Diarsines complexes

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,... 

These bis(diarsine) complexes show remarkable behavior in solution. When the anion is perchlorate, they are 2 1 electrolytes in solvents such as nitrobenzene (118b, 119), and the formation of solvated cations [M(DA)2]2+... 

When the apparently penta-coordinated diarsine complexes just described are dissolved in solvents more polar than nitrobenzene, they tend to dissociate into halide ions and bivalent cations, thus becoming 2 1 electrolytes (119). The effect is most marked with the platinum compounds. It has been shown that solvation effects might be less with platinum than with palladium, and so, other things in the equilibria being equal, it can also be concluded that the bonding of further ligands by a square-planar complex is much weaker with platinum than with palladium. Square-planar nickel complexes are of course the most ready to take up further ligands. 

Of the diarsine complexes partly described in Section IV,D,2,b, the perchlorates, [M(DA)2X]C104, arc isomorphous (119a). Full details of the structure have not been published, but it seems very likely that the cations contain essentially penta-coordinated metal atoms. 

Enemark, J. H., Feltham, R. D., Riker-Nappier, J., and Bizot, K. F. (1975). Stereochemical control of valence. IV. Comparison of the structures and chemical reactivities of five-and six-coordinate diarsine complexes of the cobalt nitrosyls CoNO) group. Inorg. Chem. 14, 624-632. 

Examples of monomeric Mo11 complexes are much less common. It has been demonstrated that the [Mo(CN)7]5 ion has a pentagonal bipyramidal structure. Other examples are nitrile (i.e. isocyanide) complexes [Mo(CNR)7]2+, which has a capped trigonal prismatic structure, and the diarsine complex [Mo(diars)2X2]. 

P NMR spectroscopy.53 Steric factors account for the different coordination modes, while the influence of electronic factors is evidenced by the difference in structure between analogous palladium(II) and platinum(II) compounds, for example, the thiocyanates are N- and S-bonded in [Pd(NCS)(SCN)(diars)], but only S-bonded in [Pt(SCN)2(diars)].54 These and other diphosphine or diarsine complexes of palladium(II) with thio- or seleno-cyanate ligands are further discussed in Section 51.8.2.6. 

The first diarsine complex with a known coordination number of eight was prepared from o-phenylenedimethyldiarsine 110-114) and titanium tetrachloride in THE. Similarly prepared (Zr,Hf )0l4 2(diarsine) compounds are white, insoluble products. They do not melt but rather decompose (290° and 284°C for zirconium and hafnium, respectively). 

The strong infrared bands for the methyl rocking mode at 884 and 846 cm and for the C-H deformation at 741 cm of the free ligand appear 20 cm higher in the complexes, which is consistent with bidentate chelation. The zirconium and hafnium bis(diarsine) complexes are isomorphous with the TiX4-2diarsine complex for which the crystal structure is known (Fig. 2). In this structure the point symmetry is... 

The neutral diarsine complexes Tc (diars)2X2]° (X=Cl,Br,I) are long known and arc obtained by reducing the Tc(IlI) compounds [Tc(diars)2X2]X with H PO . The yellow to brown non-electrolytes are slightly soluble in nitrobenzene and nitro-methane. The magnetic moment of the complexes range from 1.9 to 2.1 M.B. at 20 °C. TTiey are isostructural with the analogous complexes of Re(ll) 79.412. ... 

Os(N3)2(PMe2Ph)4, is a white material made from Os(PMe2Ph)4Cl2 and NaN, is at 2050cm . The diarsine complex Os(N3)(diars)2Cl is known, prepared from trans-[Os(NO)diars2Clf + and N2H4-HC1 with HQ it gives the yellow [Os(N2)(diars)2Cl]Cl. ... 

An -ray crystal structure of the diarsine complex (8), prepared by the reaction of iodine in methylene chloride with the corresponding complex (L-L)W(CX> 4, shows the seven-co-ordinate tungsten as a distorted capped octahedron , one of the CO ligands forming the cap, and the CsAssW ring being puckered. 

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