Surfaces of a Colloidal Iron Nanoparticle in Its Chemical Environment: A DFT Description

Describing and understanding surface chemistry on the atomic scale is of primary importance in predicting and rationalize nanoparticle morphology as well as their physical and chemical properties. Here we present the results of comprehensive density functional theory studies on the adsorption of several small organic species, representing the major species (H₂, Cl₂, HCl, NH₃, NH₄Cl, and CH₃COOH), present in the reaction medium during colloidal iron nanoparticle synthesis on various low-index iron surface models, namely, (100), (110), (111), (211), and (310). All of the tested ligands strongly interact with the proposed surfaces. Surface energies are calculated and ligand effects on the morphologies are presented, including temperature effects, based on a thermodynamic approach combined with the Wulff construction scheme. The importance of taking into account vibrational contributions during the calculation of surface energies after adsorption is clearly demonstrated. More importantly, we find that thermodynamic ligand effects can be ruled out as the unique driving force in the formation of recently experimentally observed iron cubic nanoparticles

Ligand-Field Theory-Based Analysis of the Adsorption Properties of Ruthenium Nanoparticles

The experimental design of improved nanocatalysts is usually based on shape control and is surface-ligand dependent. First-principle calculations can guide their design, both in terms of activity and selectivity, provided that theoretical descriptors can be defined and used in a prescreening process. As a consequence of the Sabatier principle and of the Brønsted–Evans–Polanyi relationship, an important prerequisite before optimizing the catalytic properties of nanoparticles is the knowledge of the selective adsorption strengths of reactants at their surface. We report here adsorption energies of X (H, CH₃) and L (PH₃, CO) ligands at the surface of bare ruthenium nanoclusters Ru_<i>n</i> (<i>n</i> = 55 and 147) calculated at the DFT level. Their dependence on the topology of the adsorption sites as well as on the size and shape of the nanoparticles (NPs) is rationalized with local descriptors derived from the so-called d-band center model. Defining the descriptors involves the determination of the energy of effective d atomic orbitals for each surface atom. Such a ligand field theory-like model is in close relation with frontier molecular orbital theory, a cornerstone of rational chemical synthesis. The descriptors are depicted as color maps which straightforwardly yield possible reactivity spots. The adsorption map of a large spherical hcp cluster (Ru₂₈₈) nicely confirms the remarkable activity of steps, the so-called B₅ sites. The predictive character of this conceptual DFT approach should apply to other transition metal NPs and it could be a useful guide to the design of efficient nanocatalysts bearing sites with a specific activity

Dimeric Gold Bis(carbene) Complexes by Transmetalation in Water

Due to its cost, environmental benefits, and safety advantages, water has become more and more important as a solvent for catalytic reactions and constitutes the best environment for biomedical applications. Therefore, water-soluble and water-stable metal complexes containing strong σ-donor ligands such as N-heterocyclic carbenes (NHCs) are of great interest in modern coordination chemistry. In this paper we present the successful preparation of two new dinuclear gold­(I)–bis­(NHC) complexes in water, by applying the Ag–NHC transfer route. This green synthetic strategy is valuable for gold­(I) compounds involving N-functionalized neutral and dianionic bis­(NHC) ligands. These two water-soluble compounds were analyzed by spectroscopic methods and by X-ray diffraction. Furthermore, ab initio and DFT calculations on the corresponding dinuclear gold complexes illustrate the important influence of the electrostatic environment of the dinuclear entity on the aurophilic interactions and help to understand the molecular arrangement presented in this paper

Dimeric Gold Bis(carbene) Complexes by Transmetalation in Water

Due to its cost, environmental benefits, and safety advantages, water has become more and more important as a solvent for catalytic reactions and constitutes the best environment for biomedical applications. Therefore, water-soluble and water-stable metal complexes containing strong σ-donor ligands such as N-heterocyclic carbenes (NHCs) are of great interest in modern coordination chemistry. In this paper we present the successful preparation of two new dinuclear gold­(I)–bis­(NHC) complexes in water, by applying the Ag–NHC transfer route. This green synthetic strategy is valuable for gold­(I) compounds involving N-functionalized neutral and dianionic bis­(NHC) ligands. These two water-soluble compounds were analyzed by spectroscopic methods and by X-ray diffraction. Furthermore, ab initio and DFT calculations on the corresponding dinuclear gold complexes illustrate the important influence of the electrostatic environment of the dinuclear entity on the aurophilic interactions and help to understand the molecular arrangement presented in this paper

