL1), 1,1'-[(2,3,5,6-tetramethylbenzene-1,4-diyl)bis(methylene)]bis(pyridin-1-ium-3-carboxylate) (mL1), and 1,1',1″-[(2,4,6-trimethylbenzene-1,3,5-triyl)tris(methylene)]tris(pyridin-1-ium-4-carboxylate) (L2) have been used as ligands to synthesize a series of 15 uranyl ion complexes involving various anionic coligands, in most cases polycarboxylates. [(UO₂)₂(pL1)₂(cbtc)(H₂O)₂]·10H₂O (1, cbtc^4- = cis,trans,cis-1,2,3,4-cyclobutanetetracarboxylate) is a discrete, dinuclear ring-shaped complex with a central cbtc^4- pillar. While [UO₂(pL1)(NO₃)₂] (2), [UO₂(pL1)(OAc)₂] (3), and [UO₂(pL1)(HCOO)₂] (4) are simple chains, [(UO₂)₂(mL1)(1,3-pda)₂] (5, 1,3-pda^2- = 1,3-phenylenediacetate) is a daisy chain and [UO₂(pL1)(pdda)]₃·10H₂O (6, pdda^2- = 1,2-phenylenedioxydiacetate) is a double-stranded, ribbon-like chain. Both [UO₂(pL1)(pht)]·5H₂O (7, pht^2- = phthalate) and [(UO₂)₃(mL1)(pht)₂(OH)₂] (8) crystallize as diperiodic networks with the sql topology, the latter involving hydroxo-bridged trinuclear nodes. [(UO₂)₂(pL1)(c/t-1,3-chdc)₂] (9, c/t-1,3-chdc^2- = cis/trans-1,3-cyclohexanedicarboxylate) and [UO₂(pL1)(t-1,4-chdc)]·1.5H₂O (10, t-1,4-chdc^2- = trans-1,4-cyclohexanedicarboxylate) are also diperiodic, with the V₂O₅ and sql topologies, respectively. Both [(UO₂)₂(mL1)(c/t-1,4-chdc)₂] (11) and [(UO₂)₂(pL1)(1,2-pda)₂] (12, 1,2-pda^2- = 1,2-phenylenediacetate) crystallize as diperiodic networks with hcb topology, and they display threefold parallel interpenetration. [HL2][(UO₂)₃(L2)(adc)₃]Br (13, adc^2- = 1,3-adamantanedicarboxylate) contains a very corrugated hcb network with two different kinds of cells, and the uncoordinated HL2⁺ molecule associates with the coordinated L2 to form a capsule containing the bromide anion. [(UO₂)₂(pL1)(kpim)₂] (14, kpim^2- = 4-ketopimelate) is a three-periodic framework with pL1 molecules pillaring fes diperiodic subunits, whereas [(UO₂)₂(L2)₂(t-1,4-chdc)](NO₃)_1.7Br_0.3·6H₂O (15), the only cationic complex in the series, is a triperiodic framework with dmc topology and t-1,4-chdc^2- anions pillaring fes diperiodic subunits. Solid-state emission spectra and photoluminescence quantum yields are reported for all complexes.

Ni(2,2':6',2″-Terpyridine-4'-carboxylate)2 Zwitterions and Carboxylate Polyanions in Mixed-Ligand Uranyl Ion Complexes with a Wide Range of Topologies

