Complexes of Np(VI) with Cyclobutanecarboxylic Acid Anions and Single-Charged Cations in the Outer Sphere: [NH4][NpO2(cbc)3], [C(NH2)3][NpO2(cbc)3], and [N(CH3)4][NpO2(cbc)3]

Abstract

Three new Np(VI) complexes with cyclobutanecarboxylic acid anions and single-charged outer-sphere anions: ammonium, [NH₄][NpO₂(cbc)₃] (I), guanidinium, [C(NH₂)₃][NpO₂(cbc)₃] (II), and tetramethyl-ammonium, [N(CH₃)₄][NpO₂(cbc)₃] (III), were synthesized and studied by single-crystal X-ray diffraction. The coordination surrounding of the Np atoms in I–III is a hexagonal bipyramid with three bidentate cyclic C₄H₇COO⁻ anions in the equatorial belt. In compounds I and II, the outer-sphere \(\rm{NH}_4^+\) and \(\rm{C}(NH_2)_3^+\) cations are linked with the anionic complexes [NpO₂(cbc)₃]⁻ to form a three-dimensional framework via N–H⋯O hydrogen bonding. In complex III, large outer-sphere \(\rm{N}(CH_3)_4^+\) cations cause differences in the structure of the anionic complexes [NpO₂(cbc)₃]⁻.