Revealing the nature of electron correlation in transition metal complexes with symmetry breaking and chemical intuition

Abstract

The present work provides a useful framework through which theoreticians and practicing computational chemists alike can view electron correlations in transition metal complexes. We present static correlation from the perspective of simple chemical models such as ligand-field and molecular orbital theories, and an analysis of symmetry breaking suggests that it is rarely encountered in thermochemical calculations of realistic transition metal compounds (though we do reveal a few important situations in which it is relevant). The relative complexity of transition metal bonding, relative to that of typical organic compounds, places a larger burden on a theory's treatment of dynamic correlation. After recognizing that simultaneous sigma-donation and pi-backbonding can be viewed as a correlated interaction involving multiple electron pairs, we demonstrate that MP2 and related double hybrid density functionals fail to describe this type of bonding. File list (2) download file view on ChemRxiv Correlation_in_Metal_Complexes_MS.pdf (773.44 KiB) download file view on ChemRxiv Correlation_in_Metal_Complexes_SI.pdf (123.19 KiB)

Regularized Second-Order Møller–Plesset Theory: A More Accurate Alternative to Conventional MP2 for Noncovalent Interactions and Transition Metal Thermochemistry for the Same Computational Cost

“…17−19 Fortunately, strongly correlated problems 20 are not very common in main group chemistry, or even in transition metal chemistry. 19 However, when strong correlation occurs in the ground state, it typically requires substantially more sophisticated multireference approaches. 21−25 A second well-known class of failures for MP2 theory are problems where the HF orbitals exhibit artificial symmetrybreaking even though there are no obvious strong correlations.…”

“…MP2 theory typically overestimates the strength of such binding, which again suggests that important nonadditive electron correlation effects are at play. 19 As for collective dispersion interactions, this information has been used to argue for the necessity of using infinite order methods.…”

“…The TM systems investigated in this work do not display static correlation, as supported by the absence of spin-symmetry breaking at the UHF level. 19 All molecules in the MOR39 set are closed-shell singlets, and the systems in the MCO9 set have relatively large gaps (compared to other metal complexes) because the carbonyl ligands are strong-field. Indeed, the MOR39 molecules have an average HOMO−LUMO gap of 10.6 kcal/mol.…”

Synthesis, anti‐proliferative activities, docking studies, and computational calculations of novel isonicotinic mixed complexes

“…On the other hand, the charge transfer resistance ( R ct ) decreases for Cd( II ) > Cu( II ) > Co( II ) > Cr( III ) > Fe( III ) complexes to be 37.05, 35.5, 27.6, 26.9, and 20.6 Ω, respectively, which indicate that Cd( II ) complexes have the lowest electroactive properties and the Cr( III ) and Fe( III ) complexes have the highest electroactive properties. [ 53 ]…”

“…As a result, the modified electrode surfaces with the targeted complexes showed higher Faradaic current that produces from the existence of a thin film of the complex at the electrode surface. The obtained results are visualized in Figure 12a,b, and the intensive summary is sorted in [53] The direct oxidation-reduction of the original complexes was further investigated without the use of redox mediators to show whether the complex itself could provide redox readouts. Thus, in the KCl solution, the electrodes were tested and the results are presented in Figure 13a-e.…”