The zwitterionic complex formed by Ni^II and 2,2':6',2″-terpyridine-4'-carboxylate, Ni(tpyc)₂, has been used as a coligand with a diverse group of polycarboxylates in uranyl ion complexes synthesized under solvo-hydrothermal conditions, thus giving a series of 14 mixed ligand, heterometallic compounds. Both [(UO₂)₂(c-1,2-chdc)Ni(tpyc)₂(NO₃)₂]₂·4CH₃CN (1) and [(UO₂)₂(tdc)Ni(tpyc)₂(NO₃)₂]₂ (2), where c-1,2-chdc^2- is cis-1,2-cyclohexanedicarboxylate and tdc^2- is 2,5-thiophenedicarboxylate, display discrete U₄Ni₂ dinickelatetrauranacycles, a motif which is also found as part of a daisychain coordination polymer in [(UO₂)₄(bdc)₃Ni₂(tpyc)₄(NO₃)₂]·2CH₃CN·2H₂O (3), where bdc^2- is 1,4-benzenedicarboxylate. Similar U₄Ni₂ rings associate to form a nanotubular polymer in [(UO₂)₂(tca)Ni(tpyc)₂(NO₃)]·2CH₃CN·2H₂O (4), where tca^3- is tricarballylate. [(UO₂)₂(1,2-pda) (1,2-pdaH)Ni(tpyc)₂(NO₃)]·CH₃CN (5), where 1,2-pda^2- is 1,2-phenylenediacetate, crystallizes as a meander-like chain in which each bent section can be seen as an open, semi-U₄Ni₂ ring. Oxalate (ox^2-) gives [(UO₂)₂(ox)₂Ni(tpyc)₂] (6), a monoperiodic polymer containing smaller U₄Ni rings, while 1,2,3-benzenetricarboxylate (1,2,3-btc^3-) and citrate (citH^3-) give [Ni(tpycH)(H₂O)₃][UO₂(1,2,3-btc)]₂·2H₂O (7) and [UO₂Ni₂(tpyc)₄][UO₂(citH)]₂ (8), two complexes with charge separation, the latter displaying one-periodic + two-periodic semi-interpenetration. [(UO₂)₂(btcH)Ni(tpyc)₂(NO₃)] (9) and [(UO₂)₂(cbtcH)Ni(tpyc)₂(NO₃)] (10), where btc^4- and cbtc^4- are 1,2,3,4-butanetetracarboxylate and cis,trans,cis-1,2,3,4-cyclobutanetetracarboxylate, respectively, are diperiodic networks with hcb topology, and [(UO₂)₂(ndc)Ni(tpyc)₂(OH)(NO₃)] (11), where ndc^2- is 2,6-naphthalenedicarboxylate, is a sql network containing dinuclear nodes and involving 100-membered U₁₀Ni₄ metallacyclic units. U₄Ni₂ rings are found in the diperiodic polymer formed in [(UO₂)₄(t-R-1,2-chdc)₄Ni₂(tpyc)₄] (12), where t-R-1,2-chdc^2- is trans-R,R-1,2-cyclohexanedicarboxylate, the heavily puckered sheets being interlocked. 1,3-Phenylenediacetate (1,3-pda^2-) gives a very thick diperiodic polymer with KIa topology, [(UO₂)₄(1,3-pda)₄Ni₂(tpyc)₄]·CH₃CN·2H₂O (13). A triperiodic framework is formed with nitrilotriacetate (nta^3-) in [(UO₂)₂(nta)₂Ni₂(tpyc)₂] (14), where Ni^II is found in Ni(tpyc)₂ units as well as in Ni(nta)₂^4- moieties which both act as 4-coordinated nodes.

Structural diversity induced by ligand geometry: From two-dimensional to three-dimensional coordination polymers with pyridine

Two coordination polymers with two-dimensional and three-dimensional structures are, {[Zn3(bdc)3(py)2]·2NMP}n (1) (H2bdc = 1,4-benzenedicarboxylic acid) and [Zn2(NO3−)(btc)(nmp)2(py)]n (2) (H3btc = 1,3,5-benzenetricarboxylic acid), synthesized by hot-solution reactions of Zn(NO3)2·6H2O, pyridine (py) and two different ligands in N-methylpyrrolidone (NMP). {[Zn3(bdc)3(py)2]·2NMP}n exhibits two-dimensional networks with trizinc subunits [Zn3(COO)6py2] stacking with a layer-by-layer alignment, and there are strong π–π interactions involving py from adjacent layers. [Zn2(NO3−)(btc)(nmp)2(py)]n has a three-dimensional structure containing two independent zinc ions, tetrahedral ZnO4 and octahedral ZnNO5. Based on X-ray studies, the coordination polymers {[Zn3(bdc)3(py)2]·2NMP}n (1) have a porous structure with NMP guest molecules. In contrast, X-ray studies revealed that coordination polymer [Zn2(NO3−)(btc)(nmp)2(py)]n (2) had a larger void that was inhabited by coordinated py and NMP. In addition, the form of the two coordination polymers changed from two-dimensional to three-dimensional with transformation of the ligand geometry.

Variability of Uranyl Carboxylates from Rigid Terophenyldicarboxylic Acid Ligands

Three uranyl carboxylates, namely, (UO₂)(L¹)(H₂O)_0.5 (1), [(UO₂)(L²)(H₂O)]·2H₂O (2), and [(UO₂)(L²)(H₂O)]·(CH₃CN) (3), were synthesized hydrothermally from 2',3',5',6'-tetramethyl-(1,1':4',1″-terphenyl)-4,4″-dicarboxylic acid (H₂L¹) and 2',5'-dimethyl-(1,1':4',1″-terphenyl)-3,3″-dicarboxylic acid (H₂L²), which are all steric carboxylic acid ligands but vary with the carboxylic acid group position and methyl group number. It is found that compound 1 displays a three-dimensional 8-fold-interpenetrated net with channels running along the c direction. Compounds 2 and 3 are isostructural, and all display two-dimensional-layered crystal structures but contain different guest molecules. The photophysical measurements reveal that compounds 1 and 2, which contain disordered water molecules, are luminescence-quenched, whereas compound 3 containing acetonitrile molecules is luminescent.

