Structures of microsolvated transition metal clusters by FT-MS and IRMPD spectroscopy : implications for metal speciation and transport in vapor ore fluids

Abstract

My study mainly focuses on the microsolvation of 3d transition metal clusters, [M2(ClO4)3(H2O)n]+ clusters (M = Zn, Cu, Ni), aiming to provide an insight view on the structural transition of micro-solvated transition metal ions by FTICR-MS, IRMPD spectroscopy and computational chemistry methods. The thesis presents the results of FTICR-MS and IRMPD experiments for three nickel perchlorate clusters, [Ni2(ClO4)3(H2O)4]+, [Ni2(ClO4)3(H2O)5]+, and [Ni5(ClO4)8(OH)(H2O)4]+. In the mass spectra, the di-nuclear nickel perchlorate clusters are the dominant species in the gas-phase accounting for more than 90% of the overall ion abundance. For the IRMPD experiment part, I mainly scanned the symmetric and asymmetric stretching frequencies region of water molecules (3100 cm-1 to 3800 cm-1 wavenumbers) for [Ni2(ClO4)3(H2O)4]+, [Ni2(ClO4)3(H2O)5]+, [Ni5(ClO4)8(OH)(H2O)4]+ and the bending stretch frequencies region of water molecules as well as the vibrations at frequencies region of Cl-O bond (550 cm-1 to 1850 cm-1) for [Ni2(ClO4)3(H2O)4]+ and [Ni2(ClO4)3(H2O)5]+ clusters. A strong red-shift appears in the IR spectra of [Ni2(ClO4)3(H2O)5]+ at 3199 cm-1, indicating a water-water hydrogen bonding structure exists in the gas-phase. I also present the theoretical work of above three nickel perchlorate species after geometry optimization and frequency calculation under M06/aug-cc-pVDZ for Cl, O, H atom and Stuttgart RSC 1997 ECP basis set of nickel atom. I find that no single structure can give rise to all IR bands in experimental IRMPD spectra, and several isomers within an energy range contribute to the IR peaks of IRMPD spectra together. In the case of [Ni2(ClO4)3(H¬2O)4]+ cluster, slight red-shifts are mainly due to hydrogen bonds between water molecules and perchlorate ions in clusters. For [Ni2(ClO4)3(H¬2O)5]+ clusters, one isomer exhibits a strong IR peak at 3196 cm-1 which matches the IR band in experimental IRMPD spectra at 3199 cm-1, illustrating that there is a water-water hydrogen bonding existing in [Ni2(ClO4)3(H-2O)5]+ clusters with a structure that the fifth water molecule attaches to the first water shell around the transition metal core. For the mass measurement on cobalt perchlorate clusters, I observe that di-nuclear clusters are also the dominant species in the gas phase of the nickel perchlorate system comprising a 60% normalized abundance. In the IRMPD measurement of [Co2(ClO4)3(H2O)3]+ clusters, calculated OH symmetric (v1) and asymmetric (v3) stretching frequencies of three waters in [Co2(ClO4)3(H2O)3]+ clusters are in good agreement with experimental OH vibrational frequencies in [Co2(ClO4)3(H2O)3]+ clusters. I also carry out a theoretical study on transition metals (Zn, Cu, Ni) perchlorate clusters, and observe the growth and formation of the second water shell around the core of di-nuclear transition metal perchlorate ions with a growing number of water molecules. The growth of [Ni2(ClO4)3(H2O)n]+ and [Zn2(ClO4)3(H2O)n]+ prefers to generate symmetrical structures with water molecules positioning on both sides of [M2(ClO4)3]+ core. Strong water-water hydrogen bonds appear as the seventh water molecules interacted with first water shell consisting of six water molecules, and three transition metals undergo a transition from octahedral to tetrahedral coordination. Word Count: 475