title: Singlet-Triplet Gaps of Cobalt Nitrosyls: Insights from Tropocoronand Complexes.
abstract: A density functional theory (DFT) study of {CoNO}(8) cobalt nitrosyl complexes containing the [n,n]tropocoronand ligand (TC-n,n) has revealed a sharp reduction of singlet-triplet gaps as the structures change from near-square-pyramidal (for n = 3) to trigonal-bipyramidal with an equatorial NO (for n = 5, 6). An experimental reinvestigation of [Co(TC-3,3)(NO)] has confirmed that it is not paramagnetic, as originally reported, but diamagnetic, like all other {CoNO}(8) complexes. Furthermore, DFT calculations indicate a substantial singlet-triplet gap of about half an eV or higher for this complex. At the other end of the series, low-energy, thermally accessible triplet states are predicted for [Co(TC-6,6)(NO)]. Enhanced triplet-state reactivity may well provide a partial explanation for the failure to isolate this compound as a stable species.
authors.affiliation: †Department of Chemistry and Center for Theoretical and Computational Chemistry, University of Tromsø, N-9037 Tromsø, Norway.
authors.forename: Kathrin H
authors.initials: KH
authors.lastname: Hopmann
authors.affiliation: †Department of Chemistry and Center for Theoretical and Computational Chemistry, University of Tromsø, N-9037 Tromsø, Norway.|‡Department of Chemistry, University of the Free State, 9300 Bloemfontein, Republic of South Africa.
authors.forename: Jeanet
authors.initials: J
authors.lastname: Conradie
authors.affiliation: †Department of Chemistry and Center for Theoretical and Computational Chemistry, University of Tromsø, N-9037 Tromsø, Norway.
authors.forename: Espen
authors.initials: E
authors.lastname: Tangen
authors.affiliation: ⊥Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, United States.|∥Department of Chemistry, University of Texas at San Antonio, San Antonio, Texas 78249, United States.
authors.forename: Zachary J
authors.initials: ZJ
authors.lastname: Tonzetich
authors.affiliation: ⊥Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, United States.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Lippard
authors.affiliation: †Department of Chemistry and Center for Theoretical and Computational Chemistry, University of Tromsø, N-9037 Tromsø, Norway.
authors.forename: Abhik
authors.initials: A
authors.lastname: Ghosh
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D008024:Ligands; D047028:Macrocyclic Compounds / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009584:Nitrogen / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D008024:Ligands; D047028:Macrocyclic Compounds; D009942:Organometallic Compounds; D003035:Cobalt; D009584:Nitrogen