X-RAY PHOTOELECTRON-SPECTRA OF INORGANIC MOLECULES .22. HALOGEN CORE ELECTRON-BINDING ENERGIES OF LOW OXIDATION-STATE MOLYBDENUM BROMIDE AND MOLYBDENUM IODIDE CLUSTERS AND NIOBIUM AND TANTALUM CHLORIDES CONTAINING THE [M6CL12]N+ CORES

The Br 3p and I 3d binding energy spectra of α-molybdenum bromide and iodide, (Mo6X8)X4, and the bromide derivatives (Mo6Br8)Br4L2 and (Et4N)2[(Mo6Br8)X6], where X=Cl or Br, show that bridging (Xb) and terminal (Xt) halogen environments are readily differentiated by X-ray photoelectron spectroscopy (XPS). Values of ΔE(Xb-Xt) were in the range of 1.8-2.4 eV for the bromide complexes and 1.3 eV for (Mo6I8)I4. XPS data for the complex (Bu4N)2Mo4I11 show the presence of two sets of I 3d3/2, 5/2 doublets which differ in binding energy by 1.2 eV. The energies and relative intensities of these latter peaks are in accord with a stoichiometric ratio Ib:It equal to 7:4. These studies constitute the first examples of the use of XPS to successfully distinguish different halogen environments in transition-metal bromides and iodides and their complexes. The Cl 2p spectra of the niobium and tantalum chloride clusters which contain the (M6Cl12)n+ cores have also been measured and show that, like Re3Cl9 and (Mo6Cl8)Cl4 and their derivatives, the binding energy order is Clb>Clt, with ΔE(Clb-Clt) being between 1.4 and 2.1 eV. © 1979, American Chemical Society. All rights reserved.