Magnesium Monocationic Complexes:  A Theoretical Study of Metal Ion Binding Energies and Gas-Phase Association Kinetics

Abstract

Bond dissociation energies (BDEs) for complexes of ground state Mg+ (2S) with several small oxygen- and nitrogen-containing ligands (H2O, CO, CO2, H2CO, CH3OH, HCOOH, H2CCO, CH3CHO, c-C2H4O, H2CCHOH, CH3CH2OH, CH3OCH3, NH3, HCN, H2CNH, CH3NH2, CH3CN, CH3CH2NH2, (CH3)2NH, H2NCN, and HCONH2) have been calculated at the CP-dG2thaw level of theory. These BDE values, as well as counterpoise-corrected MP2(thaw)/6-311+G(2df,p) calculations on the Mg+ complexes of several larger ligands, augment and complement existing experimental or theoretical determinations of gas-phase Mg+/ligand bond strengths. The reaction kinetics of complex formation are also investigated via variational transition state theory (VTST) calculations using the computed ligand and molecular ion parameters. Radiative association rate coefficients for most of these systems increase by approximately 1 order of magnitude with every 3-fold reduction in temperature from 300 to 10 K. Several of the largest molecules surveyed-notably, CH3COOH, (CH3)2CO, and CH3CH2CN-exhibit comparatively efficient radiative association with Mg+ (k(RA) > or = 1.0 x 10(-10) cm3 molecule(-1) s(-1)) at temperatures as high as 100 K, implying that these processes may have a considerable influence on the metal ion chemistry of warm molecular astrophysical environments known to contain these potential ligands. Our calculations also identify the infrared chromophoric brightness of various functional groups as a significant factor influencing the efficiency of the radiative association process.

Photochemistry and spectroscopy of small hydrated magnesium clusters Mg+(H2O)n, n = 1–5

“…25 Plowright et al revisited Mg + X and Mg + XY systems and presented structures and vibrational frequencies for Mg + (H 2 O) 1,2 . 9 Dunbar and Petrie simulated the formation of Mg + (H 2 O) by radiative association and found it to be inefficient even at T = 10 K. 27 Berg et al 28,29 produced Mg + (H 2 O) n up to n = 80 and measured black body infrared radiative dissociation (BIRD) rates up to n = 41, as well as intracluster charge transfer (CT) processes and chemical reactions. The existence of a solvent separated ion pair of Mg 2+ and a hydrated electron for n > 17 was proclaimed by Berg et al 29 In the early 2000s, Reinhard and Niedner-Schatteburg investigated the electronic structure of Mg + (H 2 O) n with up to 20 water molecules.…”

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 ).…”

IR Spectroscopy of M+(Acetone) Complexes (M = Mg, Al, Ca): Cation−Carbonyl Binding Interactions

“…Newer studies have applied infrared photodissociation spectroscopy to complexes of these metal cations with ligands such as CO 2 , H 2 O, CH 3 OH, and NH 3 . − In related work, Lisy and co-workers have studied the infrared spectroscopy of alkali cation−acetone complexes in the C−H stretching region . Ab initio calculations have investigated the energetics of bonding and the structures of these metal ion−molecule complexes. ,,,,,− …”