Bond Strength of a Diatomic Acceptor Ligand: A Reliable Measure of Its Antibond Occupation and Its Charge?

Abstract

A nitrosyl ligand is bonded to a central metal mainly via a mostly covalent normal bond and a coordinative metal‐to‐NO π‐backbond. A recent analysis had unravelled similar bonding characteristics of both linear and bent CoNO moieties in terms of ligand charge and antibond occupation. Thus, there should be no justification for the usual assignment of an NO+ ligand to a linear MNO unit and a singlet‐NO− ligand to a bent one. This claim seems to contradict that bending an MNO unit weakens the N−O bond with a marked red‐shift of the N−O stretch as one indicator. In this work, the failure of Dewar‐Chatt‐Duncanson‐derived conclusions is demonstrated for linear/bent isomer couples by the analysis of M−N and N−O bond strengths. Instead of DCD behavior, lateral electrostatic influence on NO and other diatomic ligands modulates the intraligand bond strength in a similar way as has been shown in former work for polar interaction of a charge with CO in the ‘non‐classical’ carbonyls. Methodologically, local‐mode analysis is used to determine bond strengths. Oxidation states are determined by the effective‐oxidation‐state (EOS) method.

Local force constants and charges of the nitrosyl ligand in photoinduced NO linkage isomers in a prototypical ruthenium nitrosyl complex

“…, the two-atomic system NO, which then should be true, independent of the system in which the NO is integrated. This can be clearly seen when inserting the calculated decoupled values from the study of Popp & Kluefers 28 for different metal-nitrosyl complexes, as shown in Fig. 7.…”

“…26 Fundamental insight into these questions and, especially, also with respect to the oxidation state of the ''non-innocent'' ligand NO, has been given in the recent work by Klu ¨fers and co-workers. 27,28 Through detailed structure analysis combined with DFT calculations and the determination of the charges on the NO, it was shown that the M-N-O angle is not a reliable indicator to derive bond strengths or ligand charges.…”

Pas de Deux of an NO Couple: Synchronous Photoswitching from a Double‐Linear to a Double‐Bent Ru(NO)2 Core under Nitrosyl Charge Conservation

“…Hence, the GS/MS transition of 1 is a non‐DCD event which lacks the DCD‐typical charge/bond‐strength correlation of an acceptor ligand. The physical origin of the observed redshift, lateral electrostatic influence on bending, is addressed in a separate work [22] …”

Ein pas de deux eines NO‐Paares: synchrones lichtinduziertes Schalten von einem doppelt‐linearen zu einem doppelt‐gewinkelten Ru(NO)2‐Fragment bei gleich bleibender Nitrosylladung

“…schen Ursache der beobachteten Rotverschiebung, nämlich lateraler elektrostatischer Einfluss bei der Abwinkelung, wird in einer eigenen Arbeit adressiert. [22] Der TS lohnt eine nähere Betrachtung. Entgegen der üblichen Zuordnung der Ladungen in linearen und gewinkelten MNO-Funktionen ändern sich im Verlauf des linear/gewinkelt-Übergangs in 1 die Ladungen der Nitrosylliganden nicht signifikant.…”

“…Es wird deutlich, dass die GS/MS‐Umwandlung in 1 kein DCD‐Ereignis ist und daher der DCD‐typischen Ladungs–Bindungsstärke‐Beziehung die Grundlage fehlt. Die physikalischen Ursache der beobachteten Rotverschiebung, nämlich lateraler elektrostatischer Einfluss bei der Abwinkelung, wird in einer eigenen Arbeit adressiert [22] …”