Fixed frequency dissociation of metal oxide cations and infrared photodissociation studies of metal carbonyl cation systems
Reed, Zachary David
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Metal oxide clusters of the form MnOm + (M=Y,La,In), transition metal carbonyl complexes of the form TM-(CO)n + (TM=Mn,Cu,Au), and mixed vanadium benzene carbonyl complexes of the form V-bz-(CO)n + are produced in the gas phase by laser vaporization in a pulsed nozzle and detected with time-of-flight mass spectrometry. The metal oxide clusters are studied using fixed frequency photodissociation. A limited number of stoichiometries are found for each value of n. Clusters are mass selected and photodissociated using the third harmonic (355 nm) of an Nd:YAG laser. Larger clusters undergo fission to produce certain stable cation clusters. Yttrium and lanthanum oxides clusters of the form MO(M2O3)n + are found to be particularly stable, along with Y6O8+. Density functional theory (DFT) calculations were performed to investigate the structures and bonding of these clusters. The stability of some indium oxide clusters, including In5O4+, In5O4+, and In3O2+ can be understood in terms of Wade’s Rules of electron counting. Other indium oxide clusters with enhanced stability do not follow Wade’s Rules, including In3O1+, and In2O+. The carbonyl and mixed benzene-carbonyl complexes are studied using infrared photodissociation spectroscopy and density functional theory. Mn(CO)6+ has a completed coordination sphere, consistent with its expected 18 electron stability. All manganese carbonyl complexes feature red-shifted υCO. The argon tagged analogues of the small (n=1-6) complexes are studied by IRPD. The spin state of small clusters is observed to gradually decrease as additional ligands are added, from a quintet MnCO+ to a singlet Mn(CO)5+. Copper carbonyl cations are observed to have blue-shifted υCO, demonstrating that they are non-classical carbonyls. Cu(CO)4+ has a completed coordination sphere, in line with the 18 electron rule. All small complexes are observed exclusively as singlets, but some triplet population is observed for n=7,8. This is explained in terms of the increased oscillator strengths of the triplets. Au(CO)n+ is demonstrated to have a completed coordination sphere at n=4, despite having significant reduced binding energy for n=3,4. It is also a non-classical carbonyl. V-bz-(CO)n+ is demonstrated to have two different coordination numbers, with n=3 and n=4. Both feature redshifted υCO. The symmetric CO stretch is strongly activated in these complexes.