Mixed dysprosium-lanthanide nitride clusterfullerenes DyM2N@C80-Ih and Dy2MN@C80-Ih (M = Gd, Er, Tm, and Lu): synthesis, molecular structure, and quantum motion of the endohedral nitrogen atom.

C Schlesier,F Liu,V Dubrovin,L Spree,S M Avdoshenko,A A Popov,B Büchner

doi:10.1039/c9nr03593a

Abstract

Systematic exploration of the synthesis of mixed-metal Dy-M nitride clusterfullerenes (NCFs, M = Gd, Er, Tm, Lu) is performed, and the impact of the second metal on the relative yield is evaluated. We demonstrate that the ionic radius of the metal appears to be the main factor allowing explanation of the relative yields in Dy-M mixed-metal systems with M = Sc, Lu, Er, and Gd. At the same time, Dy-Tm NCFs show anomalously low yields, which is not consistent with the relatively small ionic radius of Tm3+ but can be explained by the high third ionization potential of Tm. Complete separation of Dy-Gd and Dy-Er, as well as partial separation of Dy-Lu M3N@C80 nitride clusterfullerenes, is accomplished by recycling HPLC. The molecular structures of DyGd2N@C80 and DyEr2N@C80 are analyzed by means of single-crystal X-ray diffraction. A remarkable ordering of mixed-metal nitride clusters is found despite similar size and electronic properties of the metals. Possible pyramidalization of the nitride clusters in these and other nitride clusterfullerenes is critically analyzed with the help of DFT calculations and reconstruction of the nitrogen inversion barrier in M3N@C80 molecules is performed. Although a double-well potential with a pyramidal cluster structure is found to be common for most of them, the small size of the inversion barrier often leads to an apparent planar structure of the cluster. This situation is found for those M3N@C80 molecules in which the energy of the lowest vibrational level exceeds that of the inversion barrier, including Dy3N@C80 and DyEr2N@C80. The genuine pyramidal structure can be observed by X-ray diffraction only when the lowest vibrational level is below the inversion barrier, such as those found in Gd3N@C80 and DyGd2N@C80. The quantum nature of molecular vibrations becomes especially apparent when the size of the inversion barrier is comparable to the energy of the lowest vibrational levels.

Highlights

Nitride clusterfullerenes (NCFs), i.e. metallofullerenes with endohedral M3N clusters, are the most abundant and versatile family of endohedral clusterfullerenes.[1]
In the CeLu2N@C80·NiII(OEP)·2C7H8 crystal (CeLu2N@C80-Ih is the only non-Sc mixed-metal NCF studied by single-crystal X-ray diffraction before this work), the larger Ce atom is located further away from the NiII(OEP), and smaller Lu atoms are located closer to the porphyrin.12b We have recently studied the ordering of the endohedral cluster in Sc3N@C80 and YSc2N@C80 by NiII(OEP) theoretically and found that the ordering can be explained by simple electrostatic consideration based on the distribution of the electrostatic potential in the molecules.[28]
In this work we have undertaken a systematic exploration of various Dy-lanthanide combinations in the synthesis of mixedmetal nitride clusterfullerenes

Summary

Introduction

Nitride clusterfullerenes (NCFs), i.e. metallofullerenes with endohedral M3N clusters, are the most abundant and versatile family of endohedral clusterfullerenes.[1]. The Er3N and Lu3N clusters are nearly planar, whereas for Dy3N the experