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Dinitrogen metal complexes with a strongly activated N-N bond: A computational investigation of [(Cy2N)3Nb-(μ-NN)-Nb(NCy2)3] and related [Nb-(μ-NN)-Nb] systems

Citation

Cavigliasso, G and Stranger, R and Yates, BF, Dinitrogen metal complexes with a strongly activated N-N bond: A computational investigation of [(Cy2N)3Nb-(μ-NN)-Nb(NCy2)3] and related [Nb-(μ-NN)-Nb] systems, Dalton Transactions, 41, (45) pp. 13948-13959. ISSN 1477-9226 (2012) [Refereed Article]

Copyright Statement

Copyright 2012 The Royal Society of Chemistry

DOI: doi:10.1039/c2dt31845h

Abstract

The structural and bonding properties of the dinitrogen-bridged diniobium [(Cy2N)3Nb(μ-NN)Nb(NCy2)3] complex experimentally characterized by Berno and Gambarotta, which exhibits a strongly activated NN bond of 134 pm, have been explored using density functional methods and compared with those of a series of related [(R2N)3Nb(μ-NN)Nb(NR2)3] (R = H, Me, iPr, tBu, Cy) model species and other experimentally relevant [Nb(μ-NN)Nb] systems, in order to rationalize the unusually long NN distance. Geometry optimizations of [(Cy2N)3Nb(μ-NN)Nb(NCy2)3] and three other known systems indicate that the most favourable NN distance lies within the range of commonly reported results for end-on bound dinitrogendiniobium complexes, between 123 and 128 pm. However, structures exhibiting appreciably longer NN distances, close to 134 pm, are found to be only weakly disfavoured, and may represent the preferred geometry in cases where lengthening of the NN bond counteracts the effects of highly repulsive steric interactions between terminal fragments. Calculations on model complexes, in which small-sized [R = H, Me] terminal groups are involved, support the finding that NN bond lengths within the 123128 pm range are most favoured, whereas calculations on larger [R = iPr, tBu] model species indicate that the presence of excessively repulsive intramolecular interactions can lead to substantial changes in the geometric properties of the [NbNNNb] core, including significant increase in NN bond length and activation. The preference for NN distances ranging between 123 and 128 pm, irrespective of ligand size and identity, can be understood on the basis that the principal bonding mechanisms across the central [NbNNNb] core are largely unaffected by changes in the chemical composition and properties of terminal fragments. However, the balance between repulsive (steric) and attractive (electrostatic plus orbital) bonding contributions can be altered by the presence of geometrically rigid and oversized peripheral groups and, in these cases, the interplay between repulsive and attractive bonding effects is dominated by the former and can result in abnormally elongated NN distances. The present calculations thus provide a rationale for the observed structural properties of the [(Cy2N)3Nb(μ-NN)Nb(NCy2)3] system on the basis of the interplay between electronic and steric factors.

Item Details

Item Type:Refereed Article
Keywords:bonding mechanism, bonding property, chemical compositions, computational investigation, density-functional methods, dinitrogen, geometric properties, geometry optimization, intramolecular interactions, model complexes, steric factor
Research Division:Chemical Sciences
Research Group:Inorganic Chemistry
Research Field:Transition Metal Chemistry
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Chemical Sciences
Author:Yates, BF (Professor Brian Yates)
ID Code:81606
Year Published:2012
Web of Science® Times Cited:3
Deposited By:Chemistry
Deposited On:2012-12-18
Last Modified:2016-10-26
Downloads:0

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