New Open-Framework Mixed-Valence Chromium(III) Cerium(III)/(IV) Sulfate: CrCeIII7CeIV6(HSO4)6(SO4)21\ub775H2O

The title compound, synthesized from CrVI and CeIV species, crystallizes in the space group P63 with a = 19.3015(2), c = 25.2684(4) \uc5, and Z = 2. The structural design of the title compound differs essentially from structures of known mixed-valence cerium compounds which all form three-dimensional networks. In the title compound the cerium atoms, interlinked by sulfate groups, extend to form layers held together by hydrogen-bonding contacts. Perpendicular to these layers there are 10 \uc5 wide channels. One third of the channels host solvent water only, while the other two thirds of the channels also host [Cr(H2O)6]3+ and [Ce(SO4)3(H2O)6]3- units, blocking each of these channels once per unit cell, resulting in 14 \uc5 long voids