The Electronic Spectrum of Re₂Cl₈^2-:  A Theoretical Study

Abstract

One of the prototype compounds for metal−metal multiple bonding, the Re 2 Cl 8 2-ion, has been studied theoretically using multiconfigurational quantum chemical methods. The molecular structure of the ground state has been determined. It is shown that the effective bond order of the Re−Re bond is close to three, due to the weakness of, in particular, the δ bond. The electronic spectrum has been calculated with the inclusion of spin−orbit coupling. Observed spectral features have been reproduced with good accuracy, and a number of new assignments are suggested.

Multiconfiguration Pair-Density Functional Theory: A Fully Translated Gradient Approximation and Its Performance for Transition Metal Dimers and the Spectroscopy of Re2Cl82–

“…The CASSCF calculations yield a significantly multiconfigurational 1 A 1g ground state (the weights of the two most important configurations are 66% and 15%) that has natural orbital occupation numbers of 1.54 and 0.46 in the δ and δ * orbitals, respectively. 57 The lowest-energy excitation is an intra-d-band transition, in particular, a δ to δ * transition ( 1 A 1g to 1 A 2u ). The excited state is also significantly multiconfigurational (the weight of the dominant configuration is 74%); it is an open-shell singlet and is a good test case for MC-PDFT.…”

Assessing Metal–Metal Multiple Bonds in CrCr, MoMo, and WW Compounds and a Hypothetical UU Compound: A Quantum Chemical Study Comparing DFT and Multireference Methods

“…We have previously employed the CASSCF/CASPT2 approach to study several metal-metal multiply bonded species like the [Re 2 Cl 8 ] 2À system, [43] [44] the octabromoditechnetateA C H T U N G T R E N N U N G (III) compound [45] and the triply bonded [Tc 2 X 4 A C H T U N G T R E N N U N G (PMe 3 ) 4 ] (X= Cl, Br) complexes. [46] In all cases the approach has proven to be successful in describing the electronic structure of such compounds and the metal-metal multiple bond, because of its ability to describe the electronic structure of multiconfigurational species.…”

Fully relativistic complete active space self-consistent field for large molecules: Quasi-second-order minimax optimization

“…The rhenium centers in this molecule are d 4 Re(III) ions; we therefore chose our active space to comprise the 4 bonding and 4 anti-bonding 5d orbitals required to describe the formally quadruple bond between the Re ions. [78][79][80][81] Average wall times for the relativistic and non-relativistic calculations are presented in Table I. The difference between the total time per iteration and that spent constructing one-body operators and FCI corresponds to the solution of Eq.…”