Theoretical Study on the Intracluster Elimination Channels for Mg⁺(CH₃OH), Ca⁺(CH₃OH), Mg⁺(NH₃), and Ca⁺(NH₃)

Abstract

The intracluster elimination reactions in solvated alkaline earth metal monocation clusters, M (+)L n , are known to be size-dependent, indicating links between chemical reactivity and the solvation environment controlled by the cluster size. For the methanol and ammonia clusters, there are a number of competing elimination channels involving the breaking of O-H, C-H, O-CH 3, or N-H bond. In this report, we focus on the four clusters with only one solvent molecule and systematically map out the reaction paths and intermediates. The interaction between the metal ion and the departing H atom or CH 3 group varies considerably, depending on the interaction between the metal ion and the remaining group. The understanding of the nature of these interactions and the evaluation of various theoretical levels in treating these reactions provide a solid base for the investigation of the solvation effects on the chemical reactivity of the larger clusters.

Reductions of Oxygen, Carbon Dioxide, and Acetonitrile by the Magnesium(II)/Magnesium(I) Couple in Aqueous Media: Theoretical Insights from a Nano-Sized Water Droplet

“…The actual roles of Mg(I) in chemical reactions are largely unexplored probably because detail experimental investigation of its chemical properties is challenging because of its metastable characters in condensed phases. Isolation of ions in the gas phase inside a mass spectrometer provides a great opportunity to examine the reactivity of transient intermediates on the molecular level. − Although the subvalent Mg •+ is unstable in the condensed phases, gas-phase [Mg(H 2 O) n ] •+ clusters are isolable and exhibit rich redox chemistry that has attracted much experimental − and theoretical − interests in the past two decades. The solvation structure of [Mg(H 2 O) n ] •+ has been well-characterized; each cluster consists of a Mg 2+ and a hydrated electron solvated out from the 3 s orbital of the original Mg •+ center (reaction ). ,− The solvated electron can reduce a water molecule to liberate a hydrogen atom, leaving the hydroxide ion solvated in the cluster (reaction ).…”

Solvation Effects on the Intracluster Elimination Channels in M+(L)n, where M+ = Mg+ and Ca+, L = CH3OH, and NH3, and n = 2−6

“…The choice of method is based on our two previous studies: one on the geometrical and electronic structures for M + (L) n , with M = Mg + and Ca + , L = CH 3 OH and NH 3 , and n = 1−6 and the other on the elimination channels of the simplest clusters with n = 1 . Systematic comparisons among post-Hartree−Fock and DFT methods, with varying basis set size, indicate that for the Mg clusters, B3LYP/6-31+G* is a very good choice between computational cost and accuracy.…”

“…In a previous report, we have studied the elimination channels in M + (L), where M + is either Mg + or Ca + , and L is either CH 3 OH or NH 3 . They are the first members of the corresponding solvation cluster series, M + (L) n , each of which contains a solute (the metal ion), an electron (on the singly occupied molecular orbital, SOMO), and solvent molecules. − They are the model systems in which the solvation of the electron and the solute could lead to dramatic changes in chemical reactivity. − Experimentally, it is known as the “size-dependent effect”: an elimination channel (such as H or CH 3 elimination in M + (CH 3 OH) n ) is switched on and then off as the number of solvents increases.…”

“…Both the transition structures and intermediates have been carefully mapped out. The interaction between the departing atom H or group CH 3 and the metal ion varies in strength, depending on which bond is broken …”

“…Broadly speaking, one would expect a similar trend of more stabilization for the elimination product with increasing number of solvent molecules. However, the substitution of the solvent water by methanol or ammonia does introduce changes to the cluster reactivities . The interaction between the departing H (or CH 3 ) and the metal ion is more complicated and more significant.…”