Mass spectra of transition-metal

B. Some General Features of the Mass Spectra of Transition Metal Organometallic Compounds. 93... 

The most successful interpretation of mass spectra of transition metal rr-complexes is based on the concept of charge localization on the metal atom. " Ionization energies of the majority of organometaUic molecules are lower than those of the ligands, but differ only slightly from the ionization energies of the free metal atoms. Accordingly, the ionization of transition metal... 

Mass spectra of transition metal clusters do not exhibit any abvmdance anomalies. However, if they are mixed with reactive gases prior to expansion into vacuum, the number of molecules being absorbed exhibits pronovmced size effects. Mass spectra may directly reveal the number of reactive sites on the cluster surface Coj, for example, offers six highly reactive sites towards ammonia. This number tends to increase with cluster size, but local minima are observed at certain cluster sizes, indicating closed shells or subshells in agreement with an icosahedral growth sequence. 

Such a decomposition of MC has been observed in mass spectra of polynuclear metal carbonyl [9] but up to now inorganic chemists could not prepare MC with a sufficient number of transition metal atoms so that they can be stable enough either with or without extra ligands. In the latter case the molecular cluster would obviously have to be supported on a carrier and it would loose its ligands by a thermal treatment under vacuum [10]. A few works have recently appeared in this field [10-12] but it is not proved so far that the frame of the cluster is kept upon thermal treatment however, molecular clusters seem to be obtained by treatment of the finely dispersed particles with the appropriate ligands [10-12]. 

Keto Derivatives of Group IV Organometalloids, 7, 95 Lewis Base-Metal Carbonyl Complexes, 3, 181 Ligand Substitution in Transition Metal ir-Complexes, 10, 347 Literature of Organo-Transition Metal Chemistry 1950-1970, 10, 273 Literature of Organo-Transition Metal Chemistry 1971,11, 447 Literature of Organo-Transition Metal Chemistry 1972, 12, 379 Mass Spectra of Metallocenes and Related Compounds, 8, 211 Mass Spectra of Organometallic Compounds, 6, 273... 

It is well known that certain transition metal organometallic complexes, such as ferrocene, cymantrene (cyclopentadienylmanganese tricarbonyl) and butadieneiron tricarbonyl, and to a lesser extent, benzenechromium tricarbonyl, form organic derivatives and have an extensive derivative chemistry of their own. The parent complexes have already been discussed there follows a summary of the main features observed in the mass spectra of their organic derivatives (Table II, at the end of this section). 

I. Mass Spectra of Fluorocarbon Derivatives of Transition Metals. 113... 

In one of the earliest detailed mass spectroscopic studies with transition metal organometallic compounds, Friedman, Irsa, and Wilkinson 3> showed that in the mass spectra of (C5H5) 2M derivatives the molecular ion was more stable in the covalent 7r-cyclopentadienyls than in the ionic cyclopentadienides. 

Another process of interest in the mass spectra of tris(dimethyl-amino)phosphine derivatives is the elimination of a CH3NCH2 (azapro-pene) fragment. This occurs in ions containing first-row transition metals but no carbonyl groups, e.g. 

While the methyl and silyl cations behave like the proton in only forming a complexes with benzene [279], there is considerable experimental and quantum chemical evidence that alkali metal ions, SF) and NO+ only form n complexes [280-284]. It has been demonstrated by X-ray crystallography that there is a continuous transition in going between these extremes (Fig. 8) [285]. It seems that the more electrophilic the cation is, the closer is the complex to the a form, while the more electron deficient the ring is, the more it seems to tend towards the limiting n complex character. The latter has also been inferred from the appearance of the collisional mass spectra of a variety of aromatic complexes [286]. It is quite surprising that so far we have not discovered any documented examples for which an ion may form both a o complex and a n complex. This... 

In addition to UV/visible flash photolysis and TRIR spectroscopy, other techniques have been used for the detection of transition metal-noble gas interactions in the gas phase. The interaction of noble gases with transition metal ions has been studied in detail. A series of cationic dimeric species, ML" " (M = V, Cr, Fe, Co, Ni L = Ar, Kr, or Xe), have been detected by mass-spectroscopic methods (55-58). It should be noted that noble gas cations L+ are isoelectronic with halogen atoms, therefore, this series of complexes is not entirely unexpected. The bond dissociation energies of these unstable complexes (Table IV) were determined either from the observed diabatic dissociation thresholds obtained from their visible photodissociation spectra or from the threshold energy for collision-induced dissociation. The bond energies are found to increase linearly with the polarizability of the noble gas. 

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