Coordination polymers of uranium(iv) terephthalates

Abstract

A series of tetravalent uranium terephthalates has been solvothermally synthesized in the solvent N,N-dimethylformamide (DMF) at temperature 100-150 °C with different water amounts. Composition diagrams have been determined for the U(4+) metallic cation in the presence of terephthalic acid, and their crystal structures revealed the occurrence of two- or three-dimensional coordination polymers. In the absence of water, a mixture of two polytypes T-U(2)Cl(2)(bdc)(3)(DMF)(4) (1) and M-U(2)Cl(2)(bdc)(3)(DMF)(4) (2) has been identified at low temperature (100-110 °C) for bdc/U = 1-4 (bdc = terephthalate linker). Their structures are built up from isolated uranium centers in nine-fold coordination, surrounded by 6 carboxyl oxygen atoms, 2 oxygen atoms coming from DMF molecules and one chlorine atom. The uranium cations are linked to each other through the bdc ligand in order to generate a 3D framework. By increasing the temperature (130-150 °C), a layered like compound has been isolated, U(2)(bdc)(4)(DMF)(4) (3). It is composed of discrete actinide centers in ten-fold coordination, with 8 carboxyl oxygen atoms and 2 oxygen atoms from DMF molecules. The connection of the UO10 units with the bdc linkers generates 2D sheets. When a controlled amount of water is added to the reaction medium, the crystallization of the UiO-66-like U(6)O(4)(OH)(4)(H(2)O)(6)(bdc)(6)·10DMF solid (containing a hexanuclear sub-unit) is observed for temperature 110-120 °C and the H(2)O/U molar ratio in the range of 2-10. At higher temperature (140-150 °C), a distinct phase appeared, U(2)O(2)(bdc)(2)(DMF) (4), which consists of infinite chains of uranium centers, linked to each other via the bdc ligands. Higher water contents led to the formation of urania UO(2).

Solvothermal Synthesis of Tetravalent Uranium with Isophthalate or Pyromellitate Ligands

“…In previous works, especially in the case of uranium terephthalates [27] and benzoate, [23] the role of water has been underlined since it favors hydrolysis and condensation of the uranium centers, which gives rise to the formation of inorganic polynuclear motifs. As expected, the anhydrous mixture used for the preparation of the phase U(1,3-bdc) 2 -(DMF) (1) generates a framework including only isolated uranium monomers.…”

“…If we compare the other systems where the role of water was clearly identified in the formation of the final structure [23,26,27] and the reaction medium involving pyromellitic acid, the main difference lies in the acidity strength of the selected carboxylic acid. Indeed, while the pK a values of pyromellitic acid are ranging from 1.92 to 5.63, those of benzoic, isophthalic or terephthalic acid do not exceed 4.82.…”

“…[4] During the last decades, several investigations have been devoted to the crystallization of new tetravalent uranium carboxylates. These led to the production of approximately twenty new structures that were isolated by using various organic ligands (formate, [13] acetate, [14][15][16] glycolate, [17] dipicolinate, [18][19][20] malonate, [21] fumarate, [22] benzoate, [23][24][25] terephthalate, [26,27] 4,4Ј-biphenyldicarboxylate, [26] 2,6-naphthalenedicarboxylate, [26] trimesate [28] ). The structural diversity of tetravalent uranium chemistry was also highlighted by the isolation of different nuclearities of inorganic building units, such as monomers, trimers, [28,[17][18][19][20][21] tetramers, [14][15][16]22] hexamers, [13,22,25,26] decamers, [24] hexadecamers, [24] chains [29] or, more recently, the U 38 poly-oxo cluster.…”

Coordination of Tetravalent Actinides (An=ThIV, UIV, NpIV, PuIV) with DOTA: From Dimers to Hexamers

“…[18] Another clusterw ith 12 uranium cations,[ U 12 (OH) 8 O 12 ], synthesized in presenceo ft riflate and iodate, was isolated. [19] Overall, the most represented families of the oxo-hydroxoc lusters are the hexanuclear species, [An 6 (OH) 4 O 4 ] 12 + ,s tabilized by small organic ligandss uch as triflate, [19] phosphate, [20] sulfate, [21] isocyanurate, [22] carboxylic acids, [23][24][25][26][27][28] or small amino acids. [29,30] Uncommon structures with a[ An 6 (O) 4 (OH) 4 ] 12 + core, stabilized by aromaticl igands connected to the actinide through p-p interactions, werea lso described.…”

Uranium(VI) hybrid materials with [(UO2)3(µ3‐O)(µ2‐OH)3]+as the sub–building unit via uranyl–cation interactions

“…[12] 1,4-benzenedicarboxylic acid (H 2 bdc) is a very common aromatic dicarboxylate ligand widely used as a good linker to build various frameworks with transition metals and lanthanide ions. [13] As for its compounds with early actinide ions, several structures with tetravalent ions, e. g. Th(IV) [14] and U(IV), [15] have been reported. In addition, a few uranyl complexes with both 1D and 2D structures [16] and only three mixed ligand complexes with 3D structures [17] have been reported.…”