Effects of Sequential Ligation of Molybdenum Cation by Chalcogenides on Electronic Structure and Gas-Phase Reactivity†

The molybdenum chalcogenide cations MoXn+ (X = O, S; n = 1−3) are studied by a combined experimental and theoretical approach. The monoligated species MoO+ and MoS+ both have (4Σ-) ground states that formally arise from spin-pairing of Mo+ (6S) with O (3P) and S (3P), respectively. Similarly, the bent triatomic MoX2+ cations exhibit doublet ground states (2A1). The trichalcogenides MoO3+ and MoS3+ also have doublet ground states and exhibit similar C3v-symmetrical structures; however, distinct energetic differences are found in that MoO3+ is much less stable than MoS3+, due to the necessity to ionize a strong Mo−O double bond in neutral MoO3. Sequential addition of chalcogenides to molybdenum goes hand in hand with an increase of the formal oxidation state of the metal. As a result, the ionization energies (IEs) increase with the electronegativity and the number of the chalcogenide atoms added:  IE(MoO) = 7.9 ± 0.3 eV, IE(MoO2) = 8.7 ± 0.3 eV, IE(MoO3) = 11.7 ± 0.3 eV, IE(MoS) = 7.7 ± 0.3 eV, IE(MoS2) = 8...