Effects of intermetallic bonding and lattice interactions. Electronic spectra of group VIA tervalent halides and complex halides

Abstract

Reflectance spectra in the range 4–45kk for a series of halides and complex halides of Cr^III, Mo^III, and W^III are examined and discussed in relation to interactions in the solid state. For chromium(III) fluorides, chlorides, and bromides, the visible and the u.v. spectra can usually be rationalised on the basis of simple crystal-field and MO schemes. Data for chloro- and bromo-molybdenum mononuclear complexes can be treated similarly, but the related molybdenum trihalides exhibit different spectral features. Studies of the binuclear [M₂X₉]^3– species (M = Cr, Mo, or W; X = Cl or Br) as a model system indicate that intermetallic interaction is an important parameter and that it determines the main features of the spectra of these molybdenum and tungsten compounds and binary halides. The spectra of the binuclear complexes especially those of molybdenum are further influenced by the cation. This ‘cation effect’ is attributed to perturbation of the binuclear unit in the lattice.