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Leach IF, Klein JEMN. Oxidation States: Intrinsically Ambiguous? ACS CENTRAL SCIENCE 2024; 10:1406-1414. [PMID: 39071055 PMCID: PMC11273457 DOI: 10.1021/acscentsci.4c00825] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/23/2024] [Revised: 06/10/2024] [Accepted: 06/10/2024] [Indexed: 07/30/2024]
Abstract
The oxidation state ( OS ) formalism is a much-appreciated good in chemistry, receiving wide application. However, like all formalisms, limitations are inescapable, some of which have been recently explored. Providing a broader context, we discuss the OS and its interpretation from a computational perspective for transition metal (TM) complexes. We define a broadly applicable and easy-to-use procedure to derive OS s based on quantum chemical calculations, via the use of localized orbitals, dubbed the Intrinsic OS . Applying this approach to a cobalt complex in five OS s, isolated by Hunter and co-workers (Inorg. Chem.2021, 60, 17445), we find that the calculated Intrinsic OS matches the formal OS , consistent with the experimental characterization. Through analysis of the delocalized orbitals, the ligand field of the Co(III) complex is found to be "inverted", despite every cobalt-ligand bond being classically dative from the localized perspective-a bonding scenario very similar to that of [Cu(CF3)4]-. This is not atypical but rather a natural consequence of these metals bonding in the high-valent region, and we propose a more restrictive definition of (locally) inverted bonding. Additionally, two bonding descriptors within the Intrinsic Bonding Orbital (IBO) framework (σ-gain and π-loss) are introduced, which enable facile quantification of electron-sharing covalency across a broad range of TM complexes.
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Affiliation(s)
- Isaac F. Leach
- Molecular
Inorganic Chemistry, Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 3, 9747
AG Groningen, The
Netherlands
- Zernike
Institute for Advanced Materials, University
of Groningen, Nijenborgh
3, 9747 AG Groningen, The Netherlands
| | - Johannes E. M. N. Klein
- Molecular
Inorganic Chemistry, Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 3, 9747
AG Groningen, The
Netherlands
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Winter MJ. Chemdex: quantification and distributions of valence numbers, oxidation numbers, coordination numbers, electron numbers, and covalent bond classes for the elements. Dalton Trans 2024; 53:493-511. [PMID: 38087991 DOI: 10.1039/d3dt03738j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2024]
Abstract
The paper introduces Chemdex, a freely accessible web-based database of over 70 000 compounds characterised by crystallography from across the periodic table. Its software calculates for an atom of interest within each compound classifications including valence number, oxidation number, coordination number, electron number, several covalent bond classifications, and the attached atom set. Users may explore distributions of these classifications by percentages and heat map displays for individual elements or sets of elements, or in several cases for one classification plotted against a second. These properties often display clear periodicity. Based upon distributions across the periodic table of valence numbers, electron numbers, coordination numbers, and attached atom data suggestions are made regarding the placement of hydrogen in the periodic table, membership of group 3 in the periodic table, locations of the early actinoids in the periodic table, and assignments of certain elements as metalloids.
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Affiliation(s)
- Mark J Winter
- Department of Chemistry, The University of Sheffield, Sheffield S3 7HF, UK.
