Synthesis, Structures, and Properties of Uranyl Hybrids Constructed by a Variety of Mono- and Polycarboxylic Acids

A series of uranyl–organic coordination polymers have been hydrothermally synthesized by using a variety of carboxylic ligands, 3,3′-((2-((3-carboxyphenoxy)­methyl)-2-methylpropane-1,3-diyl)­bis­(oxy))­dibenzoic acid (H<sub>3</sub>L<sup>1</sup>), 4,4′-(3-(4-carboxyphenethyl)-3-hydroxypentane-1,5-diyl)­dibenzoic acid (H<sub>3</sub>L<sup>2</sup>), chelidamic acid (H<sub>2</sub>L<sup>3</sup>), and benzoic acid (HL<sup>4</sup>) in the presence of N-bearing coligands, including 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), 1-([1,1′-biphenyl]-4-yl)-1<i>H</i>-imidazole (bpi), and 1,4-di­(1<i>H</i>-imidazol-1-yl)­benzene (dib). Compounds (UO<sub>2</sub>)­(HL<sup>1</sup>) (<b>1</b>) and Zn­(H<sub>2</sub>O)<sub>3</sub>(UO<sub>2</sub>)<sub>2</sub>(O)­(OH)­(L<sup>2</sup>)·H<sub>2</sub>O (<b>2</b>) are constructed by semirigid ligands. The former is a one-dimensional ribbon-like structure with UO<sub>7</sub> pentagonal bipyramids as the building unit, while the latter adopts a tetramer of UO<sub>7</sub> pentagonal bipyramids to build a layered structure. Mononuclear UO<sub>7</sub> pentagonal bipyramids are connected by L<sup>3</sup> groups to generate a two-dimensional arrangement of UO<sub>2</sub>(L<sup>3</sup>)­(H<sub>2</sub>dib)<sub>0.5</sub> (<b>3</b>), in which the protonated dib molecules provide space filling and form π···π interactions with the layers. Compounds UO<sub>2</sub>(L<sup>3</sup>)­(phen) (<b>4</b>), UO<sub>2</sub>(L<sup>3</sup>)<sub>2</sub>(Hbpi)<sub>2</sub> (<b>5</b>), and UO<sub>2</sub>(L<sup>4</sup>)<sub>2</sub>(bipy) (<b>6</b>) are molecular complexes, in which <b>4</b> and <b>6</b> are neutral, and <b>5</b> comprises protonated bpi as the counterion. The uranyl center in compound <b>4</b> is chelated by one phen and one L<sup>3</sup> group to form a UO<sub>5</sub>N<sub>2</sub> pentagonal bipyramid, while in compound <b>5</b>, two L<sup>3</sup> groups are coordinated to an uranyl center, producing a UO<sub>8</sub> polyhedron. Compound <b>6</b> consists of a UO<sub>6</sub>N<sub>2</sub> polyhedron of uranyl unit coordinated by one bipy and two benzoate groups. Compounds Zn­(phen)<sub>3</sub>[(UO<sub>2</sub>)­(C<sub>2</sub>O<sub>4</sub>)­(L<sup>4</sup>)]<sub>2</sub> (<b>7</b>) and Zn­(bpi)<sub>2</sub>(UO<sub>2</sub>)­(O)­(C<sub>2</sub>O<sub>4</sub>)<sub>0.5</sub>(L<sup>4</sup>)·H<sub>2</sub>O (<b>8</b>) feature one-dimensional structures. In <b>7</b>, UO<sub>7</sub> pentagonal bipyramids are alternatively connected by oxalate groups to form the chain, in which unidentate benzoate groups are coordinated to the uranium atoms. Zn­(phen)<sub>3</sub> cations fill the void space of the chains to compensate the negative charge. Differently, the chain of <b>8</b> can be seen as the heterometallic tetramer of UO<sub>7</sub> and ZnO<sub>2</sub>N<sub>2</sub> polyhedra connected by oxalate groups, and then bpi and benzoate groups are coordinated to the chain. All of the compounds have been characterized by IR and photoluminescent spectroscopy, and compounds <b>2</b>, <b>3</b>,<b> 5</b>,<b> 6</b>, and <b>8</b> exhibit characteristic emissions of uranyl cations.