Simple Sol-Gel Protein Stabilization toward Rainbow and White Lighting Devices.

Fluorescent proteins (FPs) are heralded as a paradigm of sustainable materials for photonics/optoelectronics. However, their stabilization under non-physiological environments and/or harsh operation conditions is the major challenge. Among the FP-stabilization methods, classical sol-gel is the most effective, but less versatile, as most of the proteins/enzymes are easily degraded due to the need of multi-step processes, surfactants, and mixed water/organic solvents in extreme pH. Herein, sol-gel chemistry with archetypal FPs (mGreenLantern; mCherry) is revisited, simplifying the method by one-pot, surfactant-free, and aqueous media (phosphate buffer saline pH = 7.4). The synthesis mechanism involves the direct reaction of the carboxylic groups at the FP surface with the silica precursor, generating a positively charged FP intermediate that acts as a seed for the formation of size-controlled mesoporous FP@SiO2 nanoparticles. Green-/red-emissive (single-FP component) and dual-emissive (multi-FPs component; kinetic studies not required) FP@SiO2 are prepared without affecting the FP photoluminescence and stabilities (>6 months) under dry storage and organic solvent suspensions. Finally, FP@SiO2 color filters are applied to rainbow and white bio-hybrid light-emitting diodes featuring up to 15-fold enhanced stabilities without reducing luminous efficacy compared to references with native FPs. Overall, an easy, versatile, and effective FP-stabilization method is demonstrated in FP@SiO2 toward sustainable protein lighting.

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.

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.

Flexible Aliphatic Diammonioacetates as Zwitterionic Ligands in UO22+ Complexes: Diverse Topologies and Interpenetrated Structures.

N,N,N',N'-Tetramethylethane-1,2-diammonioacetate (L1) and N,N,N',N'-tetramethylpropane-1,3-diammonioacetate (L2) are two flexible zwitterionic dicarboxylates which have been used as ligands for the uranyl ion, 12 complexes having been obtained from their coupling to diverse anions, mostly anionic polycarboxylates, or oxo, hydroxo and chlorido donors. The protonated zwitterion is a simple counterion in [H2L1][UO2(2,6-pydc)2] (1), where 2,6-pydc2- is 2,6-pyridinedicarboxylate, but it is deprotonated and coordinated in all the other complexes. [(UO2)2(L2)(2,4-pydcH)4] (2), where 2,4-pydc2- is 2,4-pyridinedicarboxylate, is a discrete, binuclear complex due to the terminal nature of the partially deprotonated anionic ligands. [(UO2)2(L1)(ipht)2]·4H2O (3) and [(UO2)2(L1)(pda)2] (4), where ipht2- and pda2- are isophthalate and 1,4-phenylenediacetate, are monoperiodic coordination polymers in which central L1 bridges connect two lateral strands. Oxalate anions (ox2-) generated in situ give [(UO2)2(L1)(ox)2] (5) a diperiodic network with the hcb topology. [(UO2)2(L2)(ipht)2]·H2O (6) differs from 3 in being a diperiodic network with the V2O5 topological type. [(UO2)2(L1)(2,5-pydc)2]·4H2O (7), where 2,5-pydc2- is 2,5-pyridinedicarboxylate, is a hcb network with a square-wave profile, while [(UO2)2(L1)(dnhpa)2] (8), where dnhpa2- is 3,5-dinitro-2-hydroxyphenoxyacetate, formed in situ from 1,2-phenylenedioxydiacetic acid, has the same topology but a strongly corrugated shape leading to interdigitation of layers. (2R,3R,4S,5S)-Tetrahydrofurantetracarboxylic acid (thftcH4) is only partially deprotonated in [(UO2)3(L1)(thftcH)2(H2O)] (9), which crystallizes as a diperiodic polymer with the fes topology. [(UO2)2Cl2(L1)3][(UO2Cl3)2(L1)] (10) is an ionic compound in which discrete, binuclear anions cross the cells of the cationic hcb network. 2,5-Thiophenediacetate (tdc2-) is peculiar in promoting self-sorting of the ligands in the ionic complex [(UO2)5(L1)7(tdc)(H2O)][(UO2)2(tdc)3]4·CH3CN·12H2O (11), which is the first example of heterointerpenetration in uranyl chemistry, involving a triperiodic, cationic framework and diperiodic, anionic hcb networks. Finally, [(UO2)7(O)3(OH)4.3Cl2.7(L2)2]Cl·7H2O (12) crystallizes as a 2-fold interpenetrated, triperiodic framework in which chlorouranate undulating monoperiodic subunits are bridged by the L2 ligands. Complexes 1, 2, 3, and 7 are emissive with photoluminescence quantum yields in the range of 8-24%, and their solid-state emission spectra show the usual dependence on number and nature of donor atoms.