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Phung QM, Nam HN, Ghosh A. Local Oxidation States in {FeNO} 6-8 Porphyrins: Insights from DMRG/CASSCF-CASPT2 Calculations. Inorg Chem 2023. [PMID: 38010736 DOI: 10.1021/acs.inorgchem.3c03689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
A first DMRG/CASSCF-CASPT2 study of a series of paradigmatic {FeNO}6, {FeNO}7, and {FeNO}8 heme-nitrosyl complexes has led to substantial new insight as well as uncovered key shortcomings of the DFT approach. By virtue of its balanced treatment of static and dynamic correlation, the calculations have provided some of the most authoritative information available to date on the energetics of low- versus high-spin states of different classes of heme-nitrosyl complexes. Thus, the calculations indicate low doublet-quartet gaps of 1-4 kcal/mol for {FeNO}7 complexes and high singlet-triplet gaps of ≳20 kcal/mol for both {FeNO}6 and {FeNO}8 complexes. In contrast, DFT calculations yield widely divergent spin state gaps as a function of the exchange-correlation functional. DMRG-CASSCF calculations also help calibrate DFT spin densities for {FeNO}7 complexes, pointing to those obtained from classic pure functionals as the most accurate. The general picture appears to be that nearly all the spin density of Fe[P](NO) is localized on the Fe, while the axial ligand imidazole (ImH) in Fe[P](NO)(ImH) pushes a part of the spin density onto the NO moiety. An analysis of the DMRG-CASSCF wave function in terms of localized orbitals and of the resulting configuration state functions in terms of resonance forms with varying NO(π*) occupancies has allowed us to address the longstanding question of local oxidation states in heme-nitrosyl complexes. The analysis indicates NO(neutral) resonance forms [i.e., Fe(II)-NO0 and Fe(III)-NO0] as the major contributors to both {FeNO}6 and {FeNO}7 complexes. This finding is at variance with the common formulation of {FeNO}6 hemes as Fe(II)-NO+ species but is consonant with an Fe L-edge XAS analysis by Solomon and co-workers. For the {FeNO}8 complex {Fe[P](NO)}-, our analysis suggests a resonance hybrid description: Fe(I)-NO0 ↔ Fe(II)-NO-, in agreement with earlier DFT studies. Vibrational analyses of the compounds studied indicate an imperfect but fair correlation between the NO stretching frequency and NO(π*) occupancy, highlighting the usefulness of vibrational data as a preliminary indicator of the NO oxidation state.
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Affiliation(s)
- Quan Manh Phung
- Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
| | - Ho Ngoc Nam
- Institute of Materials Innovation, Institutes of Innovation for Future Society, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
- Department of Chemical Systems Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603, Japan
| | - Abhik Ghosh
- Department of Chemistry, UiT the Arctic University of Norway, N-9037 Tromsø, Norway
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Hypervalence: A Useful Concept or One That Should Be Gracefully Retired? CHEMISTRY 2022. [DOI: 10.3390/chemistry4040082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In this essay the origins of the term hypervalence and its application in p-block element chemistry are considered and it is argued that the term should now be consigned to the graveyard of concepts that no longer afford any discernible value or insight, certainly from an educational perspective. In contrast, the educational merits of the octet rule are also examined where it is concluded that this rule does have significant pedagogical value, albeit mostly within the ambit of introductory level explanations. For a few of the chosen exemplar compounds, a selection of orbital-based analyses, at different levels of sophistication, are also considered, and their values appraised together with a brief survey of some of the more general computational studies which have been employed in relation to this topic.
