Coordination of N2 ligands to lanthanum: the complexes La (N2)1–8

Abstract

The structures and bonding properties of La(N 2 ) 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 N 2 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 N 2 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, N 2 ) leading to electrostatic attractive interactions which compose the minor contribution in the bonding.Very recently, Zhao et al. studied the whole lanthanide series of Ln(N 2 ) molecules using the mPW3PBE hybrid exchange-correlation functional in conjunction with quasirelativistic 4f-in-valence pseudopotentials for the lanthanides and 6-31G* basis set for nitrogen [29]. The covered molecular properties were the geometries, HOMO-LUMO energy gaps, and magnetic and electronic properties. These calculations predicted the end-on 4 La(N 2 ) structure to be favoured by 47 kJ/mol over 2 La(N 2 ) with a side-on structure. From the bonding properties, the π-type HOMO orbital and the atomic charges were presented.Teng and Xu performed DFT calculations using the BP86 and B3LYP functionals in order to assist the interpretation of the matrix-isolation IR spectra of the reaction products formed by laser-ablated La co-deposited with N 2 [23]. In the spectra, several species were identified and their electronic structures, dissociation energies and vibrational data were reported. On the basis of isotope experiments and computed data, the authors concluded on the dominant presence of end-on 4 La(N 2 ) in the argon matrix.The only theoretical study on complexes of a lanthanide atom with more than one N 2 ligands is an early SCF/3-21G computational study of holmium complexes by Ermilov et al.[30] using a 4f-in-valence pseudopotential [31] for Ho. Beyond the low-quality computational level, this study has also other limitations: only quartet spin multiplicity and complexes up to six N 2 ligands were considered. However, the small energy difference between the quartet and sextet Ho [32] may readily be overcompensated by N 2 bonding, particularly in the larger complexes. Therefore, the sextet Ho(N 2 ) x species should not be neglected. (Note that Zhao et al., in contrast, studied only the sextet HoN 2 [29].) Most striking is, however, the instability of HoN 2 at the SCF/3-21G l...

Structure and bonding of lanthanide dinitrogen complexes, Ln(N2)1‐8

“…Indeed, test calculations in the previous study on La(N 2 ) x complexes indicated several orbitals with negligible populations and concluded on the proper performance of the 7e/10o and 11e/12o active spaces for La(N 2 ) and La(N 2 ) 2 , respectively. [29] Analogously, in the present study, the active spaces of 7e/10o and 11e/12o were used for Lu(N 2 ) and Lu(N 2 ) 2 , respectively, including the 6s and all the 5d orbitals of Lu. The contribution of the main electron configuration to the wavefunction was 84% in 2 Lu(N 2 ) 2 , while it was over 92% in the other three Lu(N 2 ) x (x = 1, 2) species.…”

“…Ln interaction) resulting in positive charges of the Ln donors. [29,30] The following general observations can be made on the basis of Table 1: 1. In contrast to the analogous structures found generally in organometallic complexes across the Ln row, [66,67] there are some differences in the structures of the Ln(N 2 ) x complexes.…”

“…A recent study on La(N 2 ) x (x = 1-8) complexes showed that the generally small energy differences between the low-energy spin multiplicities of lanthanide atoms [28] can readily be overcompensated by N 2 bonding, particularly in the larger complexes. [29] In addition, lanthanide atoms were predicted to coordinate up to eight N 2 ligands. [29]…”

“…show some deviations from those of the other two studies. [20,29] Altogether, the description of lanthanide dinitrogen complexes is rather poor, lacking reliable information on the complexes having more than one N 2 ligands and, particularly, on the effect of 4f population on the properties of the complexes. This is the main goal of the present theoretical study, that is, to determine the structural, energetic, and bonding properties of lanthanide dinitrogen Ln(N 2 ) x (x = 1-8) complexes by state-of-the-art quantum chemical calculations.…”

“…From the possible coordination modes (end-on, side-on, and mixed side-on/end-on [31] ), only the end-on conformations were considered because of the demonstrated general preference of this structure in transition metal and lanthanide N 2 complexes. [14,16,[20][21][22][23][24]29,[31][32][33][34][35] 2 | COMPUTATIONAL DETAILS The DFT computations have been performed with Gaussian09 [36] applying the B3LYP [37,38] exchange-correlation functional in conjunction with the quasirelativistic small-core 4f-in-valence pseudopotential. [39] The valence basis set had a contraction scheme of [14s13p10d8f6g]/…”