Laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry of [(Nb(6)X(12))X(2)(H2O)(4)]center dot 4H(2)O, X=Cl or Br

Tetraaquadodeca-mu-halodihalohexaniobium tetrahydrates [(Nb(6)X(12))X(2)(H2O)(4)] . 4H(2)O, X = Cl or Br, were studied using laser desorption/ionization (LDI) Fourier transform ion cyclotron resonance mass spectrometry. Only negative ions were found to form in the gas phase under LDI conditions. The quasimolecular ion, M(-) = [(Nb(6)X(12))X(2)](-) and the fragment ions, [M-X(n)](-), n = 1-3, are the highest abundance ions in the LDI mass spectra, indicating the stability of the core cluster, (Nb(6)X(12)). Clusters with chlorine atoms as ligands show relatively high affinity for an additional chlorine atom, while clusters with bromine atoms as ligands prefer to lose a bromine atom. The results are compared with those of mass spectra of analogous tantalum clusters.