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-pdaH(2)) 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)]center dot 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)]center dot H2O (7) and [H2NMe2](2)[(UO2)(2)(1,2-pda)(3)]center dot 3H(2)O (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)]center dot 0.5H(2)O (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)]center dot 0.5H(2)O center dot 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)]center dot 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.