A STUDY OF STEREOCHEMISTRY AND MAGNETIC AND SPECTRAL PROPERTIES OF COORDINATION COMPOUNDS OF NIOBIUM(4) AND TANTALUM(4) CHLORIDES AND BROMIDES AND OF COMPLEX ANIONS NBCL62- AND NBBR62-

Coordination complexes of the types NbX4∙2L and MX4∙B, where M = Nb or Ta; X = Cl or Br; L = acetonitrile, tetra-hydrofuran, tetrahydropyran, or 1,4-dioxane; and B = 2,2’-bipyridyl or 1,10-phenanthroline have been prepared from the tetrahalides. The acetonitrile complexes NbX4∙2CH3CN are useful starting materials for the preparation of the hexahalo salts [(C2H5)4N]2NbX6. The far-infrared spectra (500-200 cm-1) of the solid complexes NbX4∙2L and MX4∙B have been recorded and the metal-halogen stretching frequencies assigned. Interpretation of the latter indicates that these complexes have a cis-octahedral structure; for MX4∙B, the chelating nature of the ligand molecules would in any case make this the most likely structure. The diffuse-reflectance spectra and temperature range magnetic properties of all of the niobium(IV) complexes are compared with related measurements on the “model” octahedral species NbX62-. These spectral measurements allow a fairly straightforward assignment of the halogen(π) → Nb(d) and d ↔ d transitions whereas the behavior of the magnetic properties of the complexes over the temperature range 300-80°K is not generally well understood. © 1969, American Chemical Society. All rights reserved.