Solvo-hydrothermal Conditions Research Articles

1,1ʹ-Dimethyl-4,4ʹ-bipyridinium as a multivalent structure-directing counterion to anionic uranyl ion polycarboxylate complexes

Seven uranyl ion complexes with polycarboxylates have been synthesized under solvo-hydrothermal conditions and in the presence of 1,1ʹ-dimethyl-4,4ʹ-bipyridinium (Me2bipy2+) as structure-directing counterion. Two complexes were obtained with phthalate (pht2–), [Me2bipy]2[(UO2)4(pht)4(O)2] (1), which is a discrete, bis(μ3-oxo-bridged) tetranuclear species, and {[Me2bipy][(UO2)3(pht)4(H2O)]}n (2), which crystallizes as a monoperiodic coordination polymer. The complex obtained with citric acid (H4cit), {[Me2bipy][UO2(Hcit)]2·H2O}n (3), assumes a well-known monoperiodic form. {[Me2bipy][(UO2)2(Hthftc)2]}n (4), obtained from tetrahydrofurantetracarboxylic acid (H4thftc), is also a monoperiodic polymer further assembled into layers through hydrogen bonding, the packing defining channels containing columns of stacked counterions. The previously reported {[Me2bipy][(UO2)2(tdc)3]}n (5), where tdc2– is 2,5-thiophenedicarboxylate, is a diperiodic hcb network, with the counterions crossing the hexanuclear rings. One experiment with pimelate (pim2–) gave the two complexes {[Me2bipy][(UO2)2(pim)3]}n (6) and {[Me2bipy][(UO2)4(pim)5(DMA)2]}n (7) (DMA = N,N-dimethylacetamide). Both 6 and 7 are diperiodic assemblies, but while 6 has the KIa topology previously found in other uranyl ion complexes with elongated dicarboxylate ligands, 7 is a very intricate and thick assembly with a packing displaying interdigitation. The weak interactions formed by the counterions are discussed through examination of Hirshfeld surfaces.

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 (ipht2-) and 1,2-, 1,3-, or 1,4-phenylenediacetate (1,2-, 1,3-, and 1,4-pda2-), 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.

(R,R)-Tartrate as a polytopic ligand for UO22+: Mono- and diperiodic coordination polymers including di- and tetranuclear subunits

(R,R)-Tartaric acid (H4tart) has been reacted with uranyl nitrate hexahydrate under solvo-hydrothermal conditions, in the presence of either [Ni(R,S-Me6cyclam)]2+ (R,S-Me6cyclam = 7(R),14(S)-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane), quinH+ (quinuclidinium), or [Ni(bipy)3]2+ (bipy = 2,2ʹ-bipyridine), to give three complexes characterized by their crystal structure. [H2NMe2]2[(UO2)2(Htart)2(HCOO)2Ni(R,S-Me6cyclam)]⋅2H2O (1) crystallizes as a monoperiodic coordination polymer in which dimeric [UO2(Htart)]22– subunits are linked by nickel(II) cations. The structure of the dimers matches that expected from solution experiments but not previously found in the solid state. Both [Hquin][(UO2)2(tart)(CH3COO)] (2) and [Ni(bipy)3][(UO2)2(tart)(CH3COO)]2 (3) crystallize as diperiodic networks based on tetranuclear [(UO2)2(tart)(CH3COO)]22– subunits which contain a central U2O2 ring involving μ2-bridging alkoxide groups. Further chelation of the two lateral uranyl cations by the carboxylate groups of adjacent subunits yields a sql-type network. Due to the different bulk of the counterions, the layers are quasi-planar in 2 and corrugated in 3. Comparison of these polynuclear subunits with those formed by the related ligands citrate, R,S-malate and R-citramalate shows that while the dimeric form is common to all, the tetranuclear subunit is specific to the tartrate ligand.

Nanotubule inclusion in the channels formed by a six-fold interpenetrated, triperiodic framework.

