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

Abstract

Electron descriptors such as bond order and electron density at the bond critical point are key quantities in establishing the characterization of chemical bonding. This paper analyzes a plethora of quantum chemistry data available in the literature to confirm exponential correlations between these electron descriptors and the interatomic distances for any type of chemical bond. This is particularly relevant for extending the crystal chemistry bond order conservation principle to systems with delocalized electrons.

Metal–Metal Bond in the Light of Pauling’s Rules

“…Moreover, Equation (2) is in good agreement with fundamentals of quantum chemistry, namely with exponential decay of the atomic and molecular wavefunctions (or orbitals), and thus may be qualitatively justified (see Ref. [ 13 ] for more details). Nevertheless, it is worth emphasizing that due to the high dispersion of quantum chemistry BOs (see Figure 1 ) obtained by using different recipes and wavefunction qualities, their exponential decay can be clearly established only in a wide range of interatomic distances and only for a sufficiently large variety of the BO data.…”

“…As can be seen, in contrast to the formal BOs, the calculated BOs clearly follow exponential decay, in spite of the high dispersion of the data. A similar analysis of the effective BOs for various atomic pairs obviously confirmed the validity of Equation (2) for both localized and delocalized bonds [ 13 ]. The BV parameters of the TM–TM bonds obtained by fitting the exponential curves allow for a simple but careful calculation of the effective BOs from the TM–TM distances by Equation (2) [ 14 , 15 , 16 ].…”

“…In contrast, the Pauling rules and the BVM were for a long time deemed as inapplicable to compounds with delocalized bonds, e.g., metal cluster compounds (i.e., materials with metal–metal, TM–TM (TM = transition metal), interactions) [ 4 , 7 ]. Only recently, the efficacy of the model for such compounds was shown [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ].…”

Redox Potential and Crystal Chemistry of Hexanuclear Cluster Compounds

“…It was shown that due to the high strains, the difference between effective and formal bond orders may be very high (about 1 v.u.) [ 20 , 34 ]. Nevertheless, due to redistribution of electron density around TMs, the valence (or bond order) deficiency in the metal–metal interactions is commonly compensated for by valence excess in the metal–ligand bonds (bond order conservation principle) [ 23 ].…”

Crystal engineering, crystals and crystallography

“…The 20 or so papers that have been published in IUCrJ in 2018 deal with a wide variety of frontier topics and, for representative purposes only, one might mention papers that have dealt with novel intermolecular interactions of the weakest sort (Shukla et al, 2018), H/D exchange as a tool to control polymorphism (Falk et al, 2018), the ability of 'soft' interactions to direct crystal packing (Sinnwell et al, 2018), the synthesis of multicomponent crystals with large numbers of constituent molecules (Dandela et al, 2018) and the relationship between crystal chemistry principles and quantum chemistry data (Levi et al, 2018). The 20 crystal engineering papers appear among the 75 or so that have been published in IUCrJ this year, and from a total of the 375 or so that have been published overall since the inception of the journal itself.…”