Encapsulation of diatomic molecules in fullerene C₆₀: implications for their main properties

Abstract

The endohedral complexes of diatomic guest molecules H2, N2, O2, F2, HF, CO, LiH, LiF, BN, and BeO with C60 have been characterized computationally by employing second-order Møller-Plesset (MP2) theory and its density-fitting local (DF-LMP2) variant. The interaction energies, equilibrium geometries, dipole moments and harmonic vibrational frequencies of these complexes have been systematically calculated. It was found that all guest molecules are stabilized inside the C60 cage, with the most pronounced stabilization effect (of about 50 kcal mol(-1)) observed for the polar covalent BeO and BN molecules. It is noteworthy that the normally short-lived BN molecule is the only guest molecule that was found to chemisorb on the inner surface of C60. When encapsulated, all guest molecules (except for BN) exhibit bond elongation (up to 0.07 Å) and, consequently, a red shift in vibrational stretching frequencies. In fact, the calculated vibrational properties of the H2@C60 complex agree well with those derived from experiment. The C60 geometry is not perturbed significantly upon encapsulation, but a subtle tendency to decrease the carbon-carbon bond alternation is observed. Polar guest molecules inside C60 are located at an off-center position and a significant decrease in their dipole moments upon encapsulation is observed. The importance of explicitly taking into account electron correlation effects, as well as full geometry relaxation, to yield a correct description of the complexes investigated is clearly demonstrated. The present results may serve as a guide for future attempts to synthesize such complexes employing the "molecular surgery" approach.

The dipolar endofullerene HF@C60

“…The obtained dipole moment is in good agreement with some theoretical estimates 17,18,20 and indicates that shielding by the fullerene cage reduces the dipole moment of HF@C 60 to about 25% of that for isolated HF. 42 …”

“…The change in the fundamental vibrational transition (-170.5 cm -1 ) is in excellent agreement with that calculated by Dolgonos (-174 cm -1 ), 17 31 The rotational redshifts are attributed to a coupling of translational and rotational modes inside the cavity, and to cage-host interactions, which cause the inertial moment of the HF molecule to acquire some of the effective mass of the cage. The vibrational red-shift is due to lengthening, of the bond of the enclosed diatomic molecule indicating an attractive interaction with the cage.…”

“…Predictions of the properties of HF@C 60 have been made using classical, 14 semiempirical 15,16 and quantum chemistry techniques. [17][18][19][20] Furthermore it has been postulated that endofullerenes containing freely rotating electric dipoles could exhibit ferroelectricity, due to cooperative alignment of the interacting electric dipole moments. 21…”

Gas storage of simple molecules in boron oxide nanocapsules

“…Encapsulation of atoms and molecules by fullerenes has been a subject of many experimental and theoretical works . Although a number of atomic endohedral complexes of C 60 are known, but encapsulation of molecules has been difficult.…”

“…The stability of endohedral complexes of fullerenes has been studied by various approaches, from semiempirical and molecular mechanic calculations, through Hartree–Fock (HF) and density functional theory (DFT) to recently developed supermolecular DFT with empirical dispersion corrections (DFT + Disp), symmetry‐adapted perturbation theory (SAPT), Møller–Plesset second‐order perturbation theory (MP2), spin‐component‐scaled MP2 (SCS‐MP2), and long‐range corrected MP2 (MP2C) methods . Recently, Dolgonos and Peslherbe, Kruse and Grimme, Korona et al and Sebastianelli et al calculated the interaction energy of the C 60 and C 70 with one and two hydrogen molecules inside using MP2, SCS‐MP2, DFT‐SAPT, and diffusion Monte Carlo calculations, respectively.…”