Synthesis and physical property of uranium-containing porous coordination polymer

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The colors of the multi-valent complexes of uranium, neptunium and plutonium strongly depend on the oxidation state of the metal ion, and it is often possible to determine the oxidation state of the metal ion from the color of its solutions. Given the fact that uranium is only weakly radioactive due to the long half-lives of its naturally occurring isotopes, uranium-containing compounds could find some applications as advanced materials.In the present study, temperature-dependent yellow-to-red colour changes of uranyl thiocyanate complexes with 1-alkyl-3-methylimidazolium cations have been studied by different spectroscopic methods and this phenomenon is attributed to changes in the local environment of the uranyl ion, including the coordination number, as well as to cation. anion interactions.The structure contained disorder in three of the NCS^-anions and one C_2mim^+cation. The U-O bond distances(1.766(8), 1.765(9) A) and the O-U-O bond angle(171.2(9) 1°) are in the range expected for the uranyl moiety. The mean U-N distance is 2.45 A which is close to that seen in[DPSH]_3[UO_2(SCN)_5](DPSH=2-pyridylthio-2-pyridinium) and Cs_3[UO_2(SCN)_5] which both have mean U-N distances of 2.45 A. However, in this structure there are large variations from the mean with much shorter distances(U-N=2.398(11) A) and large distances(U-N=2.513(10) A), Time-resolved luminescence spectra, at 77 K, of neat uranyl which have not been known for uranyl-thiocyanates. The anisotropic structure could play an important role in the chromic reactions. Due to the weak interaction between the thiocyanate and imidazolium cation, labile and flexible coordination geometries for thiocyanate are allowed.