The Chemical Bond between Transition Metals and Oxygen: Electronegativity, d-Orbital Effects, and Oxophilicity as Descriptors of Metal–Oxygen Interactions

Abstract

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Chemical Causes of Metal Nobleness

“…The correlation in Figure 2A, as other data (e. g. O 2chemisorption energies correlating with MÀ O diatomic bond energies [53] ), show that the major trends in bulk metal reactivity are driven by the local electronic structure of the individual metal atoms, a fact that may be obscured by the emphasis on delocalized band structure. Tungsten illustrates well the strong relationship, having the highest ΔG at as well as the strongest metal-metal bonds, reflecting the optimally occupied netbonding diffuse 5d-states producing better overlapping 5d-5d bonds with enhanced covalent character.…”

“…[36,52] Specifically, spin-orbit coupling changes MÀ O bond strengths up to 30 kJ / 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 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 mol for some 5d metals (34 kJ/mol for Au + À O) but almost not for Ag and Pd because of the steep dependence on Z. [53] Although typically not mentioned at all, [29,54] this neglect substantially reduces the accuracy of most theoretical Pd/Pt and Ag/Au comparisons, one example being the relative position of Pd and Pt in volcano plots separated by 0.1-0.2 V [54] when neglecting spin-orbit effects up to 0.3 V. [53] Accordingly, when comparing 4d and 5d metals as in the case of noble metals of interest here, the theoretical estimates should be viewed with some caution.…”

“…[53] Unfortunately, the effect depends on electronic configuration and tends to oscillate across the 5d period, making it hard to predict without explicit calculation. [53] The spin-orbit coupling thus becomes important when analyzing the relative reactivity and nobleness of 4d and 5d metals.…”

“…The validity of such a scaling is well established, and thus for simplicity we consider only the surface binding energy of the oxygen atom. [53,69] To evaluate the relative importance of the three processes and their involved energies to the reactivity (and thus nobleness) of the metals, Figure 3B shows a convenient way of mapping the metals of the periodic table, by plotting the sum of the first and second IPs against the free energy of hydration of the M 2 + ions. This plot enables a good distinction between the metal blocks and in particular a metric of the similarity of the metals, with the nobles metals being placed farthest to the lower right, and the most reactive and oxophilic metals being located to the upper left.…”

Dioxygen Binding to all 3d, 4d, and 5d Transition Metals from Coupled‐Cluster Theory

“…Experimental errors in both molecular and surface MÀ O bond energies are perhaps~20 kJ/mol. [45][46][47][48] In comparison, typical oxygen-bonding errors from density functional theory (DFT) are 50 kJ/mol both for surfaces [46] and molecular systems. [47,49] Best performances do not exceed 30 kJ/mol, even for the cleanest and simplest systems where chemical composition and thermodynamic effects are fully controlled.…”