When reacted together with uranyl ions under solvo-hydrothermal conditions, a bis(pyridiniumcarboxylate) zwitterion (L) and tricarballylic acid (H3tca) give the complex [NH4]2[UO2(L)2][UO2(tca)]4·2H2O (1). The two ligands are segregated into different units, an anionic nanotubule for tca3- and a six-fold interpenetrated cationic framework with lvt topology for L. The entangled framework defines large channels which contain the square-profile nanotubules. Complex 1 has a photoluminescence quantum yield of 19% and its emission spectrum shows the superposition of the signals due to the two independent species.

Anionic uranyl ion complexes with pyrazinetetracarboxylate: Influence of structure-directing cations

Pyrazine-2,3,5,6-tetracarboxylic acid (H4PZTC) has been used to synthesize three uranyl ion complexes under solvo-hydrothermal conditions and in the presence of additional cations as structure-directing agents. The complex [C(NH2)3]2[UO2(PZTC)]⋅2H2O (1) displays double ONO-chelation of uranyl, resulting in the formation of a monoperiodic coordination polymer, further association being provided by guanidinium and water hydrogen bonding. The PZTC4– ligand in [Co(en)3][UO2(PZTC)](NO3)⋅H2O (2) is bound to three uranyl cations, one of them ONO-chelated and the others bound to monodentate carboxylate donors, and the polymer formed is triperiodic with the ths topology. The ONO sites in the heterometallic complex [UO2Ag2(PZTC)] (3) are occupied by Ag+ cations, further carboxylate bonding to uranyl and Ag+ cations, as well as oxo bonding of uranyl to Ag+, resulting in the formation of an intricate triperiodic framework in which uranyl cations and PZTC4– alone give a triperiodic polymer with the lvt topology displaying double interpenetration, the Ag+ cations connecting the two networks into a single assembly.

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 NiII 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-chdc2- is cis-1,2-cyclohexanedicarboxylate and tdc2- 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 bdc2- 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 tca3- is tricarballylate. [(UO2)2(1,2-pda) (1,2-pdaH)Ni(tpyc)2(NO3)]·CH3CN (5), where 1,2-pda2- 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 (ox2-) gives [(UO2)2(ox)2Ni(tpyc)2] (6), a monoperiodic polymer containing smaller U4Ni rings, while 1,2,3-benzenetricarboxylate (1,2,3-btc3-) and citrate (citH3-) 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 btc4- and cbtc4- 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 ndc2- 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-chdc2- is trans-R,R-1,2-cyclohexanedicarboxylate, the heavily puckered sheets being interlocked. 1,3-Phenylenediacetate (1,3-pda2-) 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 (nta3-) in [(UO2)2(nta)2Ni2(tpyc)2] (14), where NiII is found in Ni(tpyc)2 units as well as in Ni(nta)24- moieties which both act as 4-coordinated nodes.

Multiple aspects of chirality in coordination polymers formed by the uranyl ion with (1R,3S)-(+)-camphorate ligands

Following previous work on complexes of the anions of (1R,3S)-(+)-camphoric acid (H2cam) with the uranyl cation, three novel species have been synthesized under solvo-hydrothermal conditions. [UO2(Hcam)2(4,4ʹ-bipy)] (1), where 4,4ʹ-bipy is 4,4ʹ-bipyridine, crystallizes as a monoperiodic polymer with bridging 4,4ʹ-bipy molecules and chelating, terminal Hcam– anions, hydrogen bonding between carboxylic and carboxylate groups in adjacent chains giving diperiodic networks. [UO2(cam)(2,2ʹ-bipy)] (2), where 2,2ʹ-bipy is 2,2ʹ-bipyridine, crystallizes also as a monoperiodic polymer, but bis-chelating cam2– anions are here bridging and the chelating 2,2ʹ-bipy ligands induce chirality at the uranium atoms; the chains are helical, left- or right-handed depending on the chirality of the associated uranium centres. [Zn(phen)3][(UO2)2(cam)3] (3), where phen is 1,10-phenanthroline, is an anionic diperiodic network with hcb topology displaying a grooved shape. In all three instances, the enantiomeric purity of the camphorate ligands does not produce significant enantioselectivity in regard to other aspects of the structural chirality.

