Reversible Topotactic Hydration and Dehydration of an Europium Complex [1]

Solid samples of the salt Eu〈L_OEt〉₂(H₂O)₂]BF₄, (〈L_OEt〉 = CoCp{P(OEt)₂O}₃]) may be reversibly dehydrated under very mild conditions to give the corresponding mono aqua complex Eu〈L_OEt〉₂(H₂O)]BF₄. The conversion can be monitored by single crystal x-ray diffraction. In the course of the reaction the crystallinity of the substance is retained: both compounds crystallize in space group P2₁/c with similar lattice constants and essentially the same packing arrangement. The cations show the expected change in the Eu coordination geometry with longer metal-ligand distances for the higher coordinated Eu atoms in the diaqua complex. The crystalline-state reaction is facilitated by a suitable morphology.