Yttrium Dihydride Cation [YH₂(THF)₂]⁺_<i>n</i>: Aggregate Formation and Reaction with (NNNN)-Type Macrocycles

Monocationic bis­(hydrocarbyl)­yttrium complexes [YR₂(THF)₂]­[A] (R = CH₂SiMe₃, CH₂C₆H₄-o-NMe₂; A = weakly coordinating anion) underwent hydrogenolysis using dihydrogen or phenylsilane to give a mixture of polynuclear solvent-stabilized dihydride cations [YH₂(THF)₂]_<i>n</i>[A]_<i>n</i>. The mixture composition as well as the nuclearity <i>n</i> depended on the starting material, solvent, and reaction conditions. NMR spectroscopic data in solution and X-ray diffraction data suggested that the main product was tetranuclear, although conclusive structural data were not obtained. DFT calculations supported a <i>closo</i>-type tetrahedral [YH₂(THF)₂]₄⁴⁺ core. The hydridic character of these cations was revealed by their reaction with benzophenone to give the bis­(diphenylmethoxy) cation [Y­(OCHPh₂)₂(THF)₄]­[AlR₄]. The reaction of this cluster with the (NNNN)-type macrocycle Me₄TACD under dihydrogen gave the dinuclear tetrahydride dication with quadruply bridging hydride ligands, [Y₂(μ-H)₄(Me₄TACD)₂]­[A]₂, analogous to the previously characterized lutetium derivative. NH-acidic (Me₃TACD)H gave the dinuclear dihydride dication [Y₂(μ-H)₂(Me₃TACD)₂(THF)₂]­[A]₂

Yttrium Dihydride Cation [YH₂(THF)₂]⁺_<i>n</i>: Aggregate Formation and Reaction with (NNNN)-Type Macrocycles

Monocationic bis­(hydrocarbyl)­yttrium complexes [YR₂(THF)₂]­[A] (R = CH₂SiMe₃, CH₂C₆H₄-o-NMe₂; A = weakly coordinating anion) underwent hydrogenolysis using dihydrogen or phenylsilane to give a mixture of polynuclear solvent-stabilized dihydride cations [YH₂(THF)₂]_<i>n</i>[A]_<i>n</i>. The mixture composition as well as the nuclearity <i>n</i> depended on the starting material, solvent, and reaction conditions. NMR spectroscopic data in solution and X-ray diffraction data suggested that the main product was tetranuclear, although conclusive structural data were not obtained. DFT calculations supported a <i>closo</i>-type tetrahedral [YH₂(THF)₂]₄⁴⁺ core. The hydridic character of these cations was revealed by their reaction with benzophenone to give the bis­(diphenylmethoxy) cation [Y­(OCHPh₂)₂(THF)₄]­[AlR₄]. The reaction of this cluster with the (NNNN)-type macrocycle Me₄TACD under dihydrogen gave the dinuclear tetrahydride dication with quadruply bridging hydride ligands, [Y₂(μ-H)₄(Me₄TACD)₂]­[A]₂, analogous to the previously characterized lutetium derivative. NH-acidic (Me₃TACD)H gave the dinuclear dihydride dication [Y₂(μ-H)₂(Me₃TACD)₂(THF)₂]­[A]₂

Yttrium Dihydride Cation [YH₂(THF)₂]⁺_<i>n</i>: Aggregate Formation and Reaction with (NNNN)-Type Macrocycles

