Jump to main content
Jump to site search

Issue 5, 2016
Previous Article Next Article

Ammonia-modified Co(II) sites in zeolites: spin and electron density redistribution through the CoII–NO bond

Author affiliations

Abstract

Electronic factors essential for the bonding of a non-innocent NO ligand to ammonia-modified Co2+ sites in cobalt-exchanged zeolites are examined for small cluster models using DFT and advanced correlated wave function calculations. The analysis of charge transfer processes between the NO ligand and the cobalt center involves two protocols: valence-bond expansion of the multiconfiguration CASSCF wave function (in terms of fragment-localized active orbitals) and spin-resolved natural orbitals for chemical valence (SR-NOCV). Applicability of SR-NOCV analysis to transition metal complexes involving non-innocent fragments is critically assessed and the approach based on the CASSCF wave function turns out to be much more robust and systematic for all studied models. It is shown that the character and direction of electron density redistribution through the Co–N–O bond, quantified by relative share of the CoII–NO0, CoIII–NO, and CoI–NO+ resonance structures in the total wave function, fully rationalize the activation of the N–O bond upon NH3 co-ligation (evidenced by calculated and measured red-shift of the NO stretching frequency and commonly ascribed to enhanced backdonation). The huge red-shift of νN–O is attributed to an effective electron transfer between the ammonia-modified Co(II) centers and the NO antibonding π*-orbitals (related to the increased share of the CoIII–NO form). Unexpectedly, the effect is stronger for the singlet complex with three NH3 ligands than for that with five NH3 ligands bound to the cobalt center. Our results also indicate that high-efficiency electron transfers between the Co(II) center and the NO ligand may be enabled for the selected spin state and disabled for the other spin state of the adduct. This illustrates how the cobalt center may serve to fine-tune the electronic communication between the NO ligand and its binding site.

Graphical abstract: Ammonia-modified Co(ii) sites in zeolites: spin and electron density redistribution through the CoII–NO bond

Back to tab navigation

Supplementary files

Publication details

The article was received on 03 Dec 2015, accepted on 05 Jan 2016 and first published on 05 Jan 2016


Article type: Paper
DOI: 10.1039/C5CP07452E
Citation: Phys. Chem. Chem. Phys., 2016,18, 3716-3729
  • Open access: Creative Commons BY-NC license
  •   Request permissions

    Ammonia-modified Co(II) sites in zeolites: spin and electron density redistribution through the CoII–NO bond

    A. Stępniewski, M. Radoń, K. Góra-Marek and E. Broclawik, Phys. Chem. Chem. Phys., 2016, 18, 3716
    DOI: 10.1039/C5CP07452E

    This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. Material from this article can be used in other publications provided that the correct acknowledgement is given with the reproduced material and it is not used for commercial purposes.

    Reproduced material should be attributed as follows:

    • For reproduction of material from NJC:
      [Original citation] - Published by The Royal Society of Chemistry (RSC) on behalf of the Centre National de la Recherche Scientifique (CNRS) and the RSC.
    • For reproduction of material from PCCP:
      [Original citation] - Published by the PCCP Owner Societies.
    • For reproduction of material from PPS:
      [Original citation] - Published by The Royal Society of Chemistry (RSC) on behalf of the European Society for Photobiology, the European Photochemistry Association, and RSC.
    • For reproduction of material from all other RSC journals:
      [Original citation] - Published by The Royal Society of Chemistry.

    Information about reproducing material from RSC articles with different licences is available on our Permission Requests page.

Search articles by author

Spotlight

Advertisements