Coordination of KrF₂ to a Naked Metal Cation, Mg²⁺

Abstract

Examples of coordination compounds in which KrF functions as a ligand are very rare. In contrast, XeF provides a rich coordination chemistry with a variety of main-group and transition metal cations. The reactions of Mg(AsF ) and KrF in HF or BrF solvent have afforded [Mg(KrF ) (AsF ) ] and [Mg(KrF ) (AsF ) ]⋅2 BrF , respectively, the first examples of a metal cation ligated by KrF . Their X-ray crystal structures and Raman spectra show that the KrF ligands and [AsF ] anions are F-coordinated to a naked Mg cation. Quantum-chemical calculations are consistent with essentially non-covalent ligand-metal bonding. These compounds significantly extend the XeF -KrF analogy and the limited chemistry of krypton by introducing a new class of coordination compound in which KrF functions as a ligand towards a naked metal cation.

Syntheses, Structures, and Bonding of NgF2⋅CrOF4, NgF2⋅2CrOF4(Ng=Kr, Xe), and (CrOF4)∞

“…The F t −Ng−F b angles of both NgF 2 ⋅ CrOF 4 adducts are nearly linear [Xe, (E) 179.1(1), (S) 179.81(8)°; Kr, (NS) 179.91(5)°] as observed in other terminally coordinated NgF 2 adducts, for example [BrOF 2 ][AsF 6 ] ⋅ 2XeF 2 [178.8(2)°], [BrOF 2 ][AsF 6 ] ⋅ 2KrF 2 [178.7(2)°], [Mg(KrF 2 ) 4 (AsF 6 ) 2 ] [178.27(7) and 178.95(7)°], and [Hg(KrF 2 ) 8 ][AsF 6 ] 2 [178.3(1)–178.9(1)°] …”

A Homoleptic KrF2 Complex, [Hg(KrF2)8][AsF6]2⋅2 HF

“…This interaction results in polarization of the ligand Kr−F bonds, giving shorter terminal bonds (Kr−F t , 1.822(1)–1.852(1) Å) and correspondingly longer bridge bonds (Kr−F b , 1.933(1)–1.957(1) Å). Similar bond length differences occur for the terminally coordinated KrF 2 molecules of Mg(KrF 2 ) 4 (AsF 6 ) 2 (Kr−F t , 1.817(2)–1.821(2) Å; Kr−F b , 1.965(1)–1.979(1) Å) and F 2 OBr(KrF 2 ) 2 (AsF 6 ) (Kr−F t , 1.840(5), 1.847(4) Å; Kr−F b , 1.933(4), 1.943(4) Å) . These bond length differences are significantly smaller than those observed for the ion‐paired salts of [KrF] + , such as [KrF][AsF 6 ], which has much shorter Kr−F t (1.765(3) Å) and much longer Kr−F b (2.131(2) Å) bonds .…”

“…The coupled Kr−F b stretching modes are assigned to overlapping bands between 449 and 508 cm −1 (calcd; 413–467 cm −1 (B3LYP), 438–492 cm −1 (APFD)), which are also similar to those of Mg(KrF 2 ) 4 (AsF 6 ) 2 (449/460, 467/475, 486, 495 cm −1 ), F 2 OBr(KrF 2 ) 2 (AsF 6 ) (443, 472 cm −1 ), and the Raman‐active symmetric stretching mode (ν 1 , ) of solid KrF 2 at 466.5 cm −1 . The F−Kr−F bending modes are assigned to bands at 238, 262, and 282 cm −1 (calcd; 219–255 cm −1 (B3LYP), 231–286 cm −1 (APFD)) and are also in accordance with those of Mg(KrF 2 ) 4 (AsF 6 ) 2 (227, 293 cm −1 ), F 2 OBr(KrF 2 ) 2 (AsF 6 ) (254, 266, 301 cm −1 ), and the doubly degenerate IR‐active bending mode of gas‐phase KrF 2 (232.6 cm −1 ) …”

“…The calculated vibrational displacements reveal no significant intraligand coupling between the Kr−F t and Kr−F b stretching modes, but significant interligand coupling does occur, as in the cases of Mg(KrF 2 ) 4 (AsF 6 ) 2 and F 2 OBr(KrF 2 ) 2 (AsF 6 ) . The coupled Kr−F t stretching modes are assigned to bands at 540, 543, 554, and 603 cm −1 (calcd; 584–614 cm −1 (B3LYP), 616–645 cm −1 (APFD)).…”

High-Pressure Reactivity of Kr and F2—Stabilization of Krypton in the +4 Oxidation State

“…Due to its higher ionization potential (14.0 eV), krypton is much less reactive and forms compounds only in the +2 oxidation state [7][8][9]. All of these connections are derived from krypton difluoride (KrF 2 ), a compound discovered in 1963 [10][11][12][13], only a year after Bartlett's landmark synthesis of the first xenon compound [14,15].…”