Uranyl Tricarballylate Triperiodic and Nanotubular Species. Counterion Control of Nanotube Diameter

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 Pb^II analogue previously reported, crystallizes as a triperiodic framework in which diperiodic uranyl-tca^3- subunits with the hcb (honeycomb) topology are linked by carboxylate-bound Ba^II 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-tca^3- subunits have the sql (square lattice) topology, and the frameworks formed through bridging by Ni^II or Cu^II 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.

Uranyl Organic Framework as a Highly Selective and Sensitive Turn-on and Turn-off Luminescent Sensor for Dual Functional Detection Arginine and MnO4. Inorg Chem 2020;59:5004-5017. [PMID: 32207299 DOI: 10.1021/acs.inorgchem.0c00236]

Five new uranyl coordination polymers were prepared by the hydrothermal method based on 5-nitroisophthalic acid (H₂nip) as (UO₂)(nip)(2,2'-bpy) (1), (H₂4,4'-bpy)·[(UO₂)₃(nip)₄]·(4,4'-bpy) (2), (H₂bpe)·[(UO₂)_0.5(nip)] (3), (H₂ bpp)·[(UO₂)₂-(nip)₃]·H₂O (4), and (H₂tmp)·[(UO₂)(nip)₂](5) [2,2'-bpy = 2,2'-bipyridine, 4,4'-bpy = 4,4'-bipyridine, bpe = 4,4'-vinylenedipyridine, bpp = 4,4' -trimethylenedipyridine, tmp = tetramethylpyrazine]. All of these synthesized complexes have been characterized by single crystal and powder X-ray diffraction, IR spectra, thermogravimetric analysis, elemental analysis, and luminescent properties. In particular, it is found that compounds 1 and 4 can be used as a luminescent sensor to efficiently detect arginine in aqueous solution by means of "turn-on"; the detection limits were 1.06 × 10^-6 and 6.42 × 10^-6 mol/L, respectively. Moreover, 4 can also be used as a bifunctional sensor for selective sensing of MnO₄^- anion by "turn-off". The detection limit of MnO₄^- in water was 1.79 × 10^-6 mol/L; the K_sv was 1.88 × 10⁴. The sensing effect of arginine in simulated grape juice samples and MnO₄^- in simulated river water samples was also investigated by this sensing system with high recovery. In addition, the possible mechanism of sensing arginine and MnO₄^- in the aqueous solution was discussed.

Functionalized Aromatic Dicarboxylate Ligands in Uranyl-Organic Assemblies: The Cases of Carboxycinnamate and 1,2-/1,3-Phenylenedioxydiacetate

2-Carboxycinnamic acid (ccnH₂) and the isomeric 1,2- and 1,3-phenylenedioxydiacetic acids (1,2- and 1,3-pddaH₂) have been used to synthesize eight uranyl ion complexes under solvo-hydrothermal conditions. In the four complexes [PPh₄]₂[UO₂(ccn)(NO₃)]₂ (1), [PPh₄]₂[UO₂(ccn)(dibf)]₂ (2), [UO₂(ccn)(bipy)]₂ (3), and [Ni(R,S-Me₆cyclam)][UO₂(ccn)(HCOO)]₂ (4), the ccn^2- dianion retains a nearly planar geometry, which favors the formation of the centrosymmetric [UO₂(ccn)]₂ dimeric unit. Additional terminal ligands, either neutral (bipy = 2,2'-bipyridine) or anionic (nitrate, dibf^- = 1,3-dihydro-3-oxo-1-isobenzofuranacetate, and formate, the two latter formed in situ), complete the uranyl coordination sphere, leading in all cases to discrete, dinuclear species. Sodium(I) bonding to the carboxylate/ether O₄ site of the 1,2-pdda^2- dianion in the two complexes [UO₂Na(1,2-pdda)(OH)] (5) and [(UO₂)₂Na₂(1,2-pdda)₂(C₂O₄)] (6) results in this ligand being planar. Further lateral coordination to uranyl and sodium bonding to a uranyl oxo group allow formation of heterometallic diperiodic networks containing monoperiodic uranyl-only subunits. In the absence of Na⁺ cations, 1,2-pdda^2- adopts a conformation in which one carboxylate group is tilted out of the ligand plane in [UO₂(1,2-pdda)₂Ni(cyclam)] (7) and diaxial carboxylato bonding to nickel(II) unites uranyl-only monoperiodic subunits into a diperiodic network. The 1,3-pdda^2- ligand in [UO₂(1,3-pdda)(H₂O)] (8) is also nonplanar with one tilted carboxylate group, and the bridging bidentate nature of both carboxylate groups allows formation of a triperiodic framework in which both metal and ligand are four-coordinated nodes. While the emission spectra of complexes 1 and 5 display the vibronic progression considered typical of uranyl ion, those of complexes 2, 4, and 8 show broad emission bands which in the case of complex 4 completely replace the uranyl emission and which appear to be ligand-centered. The low energy of these broad bands can be rationalized in terms of the close association of certain ligand pairs within the structures.

