XeF2 Coordination to La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Y in Rare-Earth Metal(III) Tetrafluoridoborates

Removal of volatiles at 243 K from solutions of completely dissolved LnF(3) (Ln=La-Dy and Y) and XeF2 (molar ratio 1 : 3) in anhydrous HF acidified with an excess of BF3 resulted in [Ln(XeF2)(3)](BF4)(3) salts. Isolated solids are stable at 298 K and give similar Raman spectra. [La(XeF2)(3)](BF4)(3) crystallizes in the monoclinic space group C2/m at 150 K. Each La atom is coordinated with three XeF2 ligands. Six F atoms provided by six bridging BF4 units, that connect the neighboring La3+ atoms into columns, complete the nine-fold coordination of each La atom. Chemical reactions carried out in the same way but with molar ratio LnF(3) : XeF2=1 : 1 yielded [Ln(XeF2)](BF4)(3) salts (La - Nd). Crystal structures of La and Nd salts are isotypic and crystallize in the monoclinic space group P2(1)/m at 150 K (La) and 200 K (Nd). Each Ln center is coordinated by nine fluorine atoms provided by eight BF4 units and one XeF2 ligand. The BF4 groups interconnect the Ln atoms into two-dimensional layers. With molar ratio LnF(3) : XeF2=1 : 2 and the same synthetic approach, only La yielded [La(XeF2)(2)](BF4)(3) salt. Prolonged pumping of [Ln(XeF2)(n)](BF4)(3) (n=3, 2, 1) at 298 K or attempts of the isolation at 298 K resulted in products with lower content of XeF2 or in mixtures of various products. In addition to [Ln(XeF2)](BF4)(3) and LnF(3)/BF3 products, the [Ln(XeF2)]F(BF4)(2) salts (Ln=La, Nd, Sm, Eu, Tb, Dy and Y) also formed. The crystal structures of LaF(HF)(BF4)(2) and LaF(BF4)(2) side products were determined.