Two uranyl–organic frameworks with pyridinecarboxylate ligands. A novel heterometallic uranyl–copper(II) complex with a cation–cation interaction

Reaction of uranyl nitrate with pyridine-2-carboxylic acid (HL1) under hydrothermal conditions gives the complex [(UO2)3(L1)4(NO3)2], 1, which differs from the previously reported molecular complex, obtained at room temperature, by the absence of water, coordinated and free, and the extended carboxylate bridging. Although the trimetallic basic unit is similar in both cases, 1 crystallizes as a two-dimensional assembly. A heterometallic complex results from the reaction of uranyl nitrate and copper(II) trifluoromethanesulfonate with nicotinic acid (pyridine-3-carboxylic acid, HL2), [UO2Cu(L2)2(NO3)2], 2, in which copper nicotinate two-dimensional subunits are bridged by uranyl nitrate groups to give a three-dimensional framework. The copper atom environment geometry is elongated octahedral, with one of the axial donors being a uranyl oxo group (cation–cation interaction).