Uranyl Ion Complexes of Polycarboxylates: Steps towards Isolated Photoactive Cavities

Consideration of the extensive family of known uranyl ion complexes of polycarboxylate ligands shows that there are quite numerous examples of crystalline solids containing capsular, closed oligomeric species with the potential for use as selective heterogeneous photo-oxidation catalysts. None of them have yet been assessed for this purpose, and some have obvious deficiencies, although related framework species have been shown to have the necessary luminescence, porosity and, to some degree, selectivity. Aspects of ligand design and complex composition necessary for the synthesis of uranyl ion cages with appropriate luminescence and chemical properties for use in selective photo-oxidation catalysis have been analysed in relation to the characteristics of known capsules.

Structure-Directing Effects of Coordinating Solvents, Ammonium and Phosphonium Counterions in Uranyl Ion Complexes with 1,2-, 1,3-, and 1,4-Phenylenediacetates

The three isomers 1,2-, 1,3-, and 1,4-phenylenediacetic acids (1,2-, 1,3-, and 1,4-pdaH₂) have been used to synthesize 16 uranyl ion complexes under solvo-hydrothermal conditions and in the presence of various coligands and organic counterions. The two neutral and homoleptic complexes [UO₂(1,2-pda)]·CH₃CN (1) and [UO₂(1,3-pda)] (2) crystallize as diperiodic assemblies with slightly different coordination modes of the ligands, but the same sql topology. Introduction of the coordinating solvents N-methyl-2-pyrrolidone (NMP) or N,N'-dimethylpropyleneurea (DMPU) in the uranyl coordination sphere produces the four complexes [UO₂(1,2-pda)(DMPU)] (3), [UO₂(1,3-pda)(NMP)] (4), [UO₂(1,4-pda)(NMP)] (5), and [UO₂(1,4-pda)(DMPU)] (6), which are either monoperiodic (4) or diperiodic species with the fes (3 and 5) or 3,4L13 (6) topology. The presence of dimethylammonium cations is associated with the formation of ladder-like monoperiodic polymers with the 1,2 isomer in the complexes [H₂NMe₂]₂[(UO₂)₂(1,2-pda)₃]·H₂O (7) and [H₂NMe₂]₂[(UO₂)₂(1,2-pda)₃]·3H₂O (8), while a conformational change giving the 1,3 and 1,4 isomers a pincer-like geometry favors the formation of dinuclear ring subunits assembled into daisy-chain-like monoperiodic polymers in [H₂NMe₂]₂[(UO₂)₂(1,3-pda)₃]·0.5H₂O (9), [H₂NMe₂]₂[(UO₂)₂(1,4-pda)₃] (10), and the mixed-ligand species [H₂NMe₂]₂[(UO₂)₂(1,2-pda)(1,4-pda)₂] (11). The unique complex including guanidinium cations, [C(NH₂)₃]₂[(UO₂)₂(1,2-pda)₃]·0.5H₂O·CH₃CN (12), crystallizes as a diperiodic polymer with the hcb topology. Due to differences in ligand conformations, the phosphonium-containing complexes [PPh₃Me]₂[(UO₂)₂(1,3-pda)₃] (13) and [PPh₄]₂[(UO₂)₂(1,4-pda)₃] (14) contain ladder-like and daisy-chain-like monoperiodic polymers, respectively, while only the latter geometry is found in the mixed-cation complexes [PPh₃Me][H₂NMe₂][(UO₂)₂(1,4-pda)₃]·H₂O (15) and [PPh₃Me][H₂NMe₂][(UO₂)₂(1,2-pda)(1,4-pda)₂] (16). The influence of ligand conformation and the structure-directing effects of coligands and counterions throughout the series are discussed. The uranyl emission spectra of 14 of the complexes display the usual vibronic fine structure, the peak positions being dependent on the number of equatorial donors.