Ionization Energies and Redox Potentials of Hydrated Transition Metal Ions: Evaluation of Domain-Based Local Pair Natural Orbital Coupled Cluster Approaches

Hydrated transition metal ions are prototypical systems that can be used to model properties of transition metals in complex chemical environments. These seemingly simple systems present challenges for computational chemistry and are thus crucial in evaluations of quantum chemical methods for spin-state and redox energetics. In this work, we explore the applicability of the domain-based pair natural orbital implementation of coupled cluster (DLPNO-CC) theory to the calculation of ionization energies and redox potentials for hydrated ions of all first transition row (3d) metals in the 2+/3+ oxidation states, in connection with various solvation approaches. In terms of model definition, we investigate the construction of a minimally explicitly hydrated quantum cluster with a first and second hydration layer. We report on the convergence with respect to the coupled cluster expansion and the PNO space, as well as on the role of perturbative triple excitations. A recent implementation of the conductor-like polarizable continuum model (CPCM) for the DLPNO-CC approach is employed to determine self-consistent redox potentials at the coupled cluster level. Our results establish conditions for the convergence of DLPNO-CCSD(T) energetics and stress the absolute necessity to explicitly consider the second solvation sphere even when CPCM is used. The achievable accuracy for redox potentials of a practical DLPNO-based approach is, on average, 0.13 V. Furthermore, multilayer approaches that combine a higher-level DLPNO-CCSD(T) description of the first solvation sphere with a lower-level description of the second solvation layer are investigated. The present work establishes optimal and transferable methodological choices for employing DLPNO-based coupled cluster theory, the associated CPCM implementation, and cost-efficient multilayer derivatives of the approach for open-shell transition metal systems in complex environments

Incoherent Quasielastic Neutron Scattering Study of the Relaxation Dynamics in Molybdenum-Oxide Keplerate-Type Nanocages

Faraone A, Fratini E, Garai S, et al. Incoherent Quasielastic Neutron Scattering Study of the Relaxation Dynamics in Molybdenum-Oxide Keplerate-Type Nanocages. The Journal of Physical Chemistry C. 2014;118(24):13300-13312.The single-particle relaxation dynamics of hydrogen atoms in different oxomolybdate Keplerate-type nanocages characterized by a (metal)(30) icosahedron and a size of approximate to 2.5 nm were studied using incoherent quasielastic neutron scattering. Measurements were performed on a compound with a {Mo72Cr30} nanocage containing internal acetate ligands and a sodium cation coordinated to 12 water molecules. Because of the presence of the methyl groups of the acetate ligands, the related cavity is mostly hydrophobic and represents an interesting model system for investigating the properties of water molecules under confined conditions in contact with hydrophobic surfaces. The single-particle dynamics of both the methyl groups and the water molecules inside the cavity were studied and characterized to. be thermally activated processes. The volume explored by the hydrogen atoms during their motions was also determined. Elastic scan measurements of the {Mo72Cr30} cage, in comparison with the {Mo72V30} cage, which has the same skeletal structure as {Mo72Cr30} but a hydrophilic interior, have allowed an investigation into the vibrational dynamics of the cages themselves and the determination of the effect of the cage polarity