| Abstract
| - The synthesis of bis(carbonyl)mercury(II)undecafluorodiantimonate(V),[Hg(CO)2][Sb2F11]2,and that of thecorresponding mercury(I) salt[Hg2(CO)2][Sb2F11]2are accomplished by the solvolyses ofHg(SO3F)2 or ofHg2F2,treated with fluorosulfuric acid, HSO3F, in liquidantimony(V) fluoride at 80 or 60 °C, respectively, in anatmosphereof CO (500−800 mbar). The resulting white solids are the firstexamples of metal carbonyl derivatives formedby a post-transition element. Both salts are characterized byFT-IR, FT-Raman, and 13C-MAS-NMR spectroscopy.For[Hg(CO)2][Sb2F11],unprecedentedly high CO stretching frequencies (ν̄av= 2279.5 cm-1) and stretchingforceconstant (fr = 21.0 ± 0.1) ×102 Nm-1) are obtained.Equally unprecedented is the1J(13C−199Hg)value of 5219± 5 Hz observed in the 13C MAS-NMR spectrum of the13C labeled isotopomers at δ = 168.8 ± 0.1 ppm.Thecorresponding values (ν̄av = 2247cm-1, fr = (20.4 ±0.1) × 102 Nm-1,1J(13C−199Hg) =3350 ± 50 Hz and2J(13C−199Hg) 850± 50 Hz) are found for[Hg2(CO)2][Sb2F11]2,which has lower thermal stability (decompositionpoint in a sealed tube is 140 °C vs 160 °C for the Hg(II)compound) and a decomposition pressure of 8 Torr at20 °C. The mercury(I) salt is sensitive toward oxidation to[Hg(CO)2][Sb2F11]2during synthesis. Both linearcations (point groupD∞h) are excellentexamples of nonclassical (σ-only) metal−CO bonding. Crystaldata for[Hg(CO)2][Sb2F11]2: monoclinic, space group P21/n;Z = 2; a = 7.607(2) Å; b =14.001(3) Å; c = 9.730(2) Å;β = 111.05(2)°; V = 967.1 Å3;T = 195 K; RF = 0.035 for 1983data (Io ≥2.5σ(Io)) and 143 variables. TheHgatom lies on a crystallographic inversion center. The Hg−C−Oangle is 177.7(7)°. The length of themercury−carbon bond is 2.083(10) Å and of the C−O bond 1.104(12) Årespectively. The structure is stabilized in thesolid state by a number of significant secondary interionic Hg- - -Fand C- - -F contacts.
- The synthesis of[Hg(CO)2][Sb2F11]2,the first thermally stable post-transition metal carbonyl derivate isreported. The compound is characterized by vibrational and13C-MAS-NMR spectra and by X-ray diffraction at 195 K.The cation is linear and features long (2.083(10) Å) Hg−Cshort (1.104(12) Å) CO bonds. Significant secondaryHg- - -F and C- - -F interionic contacts are observed. Allspectroscopic properties like ν̄av(CO) at2279.5 Å, the force constant fr of 21.0 ± 0.1× 102 N m-1, and1J(13C−199Hg) of5219 ± 5 Hz are unprecedentedly high and justify for the first timethe claim that metal to CO π-back-bonding isabsent.
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