Syntheses, Crystal Structures, and Nonlinear Optical Activity of Cs2Ba[AnO2(C2H5COO)3]4 (An = U, Np, Pu) and Unprecedented Octanuclear Complex Units in KR2(H2O)8[UO2(C2H5COO)3]5 (R = Sr, Ba)

• Published in: Inorganic chemistry 2017-06, Vol.56 (12), p.7151-7160
• Main Authors: Serezhkin, Viktor N, Grigoriev, Mikhail S, Abdulmyanov, Aleksey R, Fedoseev, Aleksandr M, Savchenkov, Anton V, Stefanovich, Sergey Yu, Serezhkina, Larisa B
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.7b00809

X-ray diffraction was applied to the elucidation of crystal structures of single crystals of Cs2Ba­[AnO2(C2H5COO)3]4, where An = U­(I), Np­(II), Pu­(III), and KR2(H2O)8[UO2(C2H5COO)3]5, where R = Sr­(IV), Ba (polymorphs V-a and V - b). FTIR spectra were analyzed for the uranium-containing crystals I, I V, and V - b. Isostructural cubic crystals I–I I I are constructed of typical mononuclear anionic complex units [AnO2(C2H5COO)3]− and charge-balancing Cs and Ba cations. Features of actinide contraction in the six U–Np–Pu isostructural series known to date are analyzed. In crystal structures of IV and V two typical complexes [UO2(C2H5COO)3]− bind with a hydrated Sr or Ba cation to form the rare trinuclear neutral complex unit {R(H2O)4[UO2(C2H5COO)3]2}, where R = Sr, Ba. Two such trinuclear units and one typical mononuclear unit further bind with a K cation to form the unprecedented octanuclear neutral complex unit K­[UO2(C2H5COO)3]­{R­(H2O)4[UO2(C2H5COO)3]2}2. As the derived polynuclear complexes of uranyl ion with carboxylate ligands in the crystal structures of IV and V are not the first but are rare examples, the equilibrium between mono and polynuclear complex units in aqueous solutions is discussed. The two polymorphic modifications V-a and V-b were studied at 100 K and at room temperature, respectively. Peculiarities of noncovalent interactions in crystal structures of the two polymorphs are revealed using Voronoi–Dirichlet tessellation. The nonlinear optical activity of noncentrosymmetric crystals I was estimated by its ability for second harmonic generation.