Low-spin complexes of Ni2+ with six NH3 and H2O ligands: A DFT–RX3LYP study

Varadwaj, Pradeep R.; Cukrowski, Ignacy; Marques, Helder M.

doi:10.1016/j.theochem.2009.02.001

Cited by 9 publications

(9 citation statements)

References 33 publications

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“…A tight gradient convergence criterion with ultrafine integration grid was specified in these calculations. Similar to our previous experiences with the Ni 2+ complexes, 16,26 we occasionally encountered SCF convergence failures that caused termination of the calculation or, in some cases, produced first order saddle point structures seen from the presence of imaginary frequencies. These SCF convergence problems are not unexpected because of the open-shell nature of Co 2+ ; the interaction of the metal with the ligands can lead to several low-lying electronic states arising from different d orbital occupancies since transition metal ions usually have several near-degenerate ground terms.…”

Section: Computational Detailssupporting

confidence: 76%

“…(The keyword SCF = Fermi was helpful in some cases to avoid SCF convergence failure. ) We have previously 16,26 determined the structure of the free ligands H 2 O and NH 3 in their singlet electronic ground states using the same level of theory and basis set as used in this study for the Co 2+ complexes. The corresponding B3LYP calculations were performed in this work for the free ligands.…”

Section: Computational Detailsmentioning

confidence: 99%

“…The basis set used is adequate for the purpose of this study since we have used basis sets of similar quality before in our studies in transition metal complexes and have found them to describe the molecular and electronic structure of the complexes in a well-defined manner. 16,26 We performed frequency calculations by determining analytically the second derivatives of the UX3LYP or UB3LYP potential energy surfaces with respect to the fixed nuclear coordinates to determine whether each of the minimised structures corresponded to an energy minimum or a saddle point. A tight gradient convergence criterion with ultrafine integration grid was specified in these calculations.…”

Section: Computational Detailsmentioning

confidence: 99%

“…We have continued our exploration 16,26 of the nature of metal-ligand bonding in these complexes by using QTAIM formalism 15 and examining various topological properties at the bond critical points (bcps). The topological parameters, including the electron charge density (r c ), the Laplacian of the charge density (r 2 r c ), the local potential and gradient kinetic energy densities (V c and G c ), and the total energy density (H c ) at the bcp have been used to provide an insight into the bonding in these complexes.…”

Section: Introductionmentioning

confidence: 99%

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The physical chemistry of coordinated aqua-, ammine-, and mixed-ligand Co2+ complexes: DFT studies on the structure, energetics, and topological properties of the electron density

Varadwaj

Marques

2010

Phys. Chem. Chem. Phys.

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Spin-unrestricted DFT-X3LYP/6-311++G(d,p) calculations have been performed on a series of complexes of the form [Co(H(2)O)(6-n)(NH(3))(n)](2+) (n = 0-6) to examine their equilibrium gas-phase structures, energetics, and electronic properties in their quartet electronic ground states. In all cases Co(2+) in the energy-minimised structures is in a pseudo-octahedral environment. The calculations overestimate the Co-O and Co-N bond lengths by 0.04 and 0.08 A, respectively, compared to the crystallographically observed mean values. There is a very small Jahn-Teller distortion in the structure of [Co(H(2)O)(6)](2+) which is in contrast to the very marked distortions observed in most (but not all) structures of this cation that have been observed experimentally. The successive replacement of ligated H(2)O by NH(3) leads to an increase in complex stability by 6 +/- 1 kcal mol(-1) per additional NH(3) ligand. Calculations using UB3LYP give stabilisation energies of the complexes about 5 kcal mol(-1) smaller and metal-ligand bond lengths about 0.005 A longer than the X3LYP values since the X3LYP level accounts for the London dispersion energy contribution to the overall stabilisation energy whilst it is largely missing at the B3LYP level. From a natural population analysis (NPA) it is shown that the formation of these complexes is accompanied by ligand-to-metal charge transfer the extent of which increases with the number of NH(3) ligands in the coordination sphere of Co(2+). From an examination of the topological properties of the electron charge density using Bader's quantum theory of atoms in molecules it is shown that the electron density rho(c) at the Co-O bond critical points is generally smaller than that at the Co-N bond critical points. Hence Co-O bonds are weaker than Co-N bonds in these complexes and the stability increases as NH(3) replaces H(2)O in the metal's coordination sphere. Several indicators, including the sign and magnitude of the Laplacian of the charge density nabla(2)rho(c), the ratio of the local potential and kinetic energy densities, |V(c)|/G(c), the sign of the total energy density H(c), and the delocalisation index delta(Co,X), X = O, N, are used to show that whilst the metal-ligand bonds are predominantly ionic in nature, they gain covalent character as NH(3) replaces H(2)O, and the Co-N bond is significantly more covalent than the Co-O bond. We have shown that the delocalisation index delta(Co,X), X = O, N, is strongly correlated with the zero-point corrected stabilisation energy E demonstrating that delta can be used as a measure of the bond stability in these complexes.

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Section: Computational Detailssupporting

confidence: 76%

Section: Computational Detailsmentioning

confidence: 99%

Section: Computational Detailsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The physical chemistry of coordinated aqua-, ammine-, and mixed-ligand Co2+ complexes: DFT studies on the structure, energetics, and topological properties of the electron density

Varadwaj

Marques

2010

Phys. Chem. Chem. Phys.