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, cbtc4- = cis,trans,cis-1,2,3,4-cyclobutanetetracarboxylate) is a discrete, dinuclear ring-shaped complex with a central cbtc4- 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-pda2- = 1,3-phenylenediacetate) is a daisy chain and [UO2(pL1)(pdda)]3·10H2O (6, pdda2- = 1,2-phenylenedioxydiacetate) is a double-stranded, ribbon-like chain. Both [UO2(pL1)(pht)]·5H2O (7, pht2- = 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-chdc2- = cis/trans-1,3-cyclohexanedicarboxylate) and [UO2(pL1)(t-1,4-chdc)]·1.5H2O (10, t-1,4-chdc2- = 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-pda2- = 1,2-phenylenediacetate) crystallize as diperiodic networks with hcb topology, and they display threefold parallel interpenetration. [HL2][(UO2)3(L2)(adc)3]Br (13, adc2- = 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, kpim2- = 4-ketopimelate) is a three-periodic framework with pL1 molecules pillaring fes diperiodic subunits, whereas [(UO2)2(L2)2(t-1,4-chdc)](NO3)1.7Br0.3·6H2O (15), the only cationic complex in the series, is a triperiodic framework with dmc topology and t-1,4-chdc2- anions pillaring fes diperiodic subunits. Solid-state emission spectra and photoluminescence quantum yields are reported for all complexes.

The Role of a Confined Space on the Reactivity and Emission Properties of Copper(I) Clusters.

Metal clusters have gained a lot of interest for their remarkable photoluminescence and catalytic properties. However, a major drawback of such materials is their poor stability in air and humidity conditions. Herein we describe a versatile method to synthesize luminescent Cu(I) clusters inside the pores of zeolites, using a sublimation technique with the help of high vacuum and high temperature. The porous materials play an essential role as a protecting media against the undesirable and easy oxidation of Cu(I). The obtained clusters show fascinating luminescence properties, and their reactivity can be triggered by insertion in the pores of organic monodentate ligands such as pyridine or triphenylphosphine. The coordinating ligands can lead to the formation of Cu(I) complexes with completely different emission properties. In the case of pyridine, the final compound was characterized and identified as a cubane-like structure. A thermochromism effect is also observed, featuring, for instance, a hypsochromic effect for a phosphine derivative at 77K. The stability of the encapsulated systems in zeolites is rather enthralling: they are stable and emissive even after several months in the air.

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.

Zero-, mono- and diperiodic uranyl ion complexes with the diphenate dianion: influences of transition metal ion coordination and differential UVI chelation.

Diphenic acid (H2dip) has been used to synthesize nine homo- or heterometallic uranyl ion complexes under solvo-hydrothermal conditions. The diphenate ligand dip2- adopts different coordination modes, mixtures of κ2-O,O'-chelation by individual carboxylate groups, chelation involving both carboxylate groups, and bridging, resulting in different associations of the cations present. [UO2(dip)] (1), [UO2(dip)(bipy)] (2), and [UO2(dip)(phen)] (3) crystallize as monoperiodic coordination polymers, complex 1 with the bridging and both chelation modes of the ligand, and 2 and 3 with only the bis-κ2-O,O'-chelated mode and further chelation by 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen). The two isomorphous complexes [H2NMe2]2[(UO2)2(dip)3] (4) and [(UO2)2Ag2(dip)3(H2O)(CH3CN)] (5) display ladder-like monoperiodic arrangements with the hydrogen bonded H2NMe2+ or carboxylate-bound, decorating Ag+ cations occupying similar positions within the chains. [Ni(R,S-Me6cyclam)(H2O)2][UO2(dip)2] (6) contains a discrete dianionic mononuclear species, while [(UO2)2(dip)2(Hdip)2Ni(cyclam)]·2H2O·2CH3CN (7) crystallizes as a monoperiodic, heterometallic polymer, with further formation of layers through reciprocal hydrogen bonding of the carboxylic acid groups. A discrete dinuclear dianionic complex is present in [Cu(R,S-Me6cyclam)][UO2(dip)(NO3)]2 (8), which crystallizes together with [(UO2)3(dip)4Cu(R,S-Me6cyclam)(H2O)2]·6H2O (9), a diperiodic assembly in which uranyl-containing dimeric units are assembled in chains through diaxial carboxylate coordination of Cu(R,S-Me6cyclam)2+ cations, with further bridging by uranyl cations generating a network with the fes topology. The uranyl emission spectra of complexes 3, 4 and 5 show the usual vibronic fine structure, while uranyl emission in 7 is largely quenched.

