Coordination of N2 ligands to lanthanum: the complexes La (N2)1\u20138

Attila Kovács

doi:10.1007/s11224-018-1177-2

Abstract

The structures and bonding properties of La(N2)x (x = 1–8) complexes were investigated by density functional theory (DFT) computations using the B3LYP exchange-correlation functional in conjunction with a quasi-relativistic pseudopotential for La. The quality of the DFT electronic structures was confirmed in selected cases by relativistic multireference calculations using CASPT2 theory. From the end-on and side-on dinitrogen coordination modes in general, the structures with end-on coordination were found to be the more stable. The first coordination sphere of the complexes is filled by eight and six N2 ligands in the end-on and side-on type species, respectively. The main bonding interaction is the donation of La 5d valence electrons to anti-bonding orbitals of N2 resulting in characteristic elongation of the NN bonds. These directional interactions determine the (from steric point of view in several cases less logic) equilibrium molecular structures. The charge transfer resulted in partial charges up to 1.5 e of the originally neutral components (La, N2) leading to electrostatic attractive interactions which compose the minor contribution in the bonding.

Highlights

Since the discovery of the Haber-Bosch process in 1909, considerable efforts are focused on the basic understanding of nitrogen fixation
An important step in this research was the discovery of the first ruthenium dinitrogen complexes in the 1960s and since strenuous efforts were made on the synthesis of transition metal dinitrogen complexes [1, 2]
As the complexes are formed from neutral La atom and N2 molecules, the arrangements of the N2 ligands around La are governed by orbital interactions

Summary

Introduction

Since the discovery of the Haber-Bosch process in 1909, considerable efforts are focused on the basic understanding of nitrogen fixation. Based on the observed occupations [51] and cost considerations in case of the larger model structures, the following active spaces (electron/orbital) were applied in the calculations of the various structures: 7/10 for La(N2) while 11/12 for La(N2) and La(N2). Based on the observed occupations [51] and cost considerations in case of the larger model structures, the following active spaces (electron/orbital) were applied in the calculations of the various structures: 7/10 for La(N2) while 11/12 for La(N2) and La(N2)6 For these CASPT2 calculations, the MOLCAS 8.2 code [52, 53] was applied. The minor contributions in the multi-determinant wavefunction appeared only by a few percent, suggesting that the title molecular systems can be reasonably modelled by DFT This refers to the structure and bonding interactions. The mostly very small energy differences between the doublet and quartet forms should be treated with caution

Results and discussion

Conclusions

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