Solvothermal Synthesis of Tetravalent Uranium with Isophthalate or Pyromellitate Ligands

Abstract

Three new coordination polymers bearing tetravalent uranium have been isolated with the O‐donor ligands such as isophthalate (1,3‐bdc) or pyromellitate (btec). The compounds 1 and 3 have been solvothermaly synthesized in N,N‐dimethylformamide (DMF). The crystal structure of U(1,3‐bdc)2(DMF) (1) is built up from discrete tricapped trigonal‐primastic UO9 units, for which one carbonyl oxygen atom from DMF is bound to uranium. The connection of the UO9 units with the isophthalate linkers occurs in a chelating and bidentate fashion and gives rise to the formation of a 3D framework, delimiting narrow channels running along the [101] direction. Upon heating, the DMF molecules are removed, generating the second phase U(1,3‐bdc)2 (2) compound, closely related to 1. Indeed, the coordination environment of uranium is reduced to eight with a distorted square‐antiprismatic geometry. This transition induces the relative shrinkage of the network (ΔV = 23 %). The structure of the compound U(btec)(DMF)2 (3) also exhibits a 3D framework composed of an isolated bicapped square‐antiprismatic UO10 unit, for which two carbonyl oxygen atoms from DMF are bonded to uranium. Pyromellitate ensures the connection of the UO10 units through the carboxylate arms in a chelating mode. This results in the formation of a network with diamond‐shaped channels, developed along the c axis and encapsulating the DMF molecules. In contrast to 1, no stable phase is observed upon removing the DMF species by heating.

Mononuclear to Polynuclear UIV Structural Units: Effects of Reaction Conditions on U‐Furoate Phase Formation

“…The reported compounds display a systematic increase in cluster size, from small tetrameric and hexameric oligomers to large clusters, while exhibiting similar ligand decoration and as such provide a catalog of U IV compounds that can be used to assess the influence of factors such as nuclearity on the U IV absorbance spectrum. Coordination environment, coordination number, and the solvent identity have similarly been shown to influence the observed transitions, thereby leading to changes in the peak position and relative intensity of the absorption bands; these factors were also taken into consideration and are discussed below.…”

“…To the best of our knowledge, the optical spectra of ligand bridged one‐dimensional U IV chains have not been reported previously. Shifts in the absorption bands in the optical spectra of closely related 3D frameworks built from mononuclear metal centers bridged by isophthalate or pyromellitate ligands have been observed and are attributed to changes in the coordination environment around the uranium metal centers, yet the degree of splitting observed for 1 is fairly unique for higher coordinate U IV complexes and extended networks.…”

Time-controlled synthesis of the 3D coordination polymer U(1,2,3-Hbtc)2 followed by the formation of molecular poly-oxo cluster {U14} containing hemimellitate uranium(iv)

“…1 53 or engaged in 3D frameworks for the desolvated uranium isophthalate (U(1,3-bdc) 2 ). 29 The unique crystallographically independent hemimellitate ligand acts as a tridentate linker with uranium; two of the carboxylate arms are linked to one uranium atom through a monodentate fashion whereas one carboxylate group is linked to two adjacent uranium centers in a bidentate bridging fashion (Fig. 1).…”

“…S6 †) exhibits a typical signature for the U(IV). The different 29,48 ). The X-ray thermodiffractogram of the washed compound 1 (Fig.…”

“…For instance, the use of the trimesate ligand resulted in the formation of channel-like structure with a honeycomb lattice based on a trinuclear U(IV)-centered building unit, 27 whereas the use of terephthalate, isophtalate, pyromellitate, mellitate linkers generated rather dense 3D frameworks with either tetranuclear, 18 dinuclear 28 or discrete units. 29 With the phthalate molecule, a layered structure has been obtained with ribbons involving U-O-U linkage connected to each other via the organic ditopic ligand. 28 Moreover, it was also demonstrated that the use of monotopic ligands, such as formate, triate, glycine or benzoate, favors the formation of discrete molecular poly-oxo clusters 30 with a wide range of nuclearities from a classical motif containing six U(IV) centers [31][32][33][34][35] up to a giant unit containing thirty eight U(IV) centers.…”