Gas-Phase Bond Strength and Atomic Connectivity Studies of the Unsymmetrical Two-Center Three-Electron Ion, [Et₂S∴SMe₂]⁺

A computational and experimental study of the unsymmetrical 2c−3e bond in [Et 2 S∴SMe 2 ] + is presented. For the first time, MS/MS collision-induced dissociation experiments provide strong experimental support of the atomic connectivity in a gas-phase S∴S 2c−3e association adduct. The strongest peak in the collision-induced dissociation spectrum corresponds to Et 2 S +, consistent with the lower ionization potential of Et 2 S compared to Me 2 S and the proposed structure. High-pressure equilibrium mass spectrometry experiments yield a reaction enthalpy of −104 kJ/mol for the equilibrium reaction Et 2 S + + Me 2 S ⇄ [Et 2 S∴SMe 2 ] + at 506 K. Correcting this value to 0 K using ab initio molecular parameters results in a bond energy of 107 kJ/mol which can be compared to a calculated value of 107.9 kJ/mol at the B3LYP/6-31G(d)//B3LYP/6-31G(d)+ZPC level. Studies on a competing reaction, Et 2 S + + Et 2 S ⇄ [Et 2 S∴SEt 2 ] +, yield an experimental bond enthalpy of 119 kJ/mol at 506 K and a calculated bond energy of 121.3 kJ/mol, in excellent agreement with previously reported values.