Noncovalent dyads of lanthanide nitride cluster fullerenes Ln3N@C80 and bisphthalocyanines LnPc2: Insights from DFT calculations.

Abstract

Context: Lanthanide-based systems, such as nitride cluster fullerenes Ln₃N@C₈₀ and bipthalocyanines LnPc₂ (Pc = phthalocyanine ligand), are of interest for their magnetic, fluorescent and electronic properties. In this regard, we performed DFT characterization to investigate the changes in structure and electronic properties for noncovalently interacting lanthanide (Ln; where Ln = La, Ce, Gd and Lu) nitride cluster fullerenes and bisphthalocyanines to form Ln₃N@C₈₀ + LnPc₂ dyads. The optimized geometries, formation and frontier orbital energies, HOMO-LUMO plots, charge and spin of Ln and N(NCF) atoms, as well as spin density plots of the dyads were analyzed in comparison with those of isolated Ln₃N@C₈₀ and LnPc₂ components. In addition to LnPc₂ bending distortion, the noncovalent dyad formation alters the geometry of the encapsulated Ln₃N cluster, favoring more planar or pyramidal geometries, depending on the case. The HOMO and LUMO orbitals are found on bisphthalocyanines, being localized on the isoindole units, except for Ce₃N@C₈₀ + CePc₂ dyad, where the LUMO was found on the central metal of CePc₂. The HOMO-LUMO gap energy is lower for the dyads compared to isolated NCFs, being rather close to the gap energy of bisphthalocyanines. The changes in spin density distribution are evident in the dyads containing Ce and Gd atoms, contrary to their La and Lu-derived counterparts. The interaction of Ce₃N@C₈₀ and Gd₃N@C₈₀ with CePc₂ and GdPc₂, respectively, causes redistribution of the spin density, with changes in the orientation of spin-up and spin-down electrons in the encapsulated Ce₃N and Gd₃N clusters.

Methods: The geometry optimization and electronic properties calculations based on density functional theory were performed using the DMol³ module of Material Studio 8.0 software package from Accelrys Inc. The computational parameters selected included the general gradient approximation functional PBE, combined with a long-range dispersion correction developed by Grimme (PBE-D2), the double numerical basis set (DN), equivalent to the 6-31G Pople-type basis set along with the DFT semiconductor pseudopotentials. To mitigate the self-consistent field convergence problems, the thermal smearing technique was applied, with a final very small value of 0.0001 Ha (equivalent to 31.6 K temperature), or Fermi orbital occupancy in some cases.