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Download fileTetrahydrofurantetracarboxylic Acid: An Isomerizable Framework-Forming Ligand in Homo- and Heterometallic Complexes with UO22+, Ag+, and Pb2+
journal contribution
posted on 2016-10-13, 00:00 authored by Pierre Thuéry, Jack Harrowfield(2R*,3R*,4S*,5S*)-Tetrahydrofurantetracarboxylic acid (H4thftc) has been
used as a ligand to synthesize five uranyl
ion complexes, three of them including additional silver(I) or lead(II)
metal cations. The complex [C(NH2)3]2[UO2(H2thftc)2] (1),
obtained in water at room temperature, is a discrete mononuclear species
in which the uranyl cation is bound to the tridentate coordination
site (involving the ether oxygen atom and the two adjoining carboxylate
groups) of two ligands, and extensive hydrogen bonding is present.
All the other complexes were obtained under (solvo)-hydrothermal conditions
giving rise to higher degrees of ligand deprotonation. [(UO2)3(Hthftc)2(H2O)2]·2CH3CN (2) crystallizes as a two-dimensional (2D)
network with the V2O5 topological type, whereas
in the heterometallic complex [(UO2)3Ag2(thftc)2(H2O)2]·2H2O (3), similar 2D layers are assembled into a
three-dimensional (3D) framework by bridging Ag2 moieties.
Lead(II) replaces uranyl in the tridentate coordination site in the
two complexes [UO2Pb(thftc)(H2O)] (4) and [UO2Pb(thftc)(H2O)2]·H2O (5), and the high connectivity of the ligand,
bound to seven metal cations through diverse chelating and bridging
interactions, ensures that both are 3D frameworks. Bonding of a uranyl
oxo group to either silver(I) or lead(II) is apparent in complexes 3 and 5. The homometallic complexes [Ag3(Hthftc)] (6) and [Pb2(thftc)(H2O)] (7), devoid of uranyl cations, are both 3D frameworks
in which the ligand is bound to 11 or 9 metal cations, respectively.
Complex 6 is the single instance in this series in which
the ligand, originally in the trans,cis,trans form,
has undergone isomerization into the chiral cis,trans,trans (2R*,3S*,4S*,5S*) form through a process probably involving an ene-diol
intermediate. Only complexes 1, 2, and 4 display intense and well-resolved emission bands under excitation
at 420 nm in the solid state, the uranyl emission of complexes 3 and 5 being largely quenched.