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

Abstract

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,Nʹdimethylpropyleneurea (DMPU) in the uranyl coordination sphere produces the four complexes [UO2(1,2pda)(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 daisychain-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 phosphoniumcontaining complexes [PPh3Me]2[(UO2)2(1,3-pda)3] (13) and [PPh4]2[(UO2)2(1,4-pda)3] (14) contain ladder-like and daisychain-like monoperiodic polymers, respectively, while only the latter geometry is found in the mixedcation complexes [PPh3Me][H2NMe2][(UO2)2(1,4-pda)3]H2O (15) and [PPh3Me][H2NMe2][(UO2)2(1,2-pda)(1,4pda)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.

Stepwise Introduction of Flexibility into Aromatic Dicarboxylates Forming Uranyl Ion Coordination Polymers: a Comparison of 2‐Carboxyphenylacetate and 1,2‐Phenylenediacetate

“…Uranium atoms are 4-c nodes, cpa 2are 3-c nodes and nickel atoms are simple links, and the network has the vertex symbol {4.6 2 } 2 {4 2 .6 2 .8 2 } and the topological type 3,4L13, previously found in some transition metal ion complexes, [26,27] and also in some uranyl compounds, [9,28,29] with one particular example involving 1,4-pda 2-. [13] No significant π-stacking interaction is apparent in this case, the only weak interactions worthy of note being the hydrogen bonds between the amine groups of R,S [13] The centrosymmetric, diprotonated dmaepH 2 2 + cation, where the piperazine ring has a chair CN (6) where the coordination polymer is triperiodic, the first found to be formed with the 1,2-pda 2À ligand (Figure 6). The two independent uranyl cations are tris-chelated by carboxylates from three separate ligands, two of one chirality and one of the other [UÀ O(oxo), 1.773(3)-1.776(3) Å; UÀ O(carboxylato), 2.414(3)-2.510(3) Å], the ligand role and pseudo-C 2 conformation being as in 5.…”

“…[10] The uranyl cation is bound to three cpa 2- [110], and it contains centrosymmetric, dimeric units of edge-sharing ura-nium coordination polyhedra. While unsolvated forms of the neutral complexes containing phthalate (pht 2À ) or 1,2-pda 2-have not been structurally characterized, at least in the complex [UO 2 (1,2-pda)]•CH 3 CN, [13] unlike [UO 2 (pht)(H 2 O)]•H 2 O, [17] the solvent molecule is not coordinated. The 1,2-pda 2complex is a diperiodic polymer in which the ligand acts as a bis(k 2 O,O') bridging unit only and although the pht 2complex is a monoperiodic (but double stranded) polymer, the carboxylate groups are involved in seven-membered chelate ring formation along with μ 2 -k 1 O:k 1 O' bridging.…”

“…In neither case is there formation of a four-membered k 2 O,O' chelate ring, even though such rings are seen in other uranyl ion complexes of both ligands. [10][11][12][13]18] The chains in 1 are arranged in layers parallel to (001), which are interdigitated and tightly packed, with a Kitaigorodski packing index (KPI, calculated with PLATON [19] ) of 0.74. Analysis of short contacts with PLATON indicates that interlayer parallel-displaced π-stacking interactions may be present [centroid•••centroid distance, 3.8326(14) Å; dihedral angle, 0°; slippage, 1.31 Å].…”

“…Polycarboxylates are ligands among the most used for the synthesis of uranyl ion-containing coordination polymers and frameworks, [1][2][3][4][5] and, considering the huge range of geometries and denticities covered by these anions, this allows for detailed studies of the effect of fine modifications of the ligands upon the structure of the complexes formed. In particular, comparison of the structures of uranyl ion complexes of homologous pairs of ligands such as adamantane-dicarboxylate and -diacetate, [6][7][8][9] or phthalate [10] and 1,2-phenylenediacetate [11][12][13] has enabled some assessment of the influence of rotation about additional CÀ C single bonds to be made. In these particular cases, however, the influence is that of the addition of two such bonds and comparisons involving the singly modified ligands 3carboxylato-adamantane-1-acetate or 2-carboxyphenylacetate are lacking.…”

Uranyl Ion Complexes of Polycarboxylates: Steps towards Isolated Photoactive Cavities

“…As solvothermal synthesis [113,114] is widely applied for the isolation of crystalline uranyl ion complexes, another need is for more data concerning kinetics and equilibria of complex formation under conditions of high temperature and pressure, particularly in mixed solvents. Finally, it is essential to note that the crystal structures of known uranyl ion complexes are frequently seen [115][116][117][118] to be sensitive to a wide range of weak interactions, so that the supramolecular behaviour of a bound ligand is a crucial aspect of its design but one yet to be mastered.…”