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Wheaton AM, Chipman JA, Roy MD, Berry JF. Metal-Metal Bond Umpolung in Heterometallic Extended Metal Atom Chains. Inorg Chem 2022; 61:15058-15069. [PMID: 36094078 PMCID: PMC9632685 DOI: 10.1021/acs.inorgchem.2c02118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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Understanding the fundamental properties governing metal–metal
interactions is crucial to understanding the electronic structure
and thereby applications of multimetallic systems in catalysis, material
science, and magnetism. One such property that is relatively underexplored
within multimetallic systems is metal–metal bond polarity,
parameterized by the electronegativities (χ) of the metal atoms
involved in the bond. In heterobimetallic systems, metal–metal
bond polarity is a function of the donor–acceptor (Δχ)
interactions of the two bonded metal atoms, with electropositive early
transition metals acting as electron acceptors and electronegative
late transition metals acting as electron donors. We show in this
work, through the preparation and systematic study of a series of
Mo2M(dpa)4(OTf)2 (M = Cr, Mn, Fe,
Co, and Ni; dpa = 2,2′-dipyridylamide; OTf = trifluoromethanesulfonate)
heterometallic extended metal atom chain (HEMAC) complexes that this
expected trend in χ can be reversed. Physical characterization
via single-crystal X-ray diffraction, magnetometry, and spectroscopic
methods as well as electronic structure calculations supports the
presence of a σ symmetry 3c/3e– bond that
is delocalized across the entire metal-atom chain and forms the basis
of the heterometallic Mo2–M interaction. The delocalized
3c/3e– interaction is discussed within the context
of the analogous 3c/3e– π bonding in the vinoxy
radical, CH2CHO. The vinoxy comparison establishes three
predictions for the σ symmetry 3c/3e– bond
in HEMACS: (1) an umpolung effect that causes the
Mo–M interactions to become more covalent as Δχ
increases, (2) distortion of the σ bonding and non-bonding orbitals
to emphasize Mo–M bonding and de-emphasize Mo–Mo bonding,
and (3) an increase in Mo spin population with increasing Mo–M
covalency. In agreement with these predictions, we find that the Mo2···M covalency increases with increasing Δχ
of the Mo and M atoms (ΔχMo–M increases
as M = Cr < Mn < Fe < Co < Ni), an umpolung of the trend predicted in the absence of σ delocalization.
We attribute the observed trend in covalency to the decreased energic
differential (ΔE) between the heterometal orbital and the σ bonding molecular
orbital of the Mo2 quadruple bond, which serves as an energetically
stable, “ligand”-like electron-pair donor to the heterometal
ion acceptor. As M is changed from Cr to Ni, the σ bonding and
nonbonding orbitals do indeed distort as anticipated, and the spin
population of the outer Mo group is increased by at least a factor
of 2. These findings provide a predictive framework for multimetallic
compounds and advance the current understanding of the electronic
structures of molecular heteromultimetallic systems, which can be
extrapolated to applications in the context of mixed-metal surface
catalysis and multimetallic proteins. This
work describes how use of a metal−metal quadruply
bonded metalloligand can reverse expected trends in metal−metal
bond polarity through the preparation and systematic study of a novel
series of Mo2M(dpa)4(OTf)2 (M = Cr,
Mn, Fe, Co, and Ni) heterotrimetallic extended metal atom chain (HEMAC)
complexes. These complexes feature a 3c/3e− metal−metal
bond that is delocalized across the entire metal atom chain and is
compared to the 3c/3e− π bonding in the vinoxyl
radical.
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Affiliation(s)
- Amelia M Wheaton
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Jill A Chipman
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Michael D Roy
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - John F Berry
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
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Green JC. Comment on "In Defence of Oxidation States" by N. C. Norman and P. G. Pringle, Dalton Transactions, 2022, 51, DOI: 10.1039/D0DT03914D. Dalton Trans 2021; 51:746-747. [PMID: 34931634 DOI: 10.1039/d1dt02930d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The evolution of the Covalent Bond Classification as a pedagogical tool for classifying an element's chemistry is described.
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Affiliation(s)
- Jennifer C Green
- Department of Chemistry, Inorganic Chemistry laboratory, South Parks Road, Oxford OX1 3QR, UK.
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Norman NC, Pringle PG. Reply to the 'Comment on "In Defence of Oxidation States"' by J. C. Green, Dalton Transactions, 2022, 51, DOI: 10.1039/D1DT02930D. Dalton Trans 2021; 51:748-749. [PMID: 34931641 DOI: 10.1039/d1dt03725k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We reiterate and reinforce some of the points concerning oxidation states and the Covalent Bond Classification method we made in the Perspective article entitled 'In Defence of Oxidation States' including a brief discussion of the relative merits of the terms 'metathesis' and 'redox' when considering addition across a metal-metal bond.
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Affiliation(s)
| | - Paul G Pringle
- University of Bristol, School of Chemistry, Bristol, BS8 1TS, UK.
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