Syntheses, structures and fluorescent properties of two novel coordination polymers in the U-Cu-H3pdc system

Two novel coordination polymers, UO2(C5H2N2O4) (H2O) (1) and (UO2) Cu(C5H2N2O4)(2)(H2O)(2) (2), have been prepared by the hydrothermal reaction of uranyl nitrate hexahydrate [(UO2(NO3)(2) center dot 6H(2)O], 3, 5-pyrazoledicarboxylic acid (H(3)pdc) and copper(II) nitrate hemipentahydrate (Cu(NO3)(2) center dot 2.5H(2)O) and characterized by single-crystal X-ray diffraction, thermogravimetric analyses (TGA) and fluorescence spectroscopy. Compound 1 (monoclinic, P2(1)/ c, a = 6.9556( 6) angstrom, b = 11.302( 1) angstrom, c = 10.5288( 9) angstrom, beta = 90.057(2)degrees and Z = 4) consists of a two-dimensional sheet containing uranyl hexagonal bipyramids. Compound 2 (triclinic, P-1, a = 5.1014( 7) angstrom, b = 7.6067(11) angstrom, c = 10.2910(15) angstrom, a = 72.380( 3)degrees, beta = 86.796( 3)degrees, gamma = 84.447( 3)degrees and Z = 1) consists of two-dimensional sheets. Both structures contain the linear UO22+ moiety and have extended networks built up from the H(3)pdc ligand. Compound 1 exhibits the characteristic UO22+ emission spectra when it is excited at the ligand or uranium excitation wavelength. With the addition of the copper metal center in compound 2, the uranium emission is absent regardless of the excitation wavelength.