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

Abstract

Removal of volatiles at 243 K from solutions of completely dissolved LnF 3 (Ln = La-Dy and Y) and XeF 2 (molar ratio 1 : 3) in anhydrous HF acidified with an excess of BF 3 resulted in [Ln(XeF 2 ) 3 ](BF 4 ) 3 salts. Isolated solids are stable at 298 K and give similar Raman spectra. [La(XeF 2 ) 3 ](BF 4 ) 3 crystallizes in the monoclinic space group C2/m at 150 K. Each La atom is coordinated with three XeF 2 ligands. Six F atoms provided by six bridging BF 4 units, that connect the neighboring La 3 + 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 : XeF 2 = 1 : 1 yielded [Ln(XeF 2 )](BF 4 ) 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 BF 4 units and one XeF 2 ligand. The BF 4 groups interconnect the Ln atoms into two-dimensional layers. With molar ratio LnF 3 : XeF 2 = 1 : 2 and the same synthetic approach, only La yielded [La(XeF 2 ) 2 ](BF 4 ) 3 salt. Prolonged pumping of [Ln(XeF 2 ) n ](BF 4 ) 3 (n = 3, 2, 1) at 298 K or attempts of the isolation at 298 K resulted in products with lower content of XeF 2 or in mixtures of various products. In addition to [Ln-(XeF 2 )](BF 4 ) 3 and LnF 3 /BF 3 products, the [Ln(XeF 2 )]F(BF 4 ) 2 salts (Ln = La, Nd, Sm, Eu, Tb, Dy and Y) also formed. The crystal structures of LaF(HF)(BF 4 ) 2 and LaF(BF 4 ) 2 side products were determined.

Bi(III) stable in the coordination compounds with XeF2 as a ligand

“…The vibrational data for [Ln(XeF 2 ) 3 ](BiF 6 ) 3 (Ln is La, Nd) also showed intense stretching of the Xe−F vibration at 556–559 cm −1 [23] . The splitting of Xe−F t vibrations was also observed in other cases, of which we will mention only two that are more closely related to this case, such as [Nd(XeF 2 ) 2.5 ](AsF 6 ) 3 (υ(Xe−F): 584 cm −1 , 575 cm −1 ) and [Ln(XeF 2 ) 3 ](BF 4 ) 3 (the most intense bands occur in the 568–573 cm −1 region) [14,3] and it is a consequence of weak vibrational coupling and interactions in the solid.…”

“…In [La(XeF 2 ) 3 ](BF 4 ) 3 , the Xe−F b distances range of 2.052–2.058 Å, and the Xe−F t distances are 1.925–1.950 Å. In [Ln(XeF 2 )](BF 4 ) 3 , Xe−F t distances were reported to be quite short (La: Xe−F t : 1.920 Å; Nd: Xe−F t : 1.923 Å) and, on the other hand, Xe−F b are elongated ((La: Xe−F b : 2.093 Å; Nd Xe−F t : 2.115 Å) [3] …”

“…Four F atoms are from XeF 2 molecule and two atoms from AF 6 units are located in the corners of the distorted trigonal prism. In 3 4.975 addition, two bridging XeF 2 molecules and AF 6 units with their F atoms complete the coordination sphere. The XeÀ F b distances in this compound range from 1.971-2.023 Å.…”

“… [2] . A recent report on XeF 2 coordination to lanthanide tetrafluoridoborates revealed the crystal structures of [La(XeF 2 ) 3 ](BF 4 ) 3 and [Nd(XeF 2 )](BF 4 ) 3 [3] . The main reason that the XeF 2 acts as a ligand to the metal center is due to the choice of the metal.…”

“…In most cases, at least those that have been structurally characterized, the counter anion belongs to the octahedral [AF 6 ] À with A = As, Sb, P, etc.. [2] A recent report on XeF 2 coordination to lanthanide tetrafluoridoborates revealed the crystal structures of [La(XeF 2 ) 3 ](BF 4 ) 3 and [Nd(XeF 2 )](BF 4 ) 3 . [3] The main reason that the XeF 2 acts as a ligand to the metal center is due to the choice of the metal. The charge of the metal and its size are the first selection point for the formation of these complex compounds.…”