Adsorption and Dissociation of Ni(acac)<sub>2</sub> on Iron by Ab Initio Calculations

Corsini, Chiara; Peeters, Stefan; Righi, Maria Clelia

doi:10.1021/acs.jpca.0c05040

Cited by 10 publications

(5 citation statements)

References 28 publications

(33 reference statements)

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“…Cut 2 corresponds to an intermediate situation between cut 1 and cut 3, and its fragmentation energy should also lie between the energies of the other two patterns, according to the results of previous fragmentation analyses carried out for sMoDTC and Ni(acac) 2 . 12 , 34 Indeed, considering the Mo-containing fragment obtained by cut 2 as a doublet leaves the unpaired electron on a sulfur atom, which is more electronegative than molybdenum. This may explain the lower fragmentation energy of cut 2.…”

Section: Resultsmentioning

confidence: 99%

“…We observed that this phenomenon also occurs for the dimeric MoDTC structures and complexes with a similar structure. 30 , 34 This phenomenon is due to the capability of the metallic substrate to stabilize more efficiently the fragments originating by separating the complexes between the chalcogen atoms and the carbon atom of the ligand unit. mMoDTC compounds follow the general rules derived for these small organometallic complexes While the fragmentation of isolated complexes is not favorable, the metallic substrate is able to stabilize the molecular fragments and the dissociation energies become favorable.…”

Section: Resultsmentioning

confidence: 99%

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Experimental and Ab Initio Characterization of Mononuclear Molybdenum Dithiocarbamates in Lubricant Mixtures

et al. 2021

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Molybdenum dithiocarbamates (MoDTCs) are a class of lubricant additives widely employed in automotives. Most of the studies concerning MoDTC take into account the dimeric structures because of their industrial relevance, with the mononuclear compounds usually neglected, because isolating and characterizing subgroups of MoDTC molecules are generally difficult. However, the byproducts of the synthesis of MoDTC can impact the friction reduction performance at metallic interfaces, and the effect of mononuclear MoDTC (mMoDTC) compounds in the lubrication has not been considered yet in the literature. In this study, we consider for the first time the impurities of MoDTC consisting of mononuclear compounds and combine experimental and computational techniques to elucidate the interaction of these impurities with binuclear MoDTC in commercial formulations. We present a preliminary strategy to separate a commercial MoDTC product in chemically different fractions. These fractions present different tribological behaviors depending on the relative amount of mononuclear and binuclear complexes. The calculations indicate that the dissociation mechanism of mMoDTC is similar to the one observed for the dimeric structures. However, the different chemical properties of mMoDTC impact the kinetics for the formation of the beneficial molybdenum disulfide (MoS 2 ) layers, as shown by the tribological experiments. These results help to understand the functionality of MoDTC lubricant additives, providing new insights into the complex synergy between the different chemical structures.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Experimental and Ab Initio Characterization of Mononuclear Molybdenum Dithiocarbamates in Lubricant Mixtures

et al. 2021

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“…A 12 × 12 × 12 K-point grid was used to sample the Brillouin zone of the iridium bulk and the K-point grid was proportionally resized for all the following calculations. We chose not to add any dispersion correction, consistently with our previous investigations [ 56 – 57 ], because these corrections often overestimate the adsorption energies on metallic substrates [ 58 – 59 ]. The process of geometry optimization was stopped when the total energy and the forces converged under thresholds of 1 × 10 −4 Ry and 1 × 10 −3 Ry/bohr, respectively.…”

Section: Methodsmentioning

confidence: 99%

Reconstruction of a 2D layer of KBr on Ir(111) and electromechanical alteration by graphene

Liu¹,

Hinaut²,

Peeters³

et al. 2021

Beilstein J. Nanotechnol.

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A novel reconstruction of a two-dimensional layer of KBr on an Ir(111) surface is observed by high-resolution noncontact atomic force microscopy and verified by density functional theory (DFT). The observed KBr structure is oriented along the main directions of the Ir(111) surface, but forms a characteristic double-line pattern. Comprehensive calculations by DFT, taking into account the observed periodicities, resulted in a new low-energy reconstruction. However, it is fully relaxed into a common cubic structure when a monolayer of graphene is located between substrate and KBr. By using Kelvin probe force microscopy, the work functions of the reconstructed and the cubic configuration of KBr were measured and indicate, in accordance with the DFT calculations, a difference of nearly 900 meV. The difference is due to the strong interaction and local charge displacement of the K+/Br− ions and the Ir(111) surface, which are reduced by the decoupling effect of graphene, thus yielding different electrical and mechanical properties of the top KBr layer.

