Peculiarities of the Supramolecular Assembly of Tetraethylammonium and 3‑Bromopropionate Ions in Uranyl, Neptunyl, and Plutonyl Coordination Compounds

Synthesis and X-ray diffraction studies of {N­(C₂H₅)₄}­[AnO₂(C₂H₄BrCOO)₃] [An = U (I), Np (II), or Pu (III)] and C₂H₄BrCOOH (IV), where C₂H₄BrCOO^– is an anion of the 3-bromopropionic acid, are reported. The isostructural coordination compounds I–III contain mononuclear anionic complexes [AnO₂(C₂H₄BrCOO)₃]⁻ belonging to the crystal chemical group AB⁰¹₃ (A = AnO₂²⁺; B⁰¹ = C₂H₄BrCOO^–). In the crystal structure of IV, the C₂H₄BrCOOH molecules are hydrogen bonded into centrosymmetric dimers R₂²(8). Using the method of molecular Voronoi–Dirichlet (VD) polyhedra, the features of intermolecular interactions in crystals of I–IV are discussed in support of the results of IR and UV spectroscopy experiments. Actinide contraction in I–III manifests itself in a regular reduction of the average length of the axial and equatorial bonds in hexagonal bipyramids AnO₈, in an increase in ν_as(AnO₂²⁺) wavenumbers, and in a simultaneous decrease in the volume and sphericity degree of VD polyhedra of An atoms in the U–Np–Pu series. The title compounds represent an interesting architecture, where 3-bromopropionate ions penetrate through the square 4⁴ net of tetraethylammonium ions and thus bind adjacent nets via the “locking effect”.