Crystal growth of novel 3D skeleton uranyl germanium complexes: influence of synthetic conditions on crystal structures.

Five centrosymmetric uranyl germanate compounds, KBrF(UO)(GeO), Rb(UO)(GeO)·0.5HO, Cs(UO)GeO and A(UO)(GeO) (A = Rb, Cs), were synthesized in this work. KBrF(UO)(GeO) and Rb(UO)(GeO)·0.5HO were obtained under mixed KF-KBr flux and hydrothermal conditions, respectively. Both structures crystallized in the triclinic P1[combining macron] space group and have similar anionic frameworks featuring novel hexagon shaped 12-membered channels. The condensation of two different types of SBU [UGe] pentamers (A) and (A2) results in the formation of KBrF(UO)(GeO) and Rb(UO)(GeO)·0.5HO frameworks. Cs(UO)GeO was obtained from a CsF-CsCl high temperature flux, and it also crystallized in the centrosymmetric triclinic P1[combining macron] space group. The structure of Cs(UO)GeO has a novel oxo-germanate layer composed of germanate tetrahedra and trigonal bipyramids. Two new SBU types, (4·5-A2) and (5-A2) [UGe] pentamers, were found in the structure of Cs(UO)GeO. A(UO)(GeO) (A = Rb, Cs) were synthesized by a high temperature/high pressure (HT/HP) technique, and both structures with oval-shaped 12-membered channels crystallized in the centrosymmetric orthorhombic Pnma space group. The extreme conditions led to the formation of [UGe] tetramers (E), which consist of 7-coordinated U and 5-coordinated Ge. Different synthetic methods of uranyl germanate compounds resulted in a distinct coordination environment of the uranyl cations and a variety of U[double bond, length as m-dash]O and U-O bond lengths, further affecting the dimensionality and types of uranyl units and SBUs. The Raman and IR spectra of the five new phases were collected and analyzed.