Structural and vibrational characterization of [KrF][AuF_6] and alpha-[O_2][AuF_6] using single crystal X-ray diffraction, Raman spectroscopy and electron structure calculations

摘要

The salt [KrF][AuF_6] has been prepared by the direct oxidation of gold powder in anhydrous HF at 20 deg C using the potent oxidative fluorinating agent KrF_2. the KrF~+ salt readily oxidizes molecular oxygen at ambient temperature to yield [O)2][AuF_6]. Variable temperature Raman spectroscopy has been used to identify a reversible phase transition in [O_2][AuF_6], which occurs between -114 and -118 deg C. Single crystal X-ray diffraction has been used to characterize the low-temperature, alpha-phase of [O_2][AuF_6]. The phase transition is attributed to ordering of the O_2~+ cation in the crystal lattice, which is accompanied by minor distortions of the AuF_6~- anion. The alpha-phase of [O_2][AuF_6] crystallizes in the triclinic sapce group P1, with a=4.935(6) A, b=4.980(6) A, c=5.013(6) A, alpha=101.18(1) deg, beta=90.75(2) deg, gamma=101.98(2) deg, V=342.97A~3, Z=1, and R_1=0.0481 at -122 deg C. The structure of the precursor, [KrF][AuF_6], has also been determined by single crystal X-ray diffraction and crystallizes in the monoclinic space group Cc with a=7.992(3) A, b=7.084(3) A, c=10.721(4) A, beta=105.58(1) deg, V=584.8(4) A~3, Z=4 and R_1=0.0389 at -125 deg C. The KrF~+ and AuF_6~- ions interact by means of a F-Kr…F-Au fluorine bridge that is bent by 125.3(7) deg about the bridge fluorine. The Kr-F_t and Kr…F_b bond lengths in [KrF][AuF_6] were determined to be 1.76(1) and 2.15(1) A, respectively. The energy minimized structures of the [KrF][AuF_6] ion-pair and the AuF_6~- anion have been determined at the Hartree-Fock (HF), MP2 and local density functional (LDF) levels of theory. These calculations have also been used to assign the vibrational spectrum of the [KrF][AuF_6] ion-pair in greater detail and to reassign the vibrational spectrum of the AuF_6~- anion.