The sulfonate group as a ligand: a fine balance between hydrogen bonding and metal ion coordination in uranyl ion complexes.

Nine uranyl ion complexes have been synthesized using two kinds of sulfonate-containing ligands, i.e. 2-, 3- and 4-sulfobenzoic acids (2-, 3- and 4-SBH2), which include additional carboxylic donors, and p-sulfonatocalix[4]arene (H8C4S), with additional phenolic groups, and [Ni(cyclam)]2+, [Cu(R,S-Me6cyclam)]2+ or PPh4+ as counterions. [Ni(cyclam)][UO2(4-SB)2(H2O)2]·2CH3CN (1) and [Ni(cyclam)][UO2(3-SB)2(H2O)2] (2) are molecular species in which only the carboxylate groups are coordinated to uranyl, the sulfonate groups being essentially hydrogen bond acceptors. In contrast, uranyl κ1-O(S);κ1-O(C)-chelation is found in the four complexes involving 2-SB2-, different bridging interactions producing diverse geometries. [UO2(2-SB)2Ni(cyclam)]·H2O (3) crystallizes as a two-dimensional (2D) assembly with fes topology, in which uranyl ion dimeric subunits are bridged by six-coordinate NiII cations. Complexes [UO2(2-SB)2Cu(R,S-Me6cyclam)]2·2H2O (4) and [(UO2)2(2-SB)2(C2O4)Cu(R,S-Me6cyclam)] (5), obtained together from the same solution, are a molecular tetranuclear complex and a 2D species with fes topology, respectively, depending on the coordination number, 5 or 6, of the CuII cation. The complex [PPh4]2[(UO2)2(2-SB)3(H2O)]·H2O (6) is a one-dimensional (1D), ribbon-like coordination polymer with a layered packing of alternate cationic and anionic sheets. No heterometallic complex was obtained with H8C4S, but the copper-only compound [{Cu(R,S-Me6cyclam)}5(H3C4S)2]·17H2O (7) displays mixed coordination/hydrogen bonding association of the copper azamacrocycle complex with the phenolic groups. The complexes [PPh4]5[UO2(H4C4S)(H2O)4][UO2(H3C4S)(H2O)4]·14H2O (8) and [PPh4]3[UO2(H3C4S)(H2O)3]·9H2O (9) were crystallized from the same solution and are a molecular complex and a 1D polymer, respectively, with monodentate sulfonate coordination to uranyl, while [PPh4]2[UO2(H4C4S)(H2O)3]·11H2O (10) is also a 1D polymer. The anionic complexes in the last three complexes form layers (9) or double layers (8 and 10) separated from one another by hydrophobic layers of PPh4+ cations. The balance between coordination and hydrogen bonding interactions with the macrocyclic ligands provides an indication of the energy of the sulfonate coordinate bond. Complex 6 is the only luminescent species in this series, albeit with a low quantum yield of 3%, and its emission spectrum is typical of a uranyl complex with five equatorial donors.

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.

