One- to three-dimensional uranyl–organic assemblies with 3-sulfophthalic and 5-sulfoisophthalic acids

Abstract

Complexes formed by uranyl ions with sulfonate derivatives of phthalic and isophthalic acids under hydrothermal conditions have been investigated. The reaction of uranyl nitrate with 3-sulfophthalic acid (3-SPH₃) in the presence of 2,2′-bipyridine (2,2′-bipy) gave the complex [2,2′-bipyH][UO₂(3-SP)] (1), which is a one-dimensional coordination polymer in which the three functional groups of 3-SP³⁻ are coordinated. Four complexes were obtained from uranyl nitrate and the lithium salt of 5-sulfoisophthalic acid (5-SIPH₂Li). In the presence of additional nickel(II) ions and bipyrimidine (bipym), the complex [Ni₂(bipym)₃(H₂O)₄][UO₂(5-SIP)(NO₃)]₂·6H₂O (2) is formed, in which uranyl-containing one-dimensional chains result from bridging by 5-SIP³⁻ through its carboxylate groups only. The two compounds obtained in the presence of triethylamine and pyrazine (pyz), [HNEt₃][UO₂(5-SIP)] (3) and [Hpyz][UO₂(5-SIP)]·2.5H₂O (4), display both carboxylate and sulfonate coordination, resulting in the formation of two-dimensional assemblies with {4⁴·6²} topology. The use of 1,4-diazabicyclo[2.2.2]octane (DABCO) as a base gives the complex [H₂DABCO][UO₂(5-SIP)(H₂O)]₂·4H₂O (5) which crystallizes as a three-dimensional framework with channels containing the counter-ions. The structure of 5 comprises uranyl–organic layers, in which the 5-SIP³⁻ ligands are stacked in rows held by π-stacking interactions; these layers are connected to one another by uranyl groups orthogonal to those in the layers. The variation of dimensionality in complexes 3–5, which likely arises from structure-directing effects exerted by the counter-ions, is discussed in relation with geometry differences around the ligand coordination sites.