Comparison of laser desorption and matrix-assisted laser desorption/ionization for ruthenium and osmium trisbipyridine complexes using Fourier transform mass spectrometry

by Ham, J. E.; Durham, B.; Scott, J. R.

Metal-bipyridine complexes are a vehicle for developing approaches for studying the fluorescence of gas-phase ions; however, conclusions regarding fluorescence behavior depend on explicitly identifying the ionic species in the gas phase. [Ru(bpy)(3)]X-2 and [Os(bpy(3))]X-2, (where bpy = 2,2'-bipyridine and X = Cl or PF6), were studied using direct laser desorption (LD) and matrix-assisted laser desorption/ionization (MALDI) using Fourier transform mass spectrometry (FTMS). LD spectra of the PF, salt of the Ru and Os complexes reveal counterion attachment, fluoride transfer, and significant losses of H for a number of peaks. LD of the chloride salt complexes produced loss of a single bpy ligand, chloride attachment, and losses of H. Spectra of [Ru(bpy(3)]X-2 where X = BF4-, CF3SO3-, and SCN- were also collected using LD and compared with the spectra for Cl-2 and PF6 salts. Regardless of counterion, loss of H is observed in LD spectra. MALDI spectra of the trisbipyridyl complexes using 2,5-dihydroxybenzoic acid (DHB) and sinapinic acid (SA) as the matrix were also obtained. The spectra using SA as matrix show intact molecular ion peaks with very little fragmentation and no counterion attachment. Unlike SA, the spectra obtained using DHB look similar to LD spectra with significant losses of H. Our results are consistent with a reaction scheme for hydrogen loss from a carbon that also involves breaking of the metal-nitrogen bond, rotation of a pyridine ring, and re-formation of an ortho-metallated complex by a metal-C bond. These results demonstrate the importance of ion generation method and the utilization of FTMS for correct characterization of metal poly(pyridyl) complexes.

Journal of the American Society for Mass Spectrometry
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1879-1123; 1044-0305