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

Nine uranyl ion complexes were synthesized under (solvo-)hydrothermal conditions using α,ω-dicarboxylic acids HOOC-(CH2) n-2-COOH (H2C n, n = 6-9) and diverse counterions. Complexes [PPh4][UO2(C6)(NO3)] (1) and [PPh4][UO2(C8)(NO3)] (2) contain zigzag one-dimensional (1D) chains, with further polymerization being prevented by the terminal nitrate ligands. [PPh3Me][UO2(C7)(HC7)] (3) crystallizes as a 1D polymer with a curved section, with hydrogen bonding of the uncomplexed carboxylic groups giving rise to formation of 3-fold interpenetrated two-dimensional (2D) networks. [PPh4][H2NMe2][(UO2)2(C7)3] (4) and [PPh3Me]2[(UO2)2(C8)3] (5) contain 1D chains, either ladder-like or containing doubly bridged dimers, while [PPh3Me]2[(UO2)2(C9)3]·2H2O (6) displays interdigitated, strongly corrugated honeycomb 2D nets. Ladder-like 1D polymers in [Cu( R,S-Me6cyclam)][(UO2)2(C7)2(C2O4)]·4H2O (7) are associated into layers by the hydrogen bonded counterions, whereas the [Ni(cyclam)]2+ moieties are part of the 2D polymeric arrangement in [(UO2)2(C7)2(HC7)2Ni(cyclam)]·2H2O (8) because of axial coordination of the nickel(II) center, with hydrogen bonding mediated by water molecules generating a three-dimensional (3D) net. [(UO2)2K2(C7)3(H2O)]·0.5H2O (9) contains convoluted uranyl dicarboxylate 2D subunits, which generate a 3D framework through 2D → 3D parallel polycatenation similar to that previously found in [NH4]2[(UO2)2(C7)3]·2H2O; further linking of these subunits is provided by bonding of the potassium cations to carboxylate and uranyl oxido groups. The solid-state emission spectra of complexes 1-6 and 9 display maxima positions typical of hexacoordinated uranyl carboxylate complexes, but uranyl luminescence is quenched in 7. A solid-state photoluminescence quantum yield of 11.5% has been measured for complex 1, while those for compounds 3-6 and 9 are in the range of 2.0-3.5%.

Luminescence of Amphiphilic PtII Complexes Controlled by Confinement.

The formation of hybrid silica-based systems to study the effect of the confinement on the emission properties of self-assembled platinum(II) complexes is reported. The complexes behave as surfactants since they possess a hydrophobic moiety and, on the ancillary ligand, a relatively long hydrophilic chain terminated with a positively charged group. The compounds, soluble in water, self-assemble, even at very low concentration, in supramolecular structures which display an orange luminescence. The properties of the assemblies have been studied in detail and in order to stabilize these supramolecular architectures and to enhance their emission properties hybrid silica porous nanoparticles have been prepared. In particular the PtII complexes have been employed as co-surfactant for the template formation of mesoporous silica nanoparticles (MSNs) using a sol gel synthesis. Interestingly, upon encapsulation in the silica pores, the platinum aggregates exhibit an emission profile similar in energy to the complexes assembled in solution, but the photoluminescence quantum yields of the hybrid systems are significantly higher (up to 45 %), and the excited state lifetimes much longer than those recorded in solution. Such enhancement of the photophysical properties together with the possibility to process the hybrid silica nanomaterials can pave the way to new type of emitters.

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.

Counterion-Controlled Formation of an Octanuclear Uranyl Cage with cis-1,2-Cyclohexanedicarboxylate Ligands.

cis-1,2-Cyclohexanedicarboxylic acid ( c-chdcH2) was reacted with uranyl nitrate under (solvo-)hydrothermal conditions in the presence of different possible counterions. Two neutral complexes of 1:1 stoichiometry were obtained, [UO2( c-chdc)(DMF)] (1) and [UO2( c-chdc)(H2O)] (2), which crystallize as two-dimensional coordination polymers and do not include the additional cations present in solution. In contrast, the complex [NH4][PPh4][(UO2)8( c-chdc)9(H2O)6]·3H2O (3) crystallized in the presence of PPh4Br, ammonium cations being generated in situ from acetonitrile hydrolysis. This complex of 8:9 uranium:ligand stoichiometry contains an octanuclear anionic cage of D3 symmetry with a pseudo-cubic arrangement of uranium atoms. The ammonium cation is held within the cage through four hydrogen bonds with uranyl oxo groups directed inward. This cage complex is luminescent, although with a low quantum yield of 0.06, indicating limited potential as a photo-oxidant of included species.