Syntheses and Structures of a Series of Uranyl Phosphonates and Sulfonates: An Insight into Their Correlations and Discrepancies

Six uranyl phosphonates and sulfonates
have been hydrothermally synthesized, namely, (H2tib)­[(UO2)3(PO3C6H5)4]·2H2O (UPhP-1), Zn­(pi)2(UO2)­(PO3C6H5)2 (UPhP-2), Zn­(dib)­(UO2)­(PO3C6H5)2·2H2O (UPhP-3), (HTEA)­[(UO2)­(5-SP)] (USP-1), (Hdib)2[(UO2)2(OH)­(O)­(5-SP)] (USP-2), and Zn­(phen)3(UO2)2(3-SP)2 (USP-3) (tib = 1,3,5-tri­(1H-imidazol-1-yl)­benzene,
pi = 1-phenyl-1H-imidazole, dib = 1,4-di­(1H-imidazol-1-yl)­benzene,
TEA = triethylamine, phen = 1,10-phenanthroline, 5-SP = 5-sulfoisophthalic
acid, and 3-SP = 3-sulfoisophthalic acid). UPhP-1 has
been determined to be a layered structure constructed by UO7 pentagonal bipyramids, UO6 octahedra, and phenylphosphonates.
Protonated tib plays a role in balancing the negative charge and holding
its structure together. UPhP-2 is made up of UO6 octahedra, ZnO2N2 tetrahedra and PO3C tetrahedra in phenylphosphonates, forming a 1D assembly, which
is stabilized by chelate phen ligand. Further connection of such chainlike
structure via dib yields a 2D layered architecture of UPhP-3. Although sulfonate group possesses similar tetrahedral structure
as the phosphonate group, a unidentated coordination mode is only
found in this work. UO7 pentagonal bipyramids are linked
by 5-SP to form the layered assembly of USP-1. USP-2 also consists of the same sulfonate ligand, but features
tetranulear uranyl clusters. Similarly, protonated TEA and dib molecules
enable stabilization of their structures, respectively. Formed by
dinuclear uranyl cluster and 3-SP ligand, USP-3 appears
as a 1D arrangement, in which Zn­(phen)3 acts as the counterion
to compensate the negative charge. All of these compounds have been
characterized by IR and photoluminescent spectroscopy. Their characteristic
emissions have been attributed as transition properties of uranyl
cations.