Premium
The Symmetry‐Broken Formalism Applied to the Electronic Structure of an Iminosemiquinone Copper( II ) Catalyst: A Key to the Qualitative Understanding of Its Reactivity
Author(s) -
Bachler Vinzenz,
Chaudhuri Phalguni,
Wieghardt Karl
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010119)7:2<404::aid-chem404>3.0.co;2-1
Subject(s) - copper , formalism (music) , theoretical physics , electronic structure , catalysis , materials science , physics , chemical physics , chemistry , condensed matter physics , metallurgy , organic chemistry , literature , art , musical
A concise outline of the known derivation of the singlet–triplet energy‐gap equations within the symmetry‐broken wavefunction framework is given. They allow a computation of the singlet–triplet energy gap for molecules that exhibit a weak antiferromagnetic coupling of electrons. The accuracy of the equations is assessed by computation of the singlet–triplet gaps in model Na 2 molecules. Various antiferromagnetic coupling strengths are simulated by the use of different Na−Na bond lengths in the computations. The singlet–triplet energy gaps obtained with the different equations are compared with the gaps computed with the more accurate coupled‐cluster methods. Subsequently, the equations are applied to an iminosemiquinone copper( II ) complex found previously to have remarkable catalytic properties. The application is performed by employing wavefunction equations but with quantities computed within the density functional framework. The electronic ground state of this complex is computed to be a singlet state, which is also the experimental finding. Moreover, the experimental geometry and the singlet–triplet gap are reasonably reproduced by the computation. A straightforward method to determine the magnetic orbitals is suggested and applied. We illustrate that the form of the magnetic orbitals indicates in a qualitative manner that hydrogen‐atom abstraction should be a major reaction pathway of the iminosemiquinone copper( II ) complex. Hydrogen‐atom abstraction has been suggested previously to be the rate‐determining step in a catalytic process initiated by the iminosemiquinone copper( II ) complex. The results support the notion that the form of the magnetic orbitals might be a qualitative indicator for the reactivity of molecules that exhibit weak antiferromagnetic coupling.