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“…While QTAIM has been able to recover BPs where a classical chemical bond is expected, it has also shown the presence of AILs where steric hindrance is classically expected, thus a debate has ensued discussing the meanings and interpretations of chemical bonds, steric repulsions and the concept of bonding . Despite this controversy, QTAIM has been widely used for the visualization and analysis of all kinds of chemical bonds in a variety of compounds, among them coordination bonds and intramolecular interactions in various metal complexes . For the complexes of Ni II and Zn II with NTA and NTPA, the following was determined: (i) BPs where found for the weak CH•••HC and CH•••O intramolecular interactions in the complexes of NTPA, (ii) the density at the ring critical point (RCP) of a chelating ring appeared to correlate with the differences in the formation constants between 5m‐CR and 6m‐CR complexes, and (iii) the differences in formation constants were attributed to the greater strain incurred during the preorganization of NTPA with the ratio of the strain energy of NTPA:NTA being comparable to the ratio of the formation constants.…”

Section: Introductionmentioning

confidence: 99%

Interacting quantum fragments‐rooted preorganized‐interacting fragments attributed relative molecular stability of the Be^IIcomplexes of nitrilotriacetic acid and nitrilotri‐3‐propionic acid

Cukrowski

Mangondo

2016

J Comput Chem

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A method designed to investigate, on a fundamental level, the origin of relative stability of molecules (or molecular systems in general) using Be II complexes with nitrilotriacetic acid (NTA) and nitrilotri-3-propionic acid (NTPA) as a case study (this is the only known example where a metal ion forms stronger complex with NTPA) is described. It makes use of the primary (self-atomic and diatomic interaction) and molecular fragment energy terms as defined in the IQA/F (Interacting Quantum Atoms/Fragments) framework. An extensive classical-type investigation, focused on single descriptors (bond length, density at critical point, the size of metal ion or coordination ring, interaction energy between Be II and a donor atom, etc.) showed that it is not possible to explain the experimental trend. The proposed methodology is fundamentally different in that it accounts for the total energy contributions coming from all atoms of selected molecular fragments, and monitors changes in defined energy terms (e.g., fragment deformation, inter-and intra-fragment interaction) on complex formation. By decomposing combined energy terms we identified the origin of relative stability of Be II (NTA) and Be II (NTPA) complexes. We found that the sum of coordination bonds' strength, as measured by interaction energies between Be II ion and donor atoms, favours BeNTA but the binding energy of Be II ion to the entire ligand correlates well with experimental trend. Surprisingly, the origin of Be II (NTPA) being more stable is due to less severe repulsive interactions with the backbone of NTPA (C and H-atoms). This general purpose protocol can be employed not only to investigate the origin of relative stability of any molecular system (e.g., metal complexes) but, in principle, can be used as a predictive tool for, e.g., explaining reaction mechanism (transitional states).3

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The physical chemistry of [M(H2O)4(NO3)2] (M = Mn2+, Co2+, Ni2+, Cu2+, Zn2+) complexes: computational studies of their structure, energetics and the topological properties of the electron density

Varadwaj

Marques

2010

Theor Chem Acc

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Low-spin complexes of Ni2+ with six NH3 and H2O ligands: A DFT–RX3LYP study

Cited by 9 publications

References 33 publications

The physical chemistry of coordinated aqua-, ammine-, and mixed-ligand Co2+ complexes: DFT studies on the structure, energetics, and topological properties of the electron density

The physical chemistry of coordinated aqua-, ammine-, and mixed-ligand Co2+ complexes: DFT studies on the structure, energetics, and topological properties of the electron density

Interacting quantum fragments‐rooted preorganized‐interacting fragments attributed relative molecular stability of the Be^IIcomplexes of nitrilotriacetic acid and nitrilotri‐3‐propionic acid

The physical chemistry of [M(H2O)4(NO3)2] (M = Mn2+, Co2+, Ni2+, Cu2+, Zn2+) complexes: computational studies of their structure, energetics and the topological properties of the electron density

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Low-spin complexes of Ni2+ with six NH3 and H2O ligands: A DFT–RX3LYP study

Cited by 9 publications

References 33 publications

The physical chemistry of coordinated aqua-, ammine-, and mixed-ligand Co2+ complexes: DFT studies on the structure, energetics, and topological properties of the electron density

The physical chemistry of coordinated aqua-, ammine-, and mixed-ligand Co2+ complexes: DFT studies on the structure, energetics, and topological properties of the electron density

Interacting quantum fragments‐rooted preorganized‐interacting fragments attributed relative molecular stability of the BeIIcomplexes of nitrilotriacetic acid and nitrilotri‐3‐propionic acid

The physical chemistry of [M(H2O)4(NO3)2] (M = Mn2+, Co2+, Ni2+, Cu2+, Zn2+) complexes: computational studies of their structure, energetics and the topological properties of the electron density

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Interacting quantum fragments‐rooted preorganized‐interacting fragments attributed relative molecular stability of the Be^IIcomplexes of nitrilotriacetic acid and nitrilotri‐3‐propionic acid