The first amine-templated layered metal selenates

Abstract

Although a few open-framework metal sulfates and selenites have been synthesized and characterized recently, it has not been possible to prepare the corresponding selenates, probably because of the instability of the +6 oxidation state of Se in alkaline media. We have been able to synthesize, for the first time, organically templated open-framework rare earth selenates with the general formula 0.5[C₂N₂H₁₀][Ln(H₂O)₂(SeO₄)₂] (I) (Ln=La, Nd or Pr) and 0.5[C₄N₂H₁₄][La(SeO₄)₂]·0.5H₂O (II), under hydrothermal conditions in an acidic medium. Crystal data: I (Ln=La): triclinic, space group=Pequation image , Mr=491.91, a=7.0105(8) Å, b=7.3772(9) Å, c=9.526(1) Å, α=82.014(2), β=84.514(2), γ=84.247(2)°, V=483.76(1) ų, Z=2; II: triclinic, space group=Pequation image , Mr=478.91, a=5.94(2), b=7.408(3), c=11.048(2) Å, α=86.899(2), β=75.971(1), γ=79.456(2)°, V=463.7(2) ų, Z=4. Being the first report of complex layered selenates, it is likely to stimulate efforts to synthesize other novel open-framework structures making use of the selenate ion as the building unit.