Abstract
About 70 years ago, in the framework of his theory of chemical bonding, Pauling proposed an empirical correlation between the bond valences (or effective bond orders (BOs)) and the bond lengths. Till now, this simple correlation, basic in the bond valence model (BVM), is widely used in crystal chemistry, but it was considered irrelevant for metal–metal bonds. An extensive analysis of the quantum chemistry data computed in the last years confirms very well the validity of Pauling’s correlation for both localized and delocalized interactions. This paper briefly summarizes advances in the application of the BVM for compounds with TM–TM bonds (TM = transition metal) and provides further convincing examples. In particular, the BVM model allows for very simple but precise calculations of the effective BOs of the TM–TM interactions. Based on the comparison between formal and effective BOs, we can easily describe steric and electrostatic effects. A possible influence of these effects on materials stability is discussed.
Highlights
In 1929, based on the first structural studies, Pauling formulated five simple rules to rationalize chemical bonding in minerals [1]
The bond order (BO) sum, Σ BOij, or the bond valence sum, BVS = Σ sij, around atom i should be equal to its valence, Vi: Σ BOij = Σ sij = Vi
This paper briefly summarizes the advance in the application of the bond valence model (BVM) to compounds with metal–metal bonding, presenting novel examples and focusing on the validity of Pauling’s rules for these materials
Summary
In 1929, based on the first structural studies, Pauling formulated five simple rules to rationalize chemical bonding in minerals [1]. In 1947 Pauling related the BOij to respective interatomic distance, Rij, by empirical constants [2]. This correlation can be written as follows: sij = exp [(R0 ij − Rij)/bij], (2). The constants R0 ij and bij are known as bond valence (BV) parameters, transferable for a given atom pair in different compounds. They represent an effective repulsion between i and j atoms and the softness of the bond, respectively [3,4]
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