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Spin‐orbital electronegativity, the X α method, and reactivity at transition‐metal interfaces
Author(s) -
Johnson K. H.
Publication year - 2009
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560120809
Subject(s) - electronegativity , chemistry , molecular orbital theory , molecular orbital , formal charge , non bonding orbital , density functional theory , atomic orbital , orbital overlap , ligand field theory , transition metal , spin polarization , antibonding molecular orbital , metal l edge , chemical physics , computational chemistry , molecular orbital diagram , electron configuration , chemical bond , metal k edge , basis set , electron , linear combination of atomic orbitals , physics , quantum mechanics , molecule , ion , biochemistry , organic chemistry , catalysis
Abstract It is shown that the concept of electronegativity, originally viewed as a virtually constant characteristic of an atom, can be generalized to the individual molecular orbitals of aggregates of atoms, utilizing the self‐consistent field X ‐alpha (SCF‐ X α) density‐functional representation of molecular‐orbital theory in conjunction with the definition of orbital electronegativity proposed by Hinze et al. This generalization allows for the dependence of electronegativity on the detailed electronic structure of a group of atoms as a function of its composition, geometry, and local chemical environment. In transition metals and transition‐metal coordination complexes, where local magnetic spin polarization of electrons is important, the concept of orbital electronegativity can be further generalized to the individual spin‐orbitals. By viewing a transition‐metal surface, cluster, or coordination complex as providing orbital or spin‐orbital pathways for electrons to effectively flow between reactants, where such flow directly between reactants in the gas phase is forbidden by orbital‐symmetry restrictions or unfavorable electronegativity differences, orbital or spin‐orbital electronegativity can be used in conjunction with SCF‐ X α calculations for representative clusters and complexes as an approximate index of heterogeneous or homogeneous reactivity. Recent applications of this concept to a number of problems associated with reactivity at transition‐metal interfaces are reviewed, including: ( 1 ) the dissociation and reactivity of hydrogen at low‐coordination transition‐metal sites, ( 2 ) the interaction of atomic hydrogen with transition‐metal interfaces, and ( 3 ) the surface reactivity of iron.