Crystal growth, structural characterization, cation–cation interaction classification, and optical properties of uranium(vi) containing oxychlorides, A4U5O16Cl2 (A = K, Rb), Cs5U7O22Cl3, and AUO3Cl (A = Rb, Cs)

Abstract

Single crystals of five new alkali metal uranium oxychlorides, K₄U₅O₁₆Cl₂, Rb₄U₅O₁₆Cl₂, Cs₅U₇O₂₂Cl₃, RbUO₃Cl, and CsUO₃Cl, have been grown from molten chloride fluxes and structurally characterized by single crystal X-ray diffraction. All of the materials are monoclinic. The first three crystallize in the space group P2₁/n and exhibit a 2D layered structure with a novel layer topology, consisting of UO₆, UO₇, and UO₄Cl₂ polyhedra and cation–cation interactions (CCIs) within the plane of the uranyl sheet. A general cation–cation classification scheme is presented. RbUO₃Cl and CsUO₃Cl crystallize in the space group P2₁/m and exhibit 1D zipper-like chains of UO₅Cl₂ polyhedra. The lattice parameters of the new oxychlorides are: K₄U₅O₁₆Cl₂, a = 9.9574(4) Å, b = 6.9766(3) Å, c = 14.3920(6) Å, and β = 105.7690(10)°; Rb₄U₅O₁₆Cl₂, a = 10.2164(4) Å, b = 7.0160(3) Å, c = 14.4930(5) Å, and β = 103.8290(10)°; Cs₅U₇O₂₂Cl₃, a = 10.6214(5) Å, b = 18.1071(8) Å, c = 16.0857(7) Å, and β = 102.9850(10)°; RbUO₃Cl, a = 7.3602(6) Å, b = 4.1127(3) Å, c = 8.5556(7) Å, and β = 104.602(2)°; CsUO₃Cl, a = 7.7768(4) Å, b = 4.1245(2) Å, c = 8.7701(5) Å, and β = 105.4680(10)°. The materials were further characterized by UV-vis reflectance spectroscopy and fluorescence spectroscopy.