Lead(II) complexes with Kemp’s tricarboxylate: Can lone pair activity be discerned?

Kemp’s triacid (H3kta; cis,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid) has been used to synthesize three lead(II) complexes under solvo-hydrothermal conditions. [Pb3(kta)Cl3] (1) and [Pb3(H3kta)(kta)2] (2) are both diperiodic coordination polymers displaying hydrophobic surfaces with protruding methyl groups, complex 2 being isomorphous with an SrII complex previously reported. In contrast, [Pb(Hkta)(phen)] (3), where phen is 1,10-phenanthroline, is a monoperiodic, helical coordination polymer. In all cases, PbII cations are in seven- or eight-coordinate environments of predominantly hemidirected nature. The possible effects of the PbII valence shell lone pair are discussed in terms of coordination geometry and Pb⋅⋅⋅H weak interactions as revealed on Hirshfeld surfaces. Only in complex 1 is a short Pb⋅⋅⋅H contact at 2.84 Å possibly indicative of appreciable basicity of the metal ion. All three complexes show similar weak luminescence, apparently independent of the nature of the ligands.

Contrasting Networks and Entanglements in Uranyl Ion Complexes with Adipic and trans,trans-Muconic Acids.

Adipic (hexane-1,6-dicarboxylic, adpH2) and trans,trans-muconic (trans,trans-hexa-2,4-diene-1,6-dicarboxylic, mucH2) acids have been reacted with uranyl cations under solvo-hydrothermal conditions, yielding nine homo- or heterometallic complexes displaying in their crystal structure the effects of the different flexibility of the ligands. The complexes [PPh4]2[(UO2)2(adp)3] (1) and [Ni(bipy)3][(UO2)2(muc)3]·5H2O (2), where bipy is 2,2'-bipyridine, crystallize as diperiodic networks with the hcb topology, the layers being strongly puckered or quasiplanar, respectively. Whereas [(UO2)2(adp)3Ni(cyclam)]·2H2O (3), where cyclam is 1,4,8,11-tetraazacyclotetradecane, crystallizes as a diperiodic network, [(UO2)2(muc)3Ni(cyclam)]·2H2O (4) is a triperiodic framework in which the NiII cations are introduced as pillars within a uranyl-muc2- framework with the mog topology. [UO2(adp)(HCOO)2Cu(R,S-Me6cyclam)]·2H2O (5), where R,S-Me6cyclam is 7(R),14(S)-5,5,7,12,12,14-hexamethylcyclam, is a diperiodic assembly with the sql topology, and it crystallizes together with [H2NMe2]2[(UO2)2(adp)3] (6), a highly corrugated hcb network with a square-wave profile, which displays 3-fold parallel interpenetration. In contrast, [(UO2)3(muc)2(O)2Cu(R,S-Me6cyclam)] (7) is a diperiodic assembly containing hexanuclear, μ3-oxido-bridged secondary building units which are the nodes of a network with the hxl topology. The two related complexes [PPh3Me]2[(UO2)2(adp)3]·4H2O (8) and [PPh3Me]2[(UO2)2(muc)3]·H2O (9) crystallize as hcb networks, but their different shapes, undulated or quasiplanar, respectively, result in different entanglements, 2-fold parallel interpenetration in 8 and 2-fold inclined 2D → 3D polycatenation in 9.

2,5-Thiophenedicarboxylate: An Interpenetration-Inducing Ligand in Uranyl Chemistry.

