Cs3REIIIGe3O9 (RE = Pr, Nd, and Sm-Yb) and Cs8TbIII2TbIVGe9O27: A Rare Example of a Mixed-Valent Tb(III)/Tb(IV) Oxide.

Single crystals of 12 new cesium rare earth germanates crystallizing in two new structure types were grown from a CsCl/CsF flux. Cs3REGe3O9 (RE = Pr, Nd, and Sm-Yb), a new family of germanates that form for almost the entire series of rare earth elements, crystallizes in orthorhombic space group Pna21 with lattice parameters in the following ranges: a = 13.7033(4)-14.022(2) Å, b = 7.0545(2)-7.2405(12) Å, and c = 12.6672(4)-12.836(2) Å. Surprisingly, the Tb reaction yielded both Cs3TbGe3O9 and Cs8Tb3Ge9O27, a rare example of a mixed-valent Tb(III)/Tb(IV) compound. Cs8Tb3Ge9O27 crystallizes in space group P3 with the following lattice parameters: a = 11.2906(4) Å, and c = 7.9605(3) Å. The mixed-valent oxidation state of Tb was confirmed by structure solution, bond-valence sums, X-ray photoelectron spectroscopy data, and magnetic data. Optical and magnetic properties are reported for both sets of compounds.