New Insights into Solvolysis and Reorganization Energy from Gas-Phase, Electrochemical, and Theoretical Studies of Oxo-Tp*Mo^V Molecules

Abstract

Molecules of the general form Tp*MoO(OR)2 (where Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate and (OR)2 = (OMe)2, (OEt)2, and (OnPr)2 for alkoxide ligands, and (OR)2 = O(CH2)3O, O(CH2)4O, and O[CH(CH3)CH2CH(CH3)]O for diolato ligands) were studied using gas-phase photoelectron spectroscopy, cyclic voltammetry, and density functional theory calculations to examine the effect of increasing ligand size and structure on the oxo-molybdenum core. Oxidation potentials and first ionization energies are shown to be sensitive to the character of the diolato and alkoxide ligands. A linear correlation between the solution-phase oxidation potentials and the gas-phase ionization energies resulted in an unexpected slope of greater than unity. Density functional theory calculations indicated that this unique example of a system in which oxidation potentials are more sensitive to substitution than vertical ionization energies is due to the large differences in the cation reorganization energies, which range from 0.2 eV or less for the molecules with diolato ligands to around 0.5 eV for the molecules with alkoxide ligands.

Intermolecular Effects on the Hole States of Triisopropylsilylethynyl-Substituted Oligoacenes

“…In general, the polarization of surrounding molecules in the bulk stabilizes the ground state of a cation much more than that of the neutral molecule in the solid. Thus the ionization energy (which is the energy of transition from the neutral molecule to the cation) measured in the gas phase is generally larger than the ionization energy measured in the solid phase . The lowered energy of the first ionization band going from the gas phase to the solid phase is observed for molecules 1 − 3 (see Figure ), but the amount of this lowering is different for each molecule.…”

Scorpionate Complexes as Models for Molybdenum Enzymes

“…Post‐2000 investigations have focused on scorpionate salts, [Tp*MoOCl(OAr)] and [Tp*MoO(OR) 2 ] (OAr = para ‐phenolate derivative; R = alkyl, aryl) complexes,, [Tp*MoO(bdt)] and its derivatives 37 ,, [Tp*MoO(qdt)] (qdt = quinoxaline‐2,3‐dithiolate),, [Tp*Mo(NO)(bdt)] and its derivatives, and [Cp 2 M(bdt)] (M = Ti, V, Mo) , , . Many complexes have been crystallographically characterized, the structure of [Tp*MoO(qdt)] (Figure ) being typical of oxido‐Mo V Tp* species.…”

“…Gas‐phase PES has been a popular technique for investigating ligand, “electronic buffer” and “fold angle” effects in these compounds. Thus, while ligand variations have little effect on the gross geometric and electronic structures of [Tp*MoO(dithiolene)] complexes they do influence redox potentials and gas phase ionization energies due to variations in the (inter‐related) energy of ψ xy a′ and the effective nuclear charge of the metal . For example, [Tp*MoO(qdt)] exhibits a more positive reduction potential and higher first ionization energy than [Tp*MoO(tdt)] and this is ascribed to the presence of a greater effective Mo nuclear charge and the lowering of ψ xy a′ in [Tp*MoO(qdt)] on account of weaker charge donation from qdt.…”

Metal–Sulfur Valence Orbital Interaction Energies in Metal–Dithiolene Complexes: Determination of Charge and Overlap Interaction Energies by Comparison of Core and Valence Ionization Energy Shifts

“…For instance, the gas-phase ionization energy of a molecule is the major determining factor of the solution oxidation potential. 36,37 This study focuses on experimental energy measurements that are true differences in total energy between molecular electronic states, using the language of molecular orbitals.…”