Seven uranyl ion complexes have been crystallized under solvo-hydrothermal conditions from 2,5-thiophenedicarboxylic acid (tdcH2) and diverse additional, structure-directing species. [UO2(tdc)(DMF)] (1) is a two-stranded monoperiodic coordination polymer, while [PPh3Me][UO2(tdc)(HCOO)] (2) is a simple chain with terminal formate coligands. Although it is also monoperiodic, [C(NH2)3][H2NMe2]2[(UO2)3(tdc)4(HCOO)] (3) displays an alternation of tetra- and hexanuclear rings. Two-stranded subunits are bridged by oxo-coordinated NiII cations to form a diperiodic network in [UO2(tdc)2Ni(cyclam)] (4), but a homometallic sql diperiodic assembly is built in [Cu(R,S-Me6cyclam)(H2O)][UO2(tdc)2]·H2O (5), to which the counterion is hydrogen bonded only. Diperiodic networks with the hcb topology are formed in both [Zn(phen)3][(UO2)2(tdc)3]·2H2O·3CH3CN (6) and [PPh4]2[(UO2)2(tdc)3]·2H2O (7). The slightly undulating layers in 6 are crossed by oblique columns of weakly interacting counterions in polythreading-like fashion. In contrast, the larger curvature in 7 allows for three-fold, parallel 2D interpenetration to occur. These results are compared with previously reported cases of interpenetration and polycatenation in the uranyl-tdc2- system.

Contrasting Structure-Directing Effects in the Uranyl–Phthalate/Isophthalate Isomer Systems

Reaction of uranyl cations with phthalic (H2pht) or isophthalic (H2ipht) acids under solvohydrothermal conditions was performed in the presence of 3d-block metal cations associated with chelating n...

Cavity Formation in Uranyl Ion Complexes with Kemp's Tricarboxylate: Grooved Diperiodic Nets and Polynuclear Cages.

Kemp's triacid (cis,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid, H3kta) was reacted with uranyl nitrate under solvo-hydrothermal conditions in the presence of diverse counterions or additional metal cations to give eight zero- or diperiodic complexes. All the coordination polymers in the series, [PPh3Me][UO2(kta)]·0.5H2O (1), [PPh4][UO2(kta)] (2), [C(NH2)3][UO2(kta)] (3), [Cd(bipy)3][UO2(kta)]2 (4), and [Zn(phen)3][UO2(kta)]2·2H2O (5) (bipy = 2,2'-bipyridine, phen = 1,10-phenanthroline) crystallize as networks with the hcb topology, the ligand being in the chair conformation with the three carboxylate groups equatorial, except in 3, in which the axial/diequatorial boat conformation is present. Various degrees of corrugation and different arrangements of neighboring layers are observed depending on the counterion, with complexes 4 and 5, in particular, displaying cavities containing the bulky cations. [Co(en)3]2[(UO2)2(kta)(Hkta)2]2·2NMP·10H2O (6) (en = 1,2-ethanediamine; NMP = N-methyl-2-pyrrolidone) contains a metallatricyclic, tetranuclear anionic species, displaying two clefts in which the cations are held by extensive hydrogen bonding, and with the ligands in both triaxial chair and axial/diequatorial boat conformations. [(UO2)3Pb(kta)2(Hkta)(H2O)]2·1.5THF (7) (THF = tetrahydrofuran) and [(UO2)2Pb2(kta)2(Hkta)(NMP)]2 (8) are two heterometallic cage compounds containing only the convergent, triaxial chair form of the ligand, which have the same topology in spite of the different U/Pb ratio. These complexes are compared to previous ones also involving Kemp's triacid anions, and the roles of ligand conformation and of counterions in the formation of cavities, either in cage-like species or as grooves in diperiodic networks, is discussed.

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 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.

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 ccn2- 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-pdda2- 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-pdda2- 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-pdda2- 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.

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.

