Variable Dimensionality in the UO2(CH3CO2)2·2H2O/HF/Isonicotinic Acid System: Synthesis and Structures of Zero-, One-, and Two-Dimensional Uranium Isonicotinates

Abstract

Four new uranium isonicotinate framework solids were synthesized in the UO2(CH3CO2)·2H2O/HF/isonicotinic acid system under hydrothermal conditions. The isolated uranium isonicotinates span a range of dimensionalities from zero-dimensional UO2(C5H5NCO2)(CH3CO2)2 (1), one-dimensional [UO2F2][C5H5NCO2] (2) and [UO2F3][C5H6NCO2]·0.5H2O (3), and two-dimensional [UO2F2]2[C5H5NCO2]·H2O (4). Regions of phase stability were determined using composition space diagrams, which were used to demonstrate the dependence of product composition on the initial reagent concentrations. The molecular zero-dimensional UO2(C5H5NCO2)(CH3CO2)2 (1) consists of UO8 hexagonal bipyramids in which the [UO2]2+ center is coordinated by two acetate and one isonicotinate ligands. The first one-dimensional compound, [UO2F2][C5H5NCO2] (2), contains a chain of edge-sharing [UO3F4] pentagonal bipyramids with isonicotinate ligands separating the chains. The second one-dimensional compound, [UO2F3][C5H6NCO2]·0.5H2O (3), is constructed from edge-sharing chains of [UO2F5] pentagonal bipyramids and a hydrogen-bonding network of isonicotinic acid. [UO2F2]2[C5H5NCO2]·H2O (4) contains uranium oxyfluoride layers consisting of edge-sharing dimers of UO3F4 and the corner-sharing UO3F4 chains, where the UO3F4 dimer is corner-linked with UO3F4 chains.