GAS-PHASE METAL-ION LIGATION - COLLISION-INDUCED DISSOCIATION OF FE(H2O)X+ AND FE(CH4)X+ (X=1-4)

Guided-ion beam mass spectrometry is used to study the collision-induced dissociation (CID) of Fe(H2O)x+ and Fe(CH4)x+ ions, x = 1-4. Ions are produced in a flow tube source to ensure thermalization. By measuring the CID thresholds, we obtain the following 0 K bond dissociation energies (BDEs) for Fe(H2O)x+ Clusters: D-degrees 0[Fe+-(H20)] = 30.6 +/- 1.2 kcal/mol, D-degrees 0[(H20)Fe+-(H20)] = 39.3 +/- 1.0 kcal/mol, D-degrees 0[(H20)2Fe+-(H2O)] = 18.2 +/- 0.9 kcal/mol, and D-degrees 0[(H20)3Fe+-(H20)] = 19.6 +/- 1.2 kcal/mol. Our values for x = 1 and 2 are compared to and contrasted with prior literature measurements and calculations. We also report the first measurements of the BDEs for Fe(CH4)x+ clusters, x = 1-4, obtaining the following 0 K values: D-degrees 0[Fe+-(CH4)] = 13.7 +/- 0.8 kcal/mol, D-degrees 0[(CH4)Fe+-(CH4)] = 23.3 +/- 1.0 kcal/mol, D-degrees 0[(CH4)2Fe+-(CH4)] = 23.6 +/- 1.4 kcal/mol, and D-degrees 0[(CH4)3Fe+-(CH4)] = 17.6 +/- 1.4 kcal/mol. The most surprising observation here is that D-degrees 0[(CH4)2Fe+-(CH4)]exceeds D-degrees-o[(H20)2Fe+-(H20)]. This result and other trends in these BDEs are discussed by examining FeL(x)+ bonding in terms of the nature of the ligand and the electronic structure of the ion.