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

Abstract

Nine uranyl ion complexes were synthesized under (solvo-)hydrothermal conditions using α,ωdicarboxylic acids HOOC-(CH2)n-2-COOH (H2Cn, n = 6-9) and diverse counterions. Complexes [PPh4][UO2(C6)(NO3)] (1) and [PPh4][UO2(C8)(NO3)] (2) contain zigzag one-dimensional (1D) chains, further polymerization being prevented by the terminal nitrate ligands. [PPh3Me][UO2(C7)(HC7)] (3) crystallizes as a 1D polymer with a curved section, hydrogen bonding of the uncomplexed carboxylic groups giving rise to formation of threefold interpenetrated two-dimensional (2D) networks. [PPh4][H2NMe2][(UO2)2(C7)3] (4) and [PPh3Me]2[(UO2)2(C8)3] (5) contain 1D chains, either ladderlike or containing doubly bridged dimers, while [PPh3Me]2[(UO2)2(C9)3]⋅2H2O (6) displays interdigitated, strongly corrugated honeycomb 2D nets. Ladderlike 1D polymers in [Cu(R,S-Me6cyclam)][(UO2)2(C7)2(C2O4)]⋅4H2O (7) are associated into columns 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) due to axial coordination of the nickel(II) centre, 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%.

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

“…68 We have discussed elsewhere 41 the possibility that energy transfer between close uranyl centres might prolong excited state lifetimes and thus that U⋅⋅⋅U separations within lattices may be important criteria in relation to PLQY values but the shortest U⋅⋅⋅U distance does not seem to be a relevant parameter in the case of complex 4 since, at 8.0460(3) Å (interchain), it is indeed larger than the values measured in the two most strongly emitting complexes cited above (5.511 and 5.232 Å, respectively), but comparable to distances in some much more weakly emitting species. 41 We have also considered that phosphonium cations may act as quenching centres and thus that U⋅⋅⋅P separations may be significant but the shortest U⋅⋅⋅P distance in 4, 6.750(3) Å, is within the range found in a series of complexes with smaller PLQYs, 41 which suggests that this is not the dominant factor here. This also appears to be the case for the non-emissive complex 5, where the shortest U⋅⋅⋅P separation [U1⋅⋅⋅P1 6.251(6) Å] is longer than that in emissive relatives.…”

“…synthesized as previously described. 25,41 Resolution of [Co(en)3] 3+ (en = ethylenediamine) by R,R-tartrate has been known for long, 42,43 and Λ-[Co(en)3](H2R,R-tart)Cl⋅2H2O, where H4R,Rtart is R,R-tartaric acid, was obtained as described. Elemental analyses were performed by MEDAC Ltd. at Chobham, UK.…”

“…This also appears to be the case for the non-emissive complex 5, where the shortest U⋅⋅⋅P separation [U1⋅⋅⋅P1 6.251(6) Å] is longer than that in emissive relatives. 41…”

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

“…16 In order to investigate more fully the structuredirecting role of counterions or coligands with this family of closely related phenylenedicarboxylates, and the possible differences related to the isomeric form chosen, we have now synthesized 14 synthesized as previously reported. 17,18 Elemental analyses were performed by MEDAC Ltd. at Chobham, UK. For all syntheses, the mixtures in demineralized water/organic solvent were placed in 10 mL tightly closed glass vessels and heated at 140 °C under autogenous pressure.…”

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

“…[Ni(cyclam)(NO3)2] and N(R,S,R,S)-[Cu(R,S-Me6cyclam)(NO3)2] were synthesized as previously reported. 13,14 The sample of H4CBTC used was previously shown to contain only the cis,trans,cis (ctc) isomer. 10 Elemental analyses were performed by MEDAC Ltd. at Chobham, UK.…”