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

Fourteen uranyl ion complexes have been obtained from reaction of 1,2-, 1,3-, or 1,4-phenylenediacetic acids (1,2-, 1,3-, or 1,4-H2PDA) with uranyl nitrate under solvo-hydrothermal conditions and in the presence of diverse additional metal ions and/or N-donor chelating or macrocyclic species. The complexes [UO2(1,2-PDA)(bipy)]·CH3CN (1), [UO2(1,2-PDA)(phen)] (2), [UO2(1,3-PDA)(bipy)] (3), and [UO2(1,3-PDA)(phen)] (4), where bipy = 2,2′-bipyridine and phen = 1,10-phenanthroline, crystallize as simple monoperiodic (1D) coordination polymers with slightly variable geometry and mode of association through weak interactions. Complex 5, [H2-2.2.2][(UO2)2(1,2-PDA)3]·CH3CN, containing diprotonated [2.2.2]cryptand, crystallizes as a ladder-like 1D polymer, while [NH4]6[Ni(H2O)6]2[(UO2)4(1,2-PDA)6]2[(UO2)4(1,2-PDA)5(H2O)4] (6) contains both a heavily corrugated 1D subunit and a discrete, tetranuclear anionic complex. The three complexes [Cu(bipy)2(NO3)][UO2(1,2-PDA)(NO3)] (7), [Ag(bipy)2][UO2(1,2-PDA)(NO3)] (8), an...

Favoring Framework Formation through Structure-Directing Effects in Uranyl Ion Complexes with 1,2,3,4-(Cyclo)butanetetracarboxylate Ligands

Six uranyl ion complexes with 1,2,3,4-cyclobutanetetracarboxylic acid (H4CBTC) and one with 1,2,3,4-butanetetracarboxylic acid (H4BTC) have been obtained under solvo-hydrothermal conditions in the presence of diverse, organic or metallic counterions. The different conformations found for the cyclic ligand (cis,trans,cis or trans,trans,trans in most cases, with one instance of cis,trans,trans), the diverse coordination modes adopted, and the presence of additional metal cations in some cases result in variations in dimensionality and topology of the complexes formed. Two complexes involve protonated azamacrocycles as counterions, [R,S-Me6cyclamH2][UO2(CBTC)] (1) and [cyclamH4][UO2(CBTC)]2 (2), where cyclam = 1,4,8,11-tetra-azacyclotetradecane and R,S-Me6cyclam = 7(R),14(S)-5,5,7,12,12,14-hexamethylcyclam, which crystallize as a one-dimensional (1D) ribbon-like coordination polymer and a two-dimensional (2D) network with sql topology, respectively, the counterions providing additional hydrogen bonding conne...

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

Reaction of 1,2-, 1,3-, or 1,4-phenylenediacetic acids (1,2-, 1,3-, or 1,4-H2PDA) with uranyl ions under solvo-hydrothermal conditions and in the presence of [M(L) n] q+ cations, in which M = transition metal cation, L = 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen), n = 2 or 3, and q = 1 or 2, gave 10 complexes which have been crystallographically characterized. The diacetate ligands are bis-chelating and the uranyl cations are tris-chelated in all cases. [UO2(1,2-PDA)2Zn(phen)2]·2H2O (1) and [UO2(1,4-PDA)2Mn(bipy)2]·H2O (2) are heterometallic, neutral one-dimensional (1D) coordination polymers in which the carboxylate-coordinated 3d block metal cation is either decorating only (1) or participates in polymer building (2). [Zn(phen)3][(UO2)2(1,3-PDA)3] (3) and [Ni(phen)3][(UO2)2(1,4-PDA)3]·H2O (4), with separate counterions, crystallize as anionic two-dimensional (2D) networks, as does [Cu(bipy)2][H2NMe2][(UO2)2(1,4-PDA)3] (5), which displays parallel 2D interpenetration. The complex [Zn(phen)3][(UO2)2(1,2-PDA)3]·7H2O (6) crystallizes as a ladderlike, slightly inflated ribbon. The same topology is found in [Zn(bipy)3][(UO2)2(1,3-PDA)3] (7), but the larger separation between coordination sites and the coexistence of curved and divergent ligand conformations produce a tubelike assembly. An analogous but more regular and spacious tubular geometry is found in [M(bipy)3][(UO2)2(1,4-PDA)3], with M = Co (8) or Ni (9), and {Λ-[Ru(bipy)3]}[(UO2)2(1,4-PDA)3] (10). The disordered counterions in 8 and 9 are replaced by well-ordered, enantiomerically pure chiral counterions in 10. The tubular assemblies formed in 7-10 are characterized by an oblong section and the presence of gaps in the walls, which enable the inclusion of two rows of counterions in the cavity.

