Osmium structural data

As with earlier sections, there is a lack of structural data on binary xanthates for iron, ruthenium, and osmium, but there are a relatively large number of mixed-ligand complexes, particularly organometallic species. 

RUTHENIUM AND OSMIUM Table 1.15 IR and structural data for 0 NX4Y species... 

Table 3 X-ray structural data for carbene and carbide complexes of ruthenium and osmium porphyrin carbenes...

In the case of electron-poor systems the electron deficit must be compensated by the formation of multiple bonds. Thus, the compound H20s3(CO)io that actually has only 46 electrons should have an Os-Os double bond leading to an isosceles triangular array of osmium atoms. Such a prediction agrees with structural data (Table 2.2) which show indeed one Os-Os distance of 2.60 A, shorter than the other two (2.8 A). 

The complexes of ruthenium and osmium in the same oxidation state are generally similar and are, therefore, treated together the structural (Table 1.3) and vibrational data (Table 1.4) have been set out in some detail to demonstrate halogen-dependent trends. 

Considerable structural information is available on osmium complexes of tertiary phosphines, arsines and stibines (Table 1.13) [152, 157], Comparison with data (mainly obtained from EXAFS measurements) on osmium diarsine complexes (Table 1.14) shows that as the oxidation state increases, osmium-halogen bonds shorten whereas Os-P and Os-As bonds lengthen. Bond shortening is predicted for bonds with ionic character,... 

Monooxo and cis- and trans-6ioxo complexes of ruthenium(VI) and osmium(VI) are known, with the trans-6ioxo species being most common. In general, these complexes are all diamagnetic and are characterized by vibrational spectroscopy and/or X-ray crystallography. One intense metal-0x0 stretch is usually observed for monooxo and trans-dioxo complexes while two metal-oxo stretches, j/s(M(0)2) and J/as(M(0)2), are found for the cw-dioxo species in the IR spectra. The structural and vibrational data are listed in Table 4. 

Reaction of (-)-a-pinene (1) with stoich. RuO /CCl gave a ketoaldehyde (2), probably via a Ru(VI) diester (4). If the reaction is performed using RuO in acetone rather than CCl, the a-ketol (3) is the main product. It is likely that a Ru(VI) diester (4) is involved such a species was isolated and both H and NMR data suggest the structure shown in (Fig. 3.8). An X-ray crystal structure determination was carried out on the osmium analogue of (4) [178]. 

In [59] the authors reported the structure of a tri-osmium complex containing a hydride and clearly stated that a low temperature X-ray diffraction experiment would not be useful to locate the hydride if an accurate absorption correction is not carried out. Curiously, a few years before they had contacted Prof A. Sironi and myself at the University of Milan proposing a low temperature data collection on that compound, with the purpose of locating the not so clearly visible hydride. As evident from [59], we were able to convince them on the real problems connected with the location of hydrogens close to heavy metals. 

Although the third structure type was established for ruthenium pentafluoride (88), the results were based on restricted single-crystal data, giving less accurate molecular dimensions. Full data were used for the structure analysis of the osmium compound (89 ) but the results were still unsatisfactory, because of the predominant scattering by the... 

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