Nicht in jedem Punkt schuldig: Der “nicht‐unschuldige” Nitrosyl‐Ligand in IUPACs Oxidationsstufen‐Empfehlung

Abstract

Die Bindung eines Nitrosyl‐Liganden an ein Zentralmetallatom wird durch die Wechselwirkung zwischen den beiden N−O‐π*‐ und zwei Metall‐d‐Orbitalen bestimmt. Diese beiden (Rück‐)Bindungen sind weitgehend kovalent, wodurch deren Zuordnung bei der Oxidationsstufenbestimmung erschwert ist. Dabei erweist sich IUPACs “ionische Näherung” als wirksames Werkzeug, um auf der Grundlage der beteiligten Orbitale eine schlüssige Zuordnung zu erreichen – und zwar ohne den M‐N‐O‐Winkel oder Nettoladungen heranzuziehen.

Chasing the Mond Cation: Synthesis and Characterization of the Homoleptic Nickel Tetracarbonyl Cation and its Tricarbonyl‐Nitrosyl Analogue

“…The assignment of oxidation states in nitrosyl complexes is not trivial due the covalent character of the metal nitrosyl bond as published by Klüfers et al [41] . With CASSCF calculations and the effective‐oxidation‐state method [42] they assigned the π‐bonding M‐NO electrons.…”

“…With CASSCF calculations and the effective‐oxidation‐state method [42] they assigned the π‐bonding M‐NO electrons. Yet, due to the covalency of the M‐NO back bonds, small changes in the charge distribution are sufficient to either assign both degenerate π‐MOs to the metal, resulting in a formal NO + ligand, or to allocate all four electrons to the ligand, resulting in a formal NO 3− [41] . Furthermore, complex 1 could be described as Ni II ( S =1) antiferromagnetically coupled to a NO − ( S =1) [43] .…”

Unveiling the atomistic and electronic structure of NiII–NO adduct in a MOF-based catalyst by EPR spectroscopy and quantum chemical modelling

“…Indeed, the open-shell 3d 8 configuration of Ni II , along with the ''noninnocent'' NO ligand, generates a multiconfigurational character in the Ni II -NO electronic structure, extensively observed in the case of the nitrosyl ligands. 14,88,[95][96][97][98][99] Therefore, CASSCF calculations have been employed adopting an active space composed of 11 electrons and 11 orbitals (11e,11o), which involves all the 3d Ni orbitals, the NO p* orbitals, the s-bonding orbitals describing the covalent bonding with the framework of the Ni-MFU-4l-NO 2 and the nitrite ligand and three 4d Ni orbitals.…”

In celebration of the 70thbirthday of Peter Klüfers

“…In a follow up work last year he questions a statement made by IUPAC and found in many textbooks that the geometry of the M(NO) segment can be used to to assign oxidations states of such ligands. [2] Next to the correct description of the bonding conditions in such complexes, the photoinduced linkage isomerism (PLI) was another area of research, which Peter successfully followed over the years.…”