Stereochemistry of Transition-Metal Dinitrosyl Complexes. A Molecular Orbital Rationale for the Attracto and Repulso Conformations

Abstract

Transition metal dinitrosyl complexes constitute a fairly large class of compounds, exemplified by some 500 structures in the Cambridge Structural Database. While many of the complexes exhibit a claw-like cis-attracto conformation, a handful of them exhibit a peculiar repulso conformation, in which the two NO groups are splayed outward and away from each other. Surprisingly, no computational study to date has attempted to explain the existence of these two limiting conformations of cis-dinitrosyl complexes. Careful examination of the large body of structural data and DFT-based molecular orbital analyses have identified both specific Enemark-Feltham electron counts and metal-ligand orbital interactions as crucial to each of the two conformations. Thus, the common attracto conformation, which is favored by as many as four metal(d)-NO(π*) orbital interactions, is observed most characteristically in four-and fivecoordinate cis-{M(NO) 2 } 8 complexes. The rarer repulso conformation, characterized by an unusually wide NMN´ angle, appears to be typical of pseudotetrahedral {M(NO) 2 } 10 complexes involving 4d and 5d transition metals. These complexes exhibit an a 1-symmetry (under a C 2v molecular point group) metal(d)-NO(π*) orbital interaction that uniquely favors a repulso geometry. This orbital interaction, however, appears to be weaker for 3d orbitals, which are significantly smaller than 4d and 5d orbitals. Pseudotetrahedral {M(NO) 2 } 10 complexes involving a 3d transition metal accordingly thus tend to exhibit an attracto conformation for hard, nitrogenbased supporting ligands but repulso-like/borderline conformations for soft phosphine and thioether-type supporting ligands.

Insight into the Electronic Structure of Biomimetic Dinitrosyliron Complexes (DNICs): Toward the Syntheses of Amido-Bridging Dinuclear DNICs

“…Chart summarizes the structure-characterized mononuclear {Fe­(NO) 2 } 9 /{Fe­(NO) 2 } 10 , dinuclear {Fe­(NO) 2 } 9 -{Fe­(NO) 2 } 9 /{Fe­(NO) 2 } 9 -{Fe­(NO) 2 } 10 /{Fe­(NO) 2 } 10 -{Fe­(NO) 2 } 10 , and tetranuclear [{Fe­(NO) 2 } 9 ] 4 DNICs discussed in this Forum Article. On the basis of the single-crystal X-ray structure of DNICs available in the Cambridge Crystallographic Data Centre (CCDC) database, classical DNICs with different types of supporting ligands and alternative redox levels feature an attracto conformation for the DNIU [Fe­(NO) 2 ] and a tetrahedral geometry for the Fe center [molecular orbital (MO) rationale for the attracto and repulso conformations for transition-metal dinitrosyl complexes was communicated recently] . Spectroscopic discriminations of these different types of DNICs by EPR spectroscopy, infrared (IR) spectroscopy, Fe/S K-edge X-ray absorption near-edge spectroscopy, and 15 N NMR were reviewed elsewhere .…”

“…Spectroscopic and computational insights, moreover, rationalized the synthetic cycles for NO-to-N . 32 Spectroscopic discriminations of these different types of DNICs by EPR spectroscopy, infrared (IR) spectroscopy, Fe/S K-edge X-ray absorption near-edge spectroscopy, and 15 N NMR were reviewed elsewhere. 30 In the following sessions, we will review the spectroscopic and computational insights into the bonding nature within the [Fe(NO) 2 ] unit and the electronic structure of classical DNICs, whereas the study of metallothiolate-bound DNICs is reported in other literature.…”

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

“…In a recent work, Ghosh and Conradie classified dinitrosyl structures in terms of electronic and geometrical parameters. [14] 1 follows their rules for an {M(NO) 2 } 10 (M = 4d or 5d element) species with its large NÀ RuÀ N angle and the "repulso" arrangement of the nitrosyls (which means that the slight deviation of the RuÀ NÀ O function from linearity results in an outward tilt of both NO ligands). Due to the only small deviation of the RuNO angle from 180°, 1 is an example of a dinitrosyl with two linear MNO functions.…”

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

“…Erst vor Kurzem klassifizierten Ghosh und Conradie Dinitrosylstrukturen nach elektronischen und geometrischen Parametern. [14] 1 folgt ihren Regeln für Spezies des Typs {M(NO) 2 } 10 (M = 4d-oder 5d-Element) mit seinem großen NÀ RuÀ N-Winkel und der "repulso"-Anordnung der Nitrosylliganden (was bedeutet, dass die geringfügige Abweichung der RuÀ NÀ O-Funktionen von der Linearität einen kleinen Knick nach außen ergibt.) Wegen der nur geringen Abweichung des RuNO-Winkels von 180°ist 1 ein Beispiel eines Dinitrosyls mit zwei linearen MNO-Funktionen, kurz: 1 ist eine (l-NO-kN) 2 -Spezies.…”

“…Erst vor Kurzem klassifizierten Ghosh und Conradie Dinitrosylstrukturen nach elektronischen und geometrischen Parametern [14] . 1 folgt ihren Regeln für Spezies des Typs {M(NO) 2 } 10 (M = 4d‐ oder 5d‐Element) mit seinem großen N−Ru−N‐Winkel und der “repulso”‐Anordnung der Nitrosylliganden (was bedeutet, dass die geringfügige Abweichung der Ru−N−O‐Funktionen von der Linearität einen kleinen Knick nach außen ergibt.)…”