Do the basic crystal chemistry principles agree with a plethora of recent quantum chemistry data?

The main descriptors of chemical bonding such as bond order (BO) and electron density at the bond critical point, ρ(c), are customarily used to understand the crystal and electronic structure of materials, as well as to predict their reactivity and stability. They can be obtained in the framework of crystal chemistry and quantum chemistry approaches, which are mostly applied as alternatives to each other. This paper verifies the convergence of the two approaches by analyzing a plethora of quantum chemistry data available in the literature. The exponential correlation between the electron descriptors [BO(ij) and ρ(c(ij))] and the length of chemical bonds, R(ij), which is basic in crystal chemistry, was confirmed for 72 atom pairs, regardless of the nature of their interactions (ionic/covalent, metal–metal, etc.). The difference between the BO(ij) (R(ij)) correlations obtained in this work and those accepted in crystal chemistry for the same atomic pairs does not exceed the dispersion of quantum chemistry data, confirming the qualitative validity of the BO conservation principle. Various examples are presented to show that knowledge of the exponential parameters ensures a surprisingly simple determination of two basic electron descriptors in any complex compound with known interatomic distances. In particular, the BO analysis for 20 Re(6)-cluster complexes illustrates the BO conservation for systems with delocalized electrons. Despite the significant transfer of electron density from the Re–Re to the Re–ligand bonds, the total number of Re valence electrons used in bonding remains close to the formal value of seven electrons.