Activation of Methanes by Doubly Charged Metal Dication Complexes in the Gas Phase

A doubly charged metal dication complexes[Mn (Pyridine)4]2+were formed using a combination of the pick-up technique and high energy electron impact, and then held in a cold ion trap where they were excited with tune able UV radiationions and further activated with methane in the gas phase.[Mn (Pyridine)CH4]2+, [Mn (Pyridine)2CH4]2+, [Mn (Pyridine)3CH4]2+, [MnPy2Me2]2+[MnPy3Me2]2+and [Mn (Pyridine)4CH4]2+weresuccessfully identified after the experimental analysis. The binding energies of methane decrease drastically with increasing number of pyridine ligands in the order of [Mn (Pyridine)CH4]2+>[Mn(Pyridine)2CH4]2+>[Mn(Pyridine)3CH4]2+>[Mn(Pyridine)4CH4]2+.The optimised structure of[Mn(Pyridine)4(CH4)]2+indicated C1 symmetry with the methane-manganese ion distance approximately r=2.00 Å.DFT calculated binding energy of methane with Mn2+ was15.13 kJ/mol while the binding energy calculated on the potential energy curve(PEC) was 17.37 kJ/mol. The higher binding energy calculated from the PEC was due to the fact that the charge +2 was assumed for the metal ion in the calculations, but at the optimised geometry the DFT calculated actual charge on the metal ion was (Z=1.43). The calculated binding energy of methane with manganese pyridine dication complex ion was drastically overestimated on the PEC by approximately 15% as compare to DFT.