Structural, electronic, and magnetoresponsive properties of triangular lanthanide clusters and their free‐standing nitrides

Abstract

The molecular and electronic structures, stabilities, bonding features, and magnetoresponsive properties of three-membered [c-Ln(3)](+/0/-) (Ln = La, Ce, Pr, Nd, Gd, Lu) and heterocyclic six-membered [c-Ln(3)E(3)](q) (Ln = La, Ce, Pr, Nd, Gd, Lu; E = C, N; q = 0 or 1) rings have been investigated by means of electronic structure calculation methods at the DFT level. The [c-Ln(3)](+/0/-) clusters are predicted to be bound with respect to dissociation to their constituent atoms, the estimated binding energies ranging from 45.8 to 2056.4 kJ/mol. The [c-Ln(3)] rings capture easily a planar three-coordinated nitrogen atom at the center or above the center of the ring yielding the lanthanide nitride clusters [c-Ln(3)(μ(3)-N)] adopting a planar geometry, except [c-La(3)(μ(3)-N)] which exhibits pyramidal geometry. The [c-Ln(3)(μ(3)-N)] clusters are predicted to be bound, with respect to dissociation to N ((4)S) atom and [c-Ln(3)] clusters in their ground states, the binding energies ranging from 53.9 to 257.9 kcal/mol. The six-membered [c-Ln(3)E(3)](q) rings are predicted to be bound with respect to dissociation to LnE(q) monomers in their ground states with dissociation energies in the range of 173.8 to 318.0 kcal/mol. Calculation of the NICS(zz)-scan curves of the clusters predicted a "hermaphrodic" magnetic response of the [c-Ln(3)](+/0/-) and heterocyclic six-membered [c-Ln(3)E(3)](q) rings, manifested by the coexistence of successive diatropic (aromatic) and paratropic (antiaromatic) zones. The [c-La(3)](+/0/-) and [c-Lu(3)](-) are predicted to be weakly antiaromatic, the [c-Lu(3)](0/+), [c-Lu(3)C(3) ](+), and [c-Lu(3)N(3)] double (σ+π) aromatic, and the [c-Gd(3)C(3)] and [c-Gd(3)N(3)](+) rings (σ+δ)-aromatic systems.

Recent developments and future prospects of all-metal aromatic compounds

“…Tsipis et al 100 have discussed the f-aromaticity of a number of lanthanoid clusters [c-Ln 3 ] +/0/À , with Ln = La, Ce, Pr, Nd, Gd, and Lu. They have determined through DFT calculations that all these clusters have a perfect D 3h three-membered ring like ground state, very stable towards full atomization.…”

Theoretical studies on the bonding and electron structures of a [Au3Sb6]3− complex and its oligomers

“…1 indicate that, while the cyclo-Sb 3 + cation is both σand π-aromatic, 57,58 the Sb 3 − anionic fragment can be viewed as dual σ-aromatic as the electrons in the π-type MOs (a″ 2 + e″*) cancel out while the inplane σ-type bonding orbitals, 4a′ 1 (radial) and 5e′ (tangential), are completely occupied with the corresponding antibonding MOs fully empty. This scenario is reminiscent of the σ aromaticity in the cyclo-Hf 3 cluster, [59][60][61] π aromaticity in the C 3 H 3 + cation 62,63 and benzene, and cubic aromaticity in the [Zn(I) 8 ] cluster. 64 Similarly, the Sb 3 3− cluster can be viewed as partially aromatic, albeit with weakened π-type interaction, and can serve as stable ligands in binding with other metal atoms through stabilization of the vertical 3e′ HOMO.…”

σ-Aromaticity in Hexa-Group 16 Atom-Substituted Benzene Dications: A Theoretical Study

“…The isotropic NICS values (NICS iso ) and their zz components (NICS zz ) were computed employing the GIAO method with the BS2 basis set. Though NICS zz values are considered to be better indexes for aromaticity of plane molecules than NICS iso values , and show positive linear correlation as shown in Supporting Information. To examine the dependence of calculation methods, we compared other basis sets and functionals, such as M062X and BLYP-D3. − (see Supporting Information) The optimized structures, singlet–triplet energy differences, and NICS values did not depend much on the computational methods.…”

“…Though the typical aromaticity is shown in π-electron delocalized systems, many systems that show aromaticity caused by σ, δ, − and ϕ electrons have been reported. The concept of σ-aromaticity or double aromaticity caused by σ and π orbitals was first suggested for cyclic hydrocarbons by theoretical studies. − Nowadays, not only cyclic hydrocarbons but also hydrogen clusters − and metal clusters − are suggested to have σ-aromatic characters both from theoretical and experimental viewpoints.…”