One-dimensional uranium(VI) coordination polymers with pyridinecarboxylate ligands

Abstract

A method to produce picolinate ligand in situ under hydrothermal conditions has been used to synthesize four uranyl hydroxyl, oxo- and oxohydroxyl picolinato complexes. (UO2)(OH)(Pic) (1) (HPic=picolinic acid) contains 7-fold coordinated uranyl hydroxyl dimers linked through μ2-bridging Pic ligands forming a one-dimensional (1D) polymer. (NH4)[(UO2)3(O)2(OH)(Pic)2] (2) consists of 7-fold coordinated uranyl oxohydroxyl trinuclear units linked through both μ2- and μ3-Pic ligands forming a 1D polymer. (NH4)[(UO2)2(O)2(Pic)] (3) is constructed with 7-fold coordinated uranyl oxo-dinuclear units linked through oxo- and μ3-Pic ligands forming a 1D polymer. (NH4)[(UO2)4(O)2(OH)2(Pic)2(INT)]·H2O (4) (HINT=isonicotinic acid) is made of 7-fold coordinated uranyl oxohydroxyl tetranuclear units linked through both Pic and INT ligands forming a 1D polymer. All four polymers are thermal robust to 350°C. Raman spectroscopy confirmed the presence of uranyl ion and Pic ligand. In addition, red enhanced fluorescence emissions have been observed for both 1 and 4. The synthesis method, with the advantage of controlling uranyl hydrolysis and generating ligand in situ, provides a more reliable way to make new coordination polymers of carboxylate ligands with various uranyl hydrolysis species.