title: A step beyond the Feltham-Enemark notation: spectroscopic and correlated ab initio computational support for an antiferromagnetically coupled M(II)-(NO)- description of Tp*M(NO) (M = Co, Ni).
abstract: Multiple spectroscopic and computational methods were used to characterize the ground-state electronic structure of the novel {CoNO}(9) species Tp*Co(NO) (Tp* = hydro-tris(3,5-Me(2)-pyrazolyl)borate). The metric parameters about the metal center and the pre-edge region of the Co K-edge X-ray absorption spectrum were reproduced by density functional theory (DFT), providing a qualitative description of the Co-NO bonding interaction as a Co(II) (S(Co) = 3/2) metal center, antiferromagnetically coupled to a triplet NO(-) anion (S(NO) = 1), an interpretation of the electronic structure that was validated by ab initio multireference methods (CASSCF/MRCI). Electron paramagnetic resonance (EPR) spectroscopy revealed significant g-anisotropy in the S = ½ ground state, but the linear-response DFT performed poorly at calculating the g-values. Instead, CASSCF/MRCI computational studies in conjunction with quasi-degenerate perturbation theory with respect to spin-orbit coupling were required for obtaining accurate modeling of the molecular g-tensor. The computational portion of this work was extended to the diamagnetic Ni analogue of the Co complex, Tp*Ni(NO), which was found to consist of a Ni(II) (S(Ni) = 1) metal center antiferromagnetically coupled to an S(NO) = 1 NO(-). The similarity between the Co and Ni complexes contrasts with the previously studied Cu analogues, for which a Cu(I) bound to NO(0) formulation has been described. This discrepancy will be discussed along with a comparison of the DFT and ab initio computational methods for their ability to predict various spectroscopic and molecular features.
authors: Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany.
authors: Neil C
authors: NC
authors: Tomson
authors: Mark R
authors: MR
authors: Crimmin
authors: Taras
authors: T
authors: Petrenko
authors: Lauren E
authors: LE
authors: Rosebrugh
authors: Stephen
authors: S
authors: Sproules
authors: W Christopher
authors: WC
authors: Boyd
authors: Robert G
authors: RG
authors: Bergman
authors: Serena
authors: S
authors: DeBeer
authors: F Dean
authors: FD
authors: Toste
authors: Karl
authors: K
authors: Wieghardt
mesh_terms: D003035:Cobalt / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008280:Magnetics; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory
chemical_list: D009942:Organometallic Compounds; D009569:Nitric Oxide; D003035:Cobalt; D009532:Nickel; D007501:Iron