Relationship Between Structural Characteristics And Constituent Chemical Bonds

On the basis of the concept of chemical bonding, the bond valence model is a valuablemethod to establish the relationship of bond length-bond valence, which provides acorrelation between the crystal and the electronic structures with the characteristic of thesuccinctness, credibility and usefulness. This model attracts attention to interpret and predictcrystal bonding, ion coordination, bond valence distribution and crystal lattice distortion etc.From the viewpoint of the developing history and practical applications of the chemicalbond theory, the chemical bonding characteristics of lanthanide (Ln) complexes, the structuralstability and formability of ABO₃-type perovskite compounds and the octahedral distortion ofd⁰ transition metal cation were systemically studied by using this model in the present work.The current results show that the linear correlations among the mean bond valenceparameters have been well established by a set of linear equations, which provides us a usefulmethod to determine the bond valence parameters in coordination chemistry. A number ofnew Ln-N bond valence parameters were quantitatively estimated which allows us to obtainall Ln-N bond lengths with different coordination numbers and analyze the sum of bondvalence. The new bond valence parameters are more reliable and the bonding ability of Natoms to Ln becomes stronger with Ln contraction phenomenon.A new necessary condition of the structural stability of ABO₃-type perovskitecompounds was established in the range of 0.822-1.139 by calculating bond valence basedtolerance factors. Three new two-dimensional structural maps based on the ideal bonddistances were constructed. The sample points of forming perovskite are distributed indistinctive regions.The average distortion of d⁰ transition metal cations follows the sequence Mo⁶⁺＞V⁵⁺＞＞W⁶⁺＞Nb⁵⁺＞Ti⁴⁺＞＞Ta⁵⁺＞Hf⁴⁺＞Zr⁴⁺, along which these d⁰ cations can be classified intothree types: strong (Mo⁶⁺ and V⁵⁺), moderate (W⁶⁺, Nb⁵⁺ and Ti⁴⁺) and weak (Ta⁵⁺, Hf⁴⁺ andZr⁴⁺). The octahedral distortion of d⁰ transition metal cation increases with increasing itscationic electronegativity. The distortion theorem was proved by the linear correlationbetween the mean bond length and the mean-square deviation of individual bond length.