Rare Three-Dimensional Uranyl-Biphenyl-3,3'-disulfonyl-4,4'-dicarboxylate Frameworks: Crystal Structures, Proton Conductivity, and Luminescence.

ABSTRACT

Due to the intrinsic coordination preference of the linear uranyl unit, uranyl-organic frameworks (UOFs) are generally prone to exhibiting low-dimensional structures. Reactions of uranyl nitrate with biphenyl-3,3'-disulfonyl-4,4'-dicarboxylic acid dipotassium salt (K2H2BPDSDC) under different conditions led to three UOFs, namely, {(Me2NH2)[K2(UO2)3(µ3-O)(µ3-OH)2(µ2-OH)(BPDSDC)(H2O)3]·4DMF}n (1), {[K2(UO2)(µ3-O)(BPDSDC)0.5(H2O)2]}n (2), and {(Me2NH2)2.5[K1.5(UO2)(BPDSDC)1.5(H2O)3]}n (3). Compounds 1 and 2 contain one-dimensional (1D) ribbon structures formed from UO22+ units bridged by µ3-O atoms and carboxylate groups. The 1D ribbons in 1 are linked by K+ atoms to form a two-dimensional (2D) layer, which is further pillared by the biphenyl units to give a three-dimensional (3D) framework. For 2, the oxygen atoms of UO22+ units in each 1D ribbon bridge the K+ atoms to form four -[K-O-K]n- infinite chains located above and below the ribbon. The 1D ribbons in 2 are bridged by sulfonate groups to generate a 3D substructure featuring 1D channels occupied by biphenyl moieties. In 3, each mononuclear [(UO2)(COO)3] unit is bridged by three K+ atoms to form a 3D substructure featuring 1D small left-handed and large righted helical channels occluded by biphenyl moieties. Compound 2 exhibits an excellent proton conductivity with the highest conductivity of 1.07 × 10-3 S cm-1. The inner walls of 1D channels of 2 are full of the hydrophilic sulfonate groups, which boost enrichment of the guest water molecules, thus resulting in a high proton conductivity. Finally, temperature dependence of fluorescent studies showed that compounds 1 and 2 display the characteristic uranyl emissions. This work presents the elegant examples of the rarely explored 3D UOFs and expands the potentials of UOFs.