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“…As seen from the later X-ray photoelectron spectroscopy (XPS) studies, the oxidation state of Co did not notably change during heating. Judging from the structural simplicity of Co(II) acac 2 , and the noted strong acetylacetone smell, this change in color and exotherm should be related to the dissociation of acac – ligands, − which were then protonated and escaped from the system in the form of Hacac gas. In the meantime, consistent with the UV–vis observation, an equimolar amount of TPP and Co(II) acac 2 comixture (red) delayed the exotherm peak to above 125 °C.…”

Section: Resultsmentioning

confidence: 99%

Controlled Triphenylphosphine Reactivity for Epoxy Resin Cure by Transition-Metal β-Diketonates

Liu

Sun

et al. 2022

Chem. Mater.

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Cure kinetics control of epoxy resins is critical for the realization of many structures and processes and is often manipulated by catalyst design. We here show an example of switchable Lewis base catalytic activity through ligand-controlled metal coordination. Divalent first-row transition-metal (Co, Ni, Cu, Zn) β-diketonates with methyl or trifluoromethyl end groups have found distinguished thermal latent curing behaviors in triphenylphosphine (TPP)-catalyzed epoxy resins, namely, a deceleration pattern for metal acetylacetonates (acac2) and an inhibition pattern for metal hexafluoroacetylacetonates (6Facac2). Comparative analysis exposed the major initiation mechanism as phosphine attack on epoxide rings, where the phosphine reactivity was regulated by metal coordination whose strength depends on the original diketone ligands. TPP further stabilized the metal chelates and suppressed their dissociation. Feed ratio studies of Co(II) chelates revealed an equilibrium built upon TPP, metal chelate, and the formed passivated complex through numerical analysis. Further, temperature dependence of the equilibrium constants suggested a reversed metal-base affinity evolution of the two chelates during heating, which determines the equivalent TPP concentration. Chemical and thermal characterizations on the formed complexation states identified structural changes during high-temperature treatment and, along with density functional theory (DFT) calculation, verified the Co–P binding energy that marks the TPP “effectiveness” in each stage to catalyze epoxy cure. It was found that the competition between incoming phosphine and original diketone ligands, depending on the basicity of the latter, dictates the initial relative affinity between metal and phosphine, while beyond phosphine ligand stabilization, the diketone ligand dynamics at elevated temperatures were accompanied by the respective Co–P affinity change. Across different metals, the deviation from the “natural order” in metal-phosphine affinity can also be qualitatively understood from the ligand competition concept, where the same ligand effects on the field stabilization schemes are expected as the distinctions caused by ligand fluorination were consistent throughout d7–d10 metal cations. The knowledge gained from this work could benefit future design of thermal latent catalysts and shed light on the capability of Lewis base reactivity control through adjusting transition-metal coordination spheres.

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Adsorption and Dissociation of Ni(acac)₂ on Iron by Ab Initio Calculations

Cited by 10 publications

References 28 publications

Experimental and Ab Initio Characterization of Mononuclear Molybdenum Dithiocarbamates in Lubricant Mixtures

Experimental and Ab Initio Characterization of Mononuclear Molybdenum Dithiocarbamates in Lubricant Mixtures

Reconstruction of a 2D layer of KBr on Ir(111) and electromechanical alteration by graphene

Controlled Triphenylphosphine Reactivity for Epoxy Resin Cure by Transition-Metal β-Diketonates

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Adsorption and Dissociation of Ni(acac)2 on Iron by Ab Initio Calculations

Cited by 10 publications

References 28 publications

Experimental and Ab Initio Characterization of Mononuclear Molybdenum Dithiocarbamates in Lubricant Mixtures

Experimental and Ab Initio Characterization of Mononuclear Molybdenum Dithiocarbamates in Lubricant Mixtures

Reconstruction of a 2D layer of KBr on Ir(111) and electromechanical alteration by graphene

Controlled Triphenylphosphine Reactivity for Epoxy Resin Cure by Transition-Metal β-Diketonates

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Adsorption and Dissociation of Ni(acac)₂ on Iron by Ab Initio Calculations