Generalized Stress-Redox Equivalence: A Chemical Link between Pressure and Electronegativity in Inorganic Crystals

Abstract

The crystal structure of many inorganic compounds can be understood as a metallic matrix playing the role of a host lattice in which the nonmetallic atomic constituents are located, the Anions in Metallic Matrices (AMM) model stated. The power and utility of this model lie in its capacity to anticipate the actual positions of the guest atoms in inorganic crystals using only the information known from the metal lattice structure. As a pertinent test-bed for the AMM model, we choose a set of common metallic phases along with other nonconventional or more complex structures (face-centered cubic (fcc) and simple cubic Ca, CsCl-type BaSn, hP4-K, and fcc-Na) and perform density functional theory electronic structure calculations. Our topological analysis of the chemical pressure (CP) scalar field, easily derived from these standard first-principles electronic computations, reveals that CP minima appear just at the precise positions of the nonmetallic elements in typical inorganic crystals presenting the above metallic subarrays: CaF 2 , rock-salt, and CsCl-type phases of CaX (X = O, S, Se, Te), BaSnO 3 , K 2 S, and NaX (X = F, Cl, Br, I). A theoretical basis for this correlation is provided by exploring the equivalence between hydrostatic pressure and the oxidation (or reduction) effect induced by the nonmetallic element on the metal structure. Indeed, our CP analysis leads us to propose a generalized stress-redox equivalence that is able to account for the two main observed phenomena in solid inorganic compounds upon crystal formation: (i) the expansion or contraction experienced by the metal structure after hosting the nonmetallic element while its topology is maintained and (ii) the increasing or decreasing of the effective charge associated with the anions in inorganic compounds with respect to the charge already present in the interstices of the metal network. We demonstrate that a rational explanation of this rich behavior is provided by means of Pearson-Parr's electronegativity equalization principle. INTRODUCTIONThe literature on the theories and formalisms describing chemical bonding in inorganic crystal structures is very extensive, 1−6 and the models can typically be classified into either classical or quantum types. Among them, the approach of Pauling has been the paradigm for describing and rationalizing the crystal structures of ionic compounds over the last century. 7,8 The limitations of the ionic model, which have also led to a number of misconceptions about the crystal structure and the bonding network, were discussed by O'Keeffe and Hyde using alternative approaches. 9,10 These authors put the emphasis on the description of the structures of oxides as oxygen-stuffed alloys, since their cationic sublattices adopt the structures of either elements or simple alloys. Interestingly, this concept can also be applied to the naked metallic structure if the valence electrons localized in the empty spaces of the structure are conceived as coreless 49 pseudoanions. In fact, the term electride was introduced af...

Comment on “Uncommon structural and bonding properties in Ag16B4O10” by A. Kovalevskiy, C. Yin, J. Nuss, U. Wedig, and M. Jansen, Chem. Sci., 2020, 11, 962

“…The relevant eight ELF attractors still appear at the tetrahedral positions. However, and in concordance with the generalized stress-redox correlation, 15 the electron population inside the basins of the tetrahedral voids decreases at this expanded sub-lattice. This is a consequence of the lower overlap between the electron density clouds of neighbouring atoms when their internuclear distance increases.…”

Relating atomic energy, radius and electronegativity through compression

“…Detailed analyses and consideration of electronic structure will always be necessary for quantitative evaluations of, e.g., bond strength and polarity. 66,67…”

Highs and Lows of Bond Lengths: Is There Any Limit?

“…In the same way, when the molecule is compressed up to the limit where the electronic repulsion dominates, the bonding electrons suffer a strong confinement in a really tiny space, the cores began to repel with each other and, formally, the bond disappear forming an inner valence shells interaction. The activation of the core electrons at the hard sphere point would have a deep impact in the ionization potential or in the electronegativity of the atoms, as previously noticed in the high‐pressure field [44–47] …”

“…The activation of the core electrons at the hard sphere point would have a deep impact in the ionization potential or in the electronegativity of the atoms, as previously noticed in the high‐pressure field. [ 44 , 45 , 46 , 47 ]…”