Restoring orbital thinking from real space descriptions: bonding in classical and non-classical transition metal carbonyls

Abstract

A combined strategy that unifies our interacting quantum atoms approach (IQA), a chemically intuitive energetic perspective within the quantum theory of atoms in molecules (QTAIM), the domain natural orbitals obtained by the diagonalization of the charge-weighted domain-averaged Fermi hole (DAFH), and the statistical analyses of chemical bonding provided by the electron number distribution functions (EDF) is presented. As shown, it allows for recovering traditional orbital images from the orbital invariant descriptions of QTAIM. It does also provide bonding indices (like bond orders) and bond energetics, all in a per orbital basis, still invariant manner, using a single unified framework. The procedure is applied to show how the Dewar, Chatt, and Ducanson model of bonding in simple transition metal carbonyls may be recovered in the real space. The balance between the number of s-donated and p-backdonated electrons is negative in classical compounds and positive in non-classical ones. The energetic strength of backdonation is, however, smaller than that of donation. Our technique surpasses conventional orbital models by providing physically sound, quantitative energetics of chemical bonds (or interactions) together with effective one-electron pictures, all for arbitrary wavefunctions.

An Interacting Quantum Atoms Analysis of the Metal–Metal Bond in [M2(CO)8]n Systems

“…We have recently proposed a method that, combining IQA and DAFH approaches, is able to recover the molecular orbital language from a real space descriptions. 68 However, the computational efforts for a full IQA-DAFH analysis is, at the moment, too expensive. A future parallelization of PROMOLDEN code will allow to increase the size of the systems suitable to be studied with this new approach.…”

“…IQA has been previously used to obtain chemically relevant information and to shed light on many aspects relative to chemical bonding and binding in a wide variety of systems, [40][41][42][43][44][45][46] including different metal-organic compounds. [47][48][49] The purpose of this article is to carry out similar IQA analyses on the MM interaction and bonding of the aforementioned dimetal polycarbonyl dimers.…”

Cooperative and anticooperative effects in resonance assisted hydrogen bonds in merged structures of malondialdehyde

“…More specifically, we employed the Interacting Quantum Atoms (IQA) energy partition as well as the Quantum Theory of Atoms in Molecules (QTAIM) to analyze the interplay between a given RAHB and its surrounding π bonds as well as the resultant HB cooperative or anticooperative effects. We have chosen these methods of wavefunction analyses for this investigation due to its successful use in the study of different non-additive interactions such as those in H-bond within small water clusters [22,23] , back-bonding in transition metal carbonyl complexes [24,25] , or in n → π transitions in electronic excited states [26] . Altogether, our results provide an assessment of the interaction of an RAHB and its neighboring cojugated system on top of HB π cooperative and anticooperative effects.…”

The atomic orbitals of the topological atom

“…Even though their origin is different, the DAFH and "effective AO" analyses share some similarities, particularly when the DAFH analysis is carried out over a single atomic domain. In fact, in the restricted single-determinant case the orbitals before isopycnic localization, sometimes denoted as domain natural orbitals, 33 are exactly the same as the original "effective AOs." 29 The special features of the "effective AOs" in the framework of QTAIM (or any disjoint partition of the space in general) suggests that they could be used as (numerical) atomic basin-centered orthogonal basis set, in which the actual molecular orbitals of the molecule can be expanded.…”

“…It is fair to note that the formalism of the domainaveraged Fermi hole analysis 32,33 (DAFH) also produces orbital functions in the framework of QTAIM (or other AIM schemes). With the DAFH analysis, one first obtains a set of domain orbitals and orbitals occupancies, that have their origin in the average of the exchange-correlation density over a space domain, typically the union of several atomic domains.…”