Uranium(vi) complexes with isonicotinic acid: from monomer to 2D polymer with unique U–N bonding

Abstract

Two new uranium(VI) complexes with isonicotinic acid (HINT) have been synthesized and characterized. [(UO₂)(NO₃)₂(HINT)₂] (1) has a monomeric structure constructed of a hexagonal bipyramidal uranyl centre, two nitrate anions and two monodentate HINT in trans-positions. [(UO₂)(OH)(INT)] (2) has a two-dimensional (2D) polymeric structure constructed of uranyl hydroxyl 1D pillars and μ₃-bridging INT anions; the first observation of INT in μ₃-bridging mode for U(VI) ion via U–N bonding. Thermal analysis confirmed both complexes lost coordinated INT ligands followed by further decomposition to form U₃O₈. Raman spectroscopy has confirmed the presence of uranyl ion and INT ligand in both complexes as well as the existence of nitrate vibrations in 1 and hydroxyl vibrations in 2. Their photoluminescence properties have been investigated.