Chiral Discrete and Polymeric Uranyl Ion Complexes with (1 R,3 S)-(+)-Camphorate Ligands: Counterion-Dependent Formation of a Hexanuclear Cage.

Reaction of (1 R,3 S)-(+)-camphoric acid (H2cam) with uranyl ions under solvo-hydrothermal conditions and in the presence of bulky countercations gave five chiral complexes of varying dimensionality. [Cu( R,S-Me6cyclam)][UO2(Hcam)2(HCOO)2] (1) and [Ni( R,S-Me6cyclam)][UO2(cam)(HCOO)2] (2), in which the formate coligand is formed in situ, involve very similar countercations, but 1 is a discrete, mononuclear complex, whereas 2 crystallizes as a one-dimensional (1D) coordination polymer, and NH-bond donation by the macrocyclic ligand of the countercation complexes is present in both. [Co(en)3][(UO2)4(cam)( R,R-tart)2(OH)]·3H2O (3), in which en is ethylenediamine and H4 R,R-tart is R,R-tartaric acid, contains three enantiomerically pure chiral species, and it displays a two-dimensional (2D) arrangement, with the countercation again involved in NH-bond donation. While [PPh4][UO2(cam)(NO3)] (4) is a 1D polymer, [PPh3Me]3[NH4]3[(UO2)6(cam)9] (5) is a discrete, homochiral, and homoleptic hexanuclear cage with C3 point symmetry and a trigonal prismatic arrangement of the uranium atoms. This cage differs from the octanuclear, pseudocubic uranyl camphorate species previously described, thus providing an example of modulation of the cage size through variation of the structure-directing counterions. The cage in 5 is closely associated with three PPh3Me+ cations, two of them outside and with their methyl group directed toward the prism basis center, and one inside the cage cavity. While complex 5 is nonluminescent, complexes 1 and 4 have emission spectra in the solid state typical of equatorially hexacoordinated uranyl complexes. Solid-state photoluminescence quantum yields of 2 and 23% have been measured for complexes 1 and 4, respectively.

Closed Uranyl-Dicarboxylate Oligomers: A Tetranuclear Metallatricycle with Uranyl Bridgeheads and 1,3-Adamantanediacetate Linkers.

In the presence of NH4+ and either PPh4+ or PPh3Me+ cations, 1,3-adamantanediacetic acid (H2ADA) reacts with uranyl ions under solvo-hydrothermal conditions to give the complexes [NH4]2[PPh4]2[(UO2)4(ADA)6] (1) and [NH4]2[PPh3Me]2[(UO2)4(ADA)6] (2), both of which contain a tetranuclear metallatricycle built from two 2:2 rings including convergent ligands, linked by two additional ligands in an extended conformation defining a third, larger ring. While the ammonium cations are closely associated with the 2:2 rings through triple hydrogen bonding, the large PPh4+ or PPh3Me+ cations are more loosely bound to each of the two faces of the larger ring. In contrast, the complex [H2NMe2][PPh3Me][(UO2)2(ADA)3]·H2O (3), in which dimethylammonium replaces ammonium cations, crystallizes as a two-dimensional network with honeycomb {63} topology, albeit with very distorted, elongated hexagonal cells. These and previous results show that both NH4+ and PPh4+ or PPh3Me+ cations are essential to the formation of the metallatricycle. The role of the flexibility imparted to ADA2- by the acetate arms, in comparison to the more rigid 1,3-adamantanedicarboxylate (ADC2-), is also discussed. All three complexes are luminescent, with quantum yields of 0.06, 0.06, and 0.09 for 1-3, respectively. The vibronic fine structure apparent on the emission spectra gives peak positions typical of species in which the uranyl ion is chelated by three carboxylate groups.