Xenon-metal bonds

The methodology for studying M-Ng complexes in the gas phase is essentially the same as the TRIR method for liquified noble gases a pump pulse photolyzes a metal carbonyl ion and the fragment is detected with the aid of a continuous IR laser. In these experiments helium is utilized as the standard buffer gas. A xenon complex may be detected by alteration in the spectrum and kinetics on addition of xenon. Since the spectra are free of solvent effects, the effect of coordination should be more easily discerned than in the liquid phase. This method has been used to study M(CO)sXe (M = Cr, Mo, W) and W(CO)sKr. Metal-xenon bond energies of ca. 35 kJmol are deduced from the kinetics of reaction with CO. The variation between metals in comparable to the error bars, about 4 kJ mol . The W-Kr bond energy is estimated to be less than 25 kJmol . ... 

Compounds containing metal-xenon bonds have been known only since 2000. The first example was the square... 

The first detection of compounds containing metal-xenon bonds (Fe(CO)4Xe and M(CO)sXe with M = Cr, Mo, W) was in the 1970s and involved matrix isolation studies. Since 2000, a number of fully isolated and characterized compounds containing Au-Xe or Hg-Xe bonds have been known, but even the most stable of these compounds decomposes at 298 K with loss of Xe. Their isolation depends upon the solvent and counter-ion being a weaker base than Xe(0). The first example was the square planar [AuXe4] cation (av. Au—Xe = 275 pm). It is produced when AUF3 is reduced to Au(II) in anhydrous HF/SbFs in the presence of Xe (equation 18.24). 

The first metal-xenon compound with direct Au—Xe bonds has been reported by Seidel and Seppelt1027-1029 [Eq. (4.252)]. The salt crystallizes in two crystallographic modifications differing in cation-anion interactions. In each form the cation is a regular square. In the triclinic modification the Au—Xe bond lengths are between 2.7330 A and 2.7779 A and there are three weak interionic contacts (Au—F... 

Key properties of noble gases are summarized in Table 1 other properties are in refs. 6 and 11. The formation and detection of M-Ng bonds provide many of the same challenges as for transition metal-alkane bonds. Comparison of spectra and energetics of species such as Cr(CO)5Xe and Cr(CO)s(alkane) points to further similarities in bond enthalpies. Recent reviews tackle complexes of alkanes in detail . Since investigations of alkane complexes are more frequent than those of xenon complexes, we may use these results to anticipate the formation of further M-Ng bonds [e.g., to HMn(CO)4]. 

In the past 40 years, compounds have been isolated in which xenon is bonded to several nonmetals (N, C, and Cl) in addition to fluorine and oxygen. In the year 2000, it was reported [Science, Volume 290. page 117) that a compound had been isolated in which a metal atom was bonded to xenon. This compound is a dark red solid stable at temperatures below -40°C it is believed to contain the [AuXe4F+ cation. 

Duncanson (i) of the molecular orbital bonding concepts of Dewar (2), which he developed to explain the structure of Ag+-olefin complexes, led to the suggestion that ethylene is symmetrically coordinated to the metal. Platinum, atomic number 78, has the electronic configuration of the xenon core (Is 2s 2p 35 3p 3d Z = 54), then... 

The mercury atom is smaller than expected from the zinc-cadmium trend and is more difficult to ionize than the lighter atoms. In consequence the metal-metal bonding in mercury is relatively poor, resulting in the element being a liquid in its standard state. This almost Group 18 behaviour of mercury may be compared to that of a real Group 18 element, xenon, which has first and second ionization energies of 1170 and 2050 kJ mol. ... 

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