Downloaded from orbit.dtu.dk on: Sep 25, 2021 The Chemical Bond between Transition Metals and Oxygen: Electronegativity, d-Orbital Effects, and Oxophilicity as Descriptors of Metal–Oxygen Interactions Moltved, Klaus A.; Kepp, Kasper Planeta Published in: Journal of Physical Chemistry C Link to article, DOI: 10.1021/acs.jpcc.9b04317 Publication date: 2019 Document Version Peer reviewed version Link back to DTU Orbit Citation (APA): Moltved, K. A., & Kepp, K. P. (2019). The Chemical Bond between Transition Metals and Oxygen: Electronegativity, d-Orbital Effects, and Oxophilicity as Descriptors of Metal–Oxygen Interactions. Journal of Physical Chemistry C, 123(30), 18432-18444. https://doi.org/10.1021/acs.jpcc.9b04317 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Subscriber access provided by DTU Library C: Surfaces, Interfaces, Porous Materials, and Catalysis The Chemical Bond between Transition Metals and Oxygen: Electronegativity, d-Orbital Effects, and Oxophilicity as Descriptors of Metal-Oxygen Interactions Klaus August Moltved, and Kasper P. Kepp J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b04317 • Publication Date (Web): 08 Jul 2019 Downloaded from pubs.acs.org on July 14, 2019 Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. 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ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts. is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties. Page 1 of 40 The Journal of Physical Chemistry 1 2 The Chemical Bond between Transition Metals and Oxygen: Electronegativity, d-Orbital 3 4 Effects, and Oxophilicity as Descriptors of Metal-Oxygen Interactions 5 6 7 Klaus A. Moltved and Kasper P. Kepp* 8 9 10 11 12 13 Technical University of Denmark, DTU Chemistry, Building 206, 2800 Kgs. Lyngby, DK – 14 15 16 Denmark. 17 18 19 20 21 * Corresponding author: Phone: +045 45 25 24 09. E-mail: [email protected] 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 2 of 40 1 2 Abstract. The chemical bonds between a transition metal (M) and oxygen (O) are of major 3 4 importance in catalysis, mineralogy, biology and astrophysics, and adequate theoretical 5 6 7 description of these bonds is thus highly needed. This paper establishes that, despite recent debate 8 9 on its accuracy for transition metal systems, CCSD(T) is an excellent benchmark standard for 10 11 transition metal oxide interactions, with errors approaching those of experiment. We conclude this 12 13 + 14 from a study of all 60 M-O and M -O BDEs of the 3d, 4d, and 5d metals, constituting a balanced 15 16 dataset in terms of dq configurations that also enable an assessment of the trend chemistry in 17 18 oxygen’s ability to bind to transition metals. The BDEs decrease towards the right of the transition 19 20 metal series, with humps at groups 4-5 and 8-9. The linear trend follows the increasing 21 22 23 electronegativity when going from the left to the right, whereas the humps are caused by 24 25 differential occupation of bonding δ-orbitals and antibonding π-orbitals. We show that the BDEs 26 27 correlate strongly with oxophilicity and energies of metal surface chemisorption (R2 = 0.81−0.89), 28 29 30 i.e. the local M-O bond dominates the energetics of transition metals reacting with oxygen. 31 32 Therefore, theoretical studies of oxygen-involving transition metal chemistry should emphasize 33 34 the accuracy of the local M-O bonds. A “bottom-up” approach to theoretical catalysis may thus 35 36 37 produce more accurate trend predictions of relevance to e.g. catalyst design. Finally, our analysis 38 39 explains the large differences in chemisorption of oxygen on metal surfaces as primarily caused 40 41 by the metal electronegativity relative to oxygen, defining the strength of the polar covalent 42 43 bonding, and secondarily to d-orbital net bonding. 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 2 60 ACS Paragon Plus Environment Page 3 of 40 The Journal of Physical Chemistry 1 2 Introduction 3 4 5 The chemical bond between a transition metal and oxygen (M-O) plays a central role in many 6 7 important chemical processes, e.g. catalytic water splitting and conversion of methane to methanol, 8 9 1–4 10 and many catalytic processes involving oxygen reduction. In the mineral world, the main ores 11 12 of a large number of metals are in the form of oxides held together by M-O bonds, and metal 13 14 oxides have very many useful technological applications.5–8 In biology, many enzymes utilize the 15 16 bonding of oxygen to transition metals such as copper or iron to activate the O-O bond for further 17 18 9–11 19 reactions. The simple diatomic M-O systems are very important in astrochemistry, high- 20 21 temperature inorganic chemistry and in order to understand transition metal spectroscopy and 22 23 bonding more fundamentally.12 In particularly, the intense current interest in increasingly small 24 25 26 catalyst systems, with highly effective single-atom catalysts as the ultimate limit, puts a renewed 27 28 focus on understanding single-metal atom ligand interactions as the minimal catalytic unit13,14. 29 30 31 The M-O bond in its pure form describes the tendency of a metal to bind to oxygen, without 32 33 any modulating effects of other metals or ligands. Understanding the intrinsic tendency of metals 34 35 36 to associate with oxygen is an important starting point for understanding the role of the metal in 37 38 many reactions, as presented mainly by the metal’s oxophilicity.15 The fact that this simple, generic 39 40 tendency explains both ore composition and chemical reactions of much more complicated 41 42 systems15 indicates that the local M-O bond dominates the energetics and thus trend chemistry of 43 44 45 real systems relative to the modulating atoms. Many studies use approximate density functional 46 47 methods to study catalysis on metal surfaces.16,17 These studies tacitly assume that the modulating 48 49 catalyst effects are more important to describe with a low-accuracy methods than it is to describe 50 51 52 the directly involved chemical bonds at high accuracy, and thus some accuracy in the M-O bonds 53 54 (and other bonds) is sacrificed to study a larger catalytic system. It is of both fundamental and 55 56 practical interest to understand the relative importance to the trend chemistry of the local M-O 57 58 59 3 60 ACS Paragon Plus Environment The Journal of Physical Chemistry Page 4 of 40 1 2 bond and the modulating effects of the remaining catalyst. Furthermore, the main features that 3 4 drive trends in M-O bonding, i.e. electronegativity vs. d-orbital effects, need to be quantified. 5 6 7 To understand the electronic structure of the M-O bond in detail, we studied in 8 9 + 10 completeness all the 30 neutral MO molecules and the 30 cationic MO systems of the 3d, 4d, and 11 12 5d transition series that define the intrinsic bonding of d-transition metals to oxygen and for which 13 14 experimental bond dissociation enthalpies (BDEs) are available in most cases.18 The 60 diatomic 15 16 systems constitute a balanced data set that allows us to assess the M-O bonding systematically 17 18 19 across all electronic configurations of the 3d, 4d, and 5d transition series.