Monocationic bis­(hydrocarbyl)­yttrium complexes [YR₂(THF)₂]­[A] (R = CH₂SiMe₃, CH₂C₆H₄-o-NMe₂; A = weakly coordinating anion) underwent hydrogenolysis using dihydrogen or phenylsilane to give a mixture of polynuclear solvent-stabilized dihydride cations [YH₂(THF)₂]_<i>n</i>[A]_<i>n</i>. The mixture composition as well as the nuclearity <i>n</i> depended on the starting material, solvent, and reaction conditions. NMR spectroscopic data in solution and X-ray diffraction data suggested that the main product was tetranuclear, although conclusive structural data were not obtained. DFT calculations supported a <i>closo</i>-type tetrahedral [YH₂(THF)₂]₄⁴⁺ core. The hydridic character of these cations was revealed by their reaction with benzophenone to give the bis­(diphenylmethoxy) cation [Y­(OCHPh₂)₂(THF)₄]­[AlR₄]. The reaction of this cluster with the (NNNN)-type macrocycle Me₄TACD under dihydrogen gave the dinuclear tetrahydride dication with quadruply bridging hydride ligands, [Y₂(μ-H)₄(Me₄TACD)₂]­[A]₂, analogous to the previously characterized lutetium derivative. NH-acidic (Me₃TACD)H gave the dinuclear dihydride dication [Y₂(μ-H)₂(Me₃TACD)₂(THF)₂]­[A]₂

Yttrium Dihydride Cation [YH₂(THF)₂]⁺_<i>n</i>: Aggregate Formation and Reaction with (NNNN)-Type Macrocycles

Monocationic bis­(hydrocarbyl)­yttrium complexes [YR₂(THF)₂]­[A] (R = CH₂SiMe₃, CH₂C₆H₄-o-NMe₂; A = weakly coordinating anion) underwent hydrogenolysis using dihydrogen or phenylsilane to give a mixture of polynuclear solvent-stabilized dihydride cations [YH₂(THF)₂]_<i>n</i>[A]_<i>n</i>. The mixture composition as well as the nuclearity <i>n</i> depended on the starting material, solvent, and reaction conditions. NMR spectroscopic data in solution and X-ray diffraction data suggested that the main product was tetranuclear, although conclusive structural data were not obtained. DFT calculations supported a <i>closo</i>-type tetrahedral [YH₂(THF)₂]₄⁴⁺ core. The hydridic character of these cations was revealed by their reaction with benzophenone to give the bis­(diphenylmethoxy) cation [Y­(OCHPh₂)₂(THF)₄]­[AlR₄]. The reaction of this cluster with the (NNNN)-type macrocycle Me₄TACD under dihydrogen gave the dinuclear tetrahydride dication with quadruply bridging hydride ligands, [Y₂(μ-H)₄(Me₄TACD)₂]­[A]₂, analogous to the previously characterized lutetium derivative. NH-acidic (Me₃TACD)H gave the dinuclear dihydride dication [Y₂(μ-H)₂(Me₃TACD)₂(THF)₂]­[A]₂

Yttrium Dihydride Cation [YH₂(THF)₂]⁺_<i>n</i>: Aggregate Formation and Reaction with (NNNN)-Type Macrocycles

Monocationic bis­(hydrocarbyl)­yttrium complexes [YR₂(THF)₂]­[A] (R = CH₂SiMe₃, CH₂C₆H₄-o-NMe₂; A = weakly coordinating anion) underwent hydrogenolysis using dihydrogen or phenylsilane to give a mixture of polynuclear solvent-stabilized dihydride cations [YH₂(THF)₂]_<i>n</i>[A]_<i>n</i>. The mixture composition as well as the nuclearity <i>n</i> depended on the starting material, solvent, and reaction conditions. NMR spectroscopic data in solution and X-ray diffraction data suggested that the main product was tetranuclear, although conclusive structural data were not obtained. DFT calculations supported a <i>closo</i>-type tetrahedral [YH₂(THF)₂]₄⁴⁺ core. The hydridic character of these cations was revealed by their reaction with benzophenone to give the bis­(diphenylmethoxy) cation [Y­(OCHPh₂)₂(THF)₄]­[AlR₄]. The reaction of this cluster with the (NNNN)-type macrocycle Me₄TACD under dihydrogen gave the dinuclear tetrahydride dication with quadruply bridging hydride ligands, [Y₂(μ-H)₄(Me₄TACD)₂]­[A]₂, analogous to the previously characterized lutetium derivative. NH-acidic (Me₃TACD)H gave the dinuclear dihydride dication [Y₂(μ-H)₂(Me₃TACD)₂(THF)₂]­[A]₂