Diarsines structure

Independently, triangulo-Hg3 compounds with stabilizing chelating diphosphine and diarsine ligands have been prepared, 82-387 crystal-structure analyses have been solved (the Hg—Hg bonds, 280 pm, are longer than before), and careful multinuclear NMR spectra measured and analysed. 

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,... 

In sharp contrast to the intensely studied reactions of dipenteles with transition metal compounds, reactions with group 13 metal compounds are almost unknown. Only two diphosphine-borane bisadducts of Type C ([H3B]2[Me4P2], [H2(Br)B]2[Me4P2]) have been synthesized and structurally characterized65 but no diarsine, distibine or dibismuthine adducts. We, therefore, became interested in the synthesis of such compounds, focusing... 

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]. 

In spite of the large number of complexes with diphosphines and diarsines, only a few crystal structures have been determined. Structural data for selected complexes are reported in Table 66. 

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. 

Among chelating P- and As-donors, the diphosphines and diarsines with a general formula 600 are the most propagated. They interact (3.34) with metal salts forming metal-cyclic structures 601 (Sec. 2.2.4.3) ... 

No diarsines or diphosphines show thermochromic behavior similar to that of the distibines and dibismuthines. For example, in the series of dipnictogen compounds A, B, and C illustrated in Scheme 6, the thermochromic distibines and dibismuthines correspond to nonthermochromic diarsines and diphosphines. Structural data are available to compare the three diarsines 51 (46), 52 (57), and 53 (5S) with the corresponding distibines 22 (25,26), 36 (37), and 30 (22). Diarsines 52 and 53 crystallize in gauche conformations as opposed to the trans-staggered conformation of the distibines. In neither case are there intermolecular As---As contacts shorter than 4 A. However, the lack of conformational correspondence makes any comparison tenuous. 

It is in this oxidation state that the known chemistry of the two elements is most different. For rhenium di- and trinuclear cluster species predominate (Section 18-D-5), whereas for Tc there are only a few Tc and no Tc3+ complexes. Mononuclear Tc3+ species do occur. The only simple [MXJ3- complex known for either element is the [Tc(NCS)6]3 ion, but the mer-MCl3(PR3)3, MCl3py3, and [MX2(LL)2]+ complexes with X = halide, NCS , or MeS" and LL a diphosphine or diarsine are important.41 Some of these complexes can be reduced with retention of structure in the II and even I oxidation states.42... 

Few diarsines have been structurally characterized. From X-ray data, crystalline tetramethyldiarsine exists in the trans form. However, Raman spectra of the liquid and electron diffraction and photoelectron spectroscopy data of the vapor indicate both gauche and trans forms present. In the solid state, Ph2AsAsPh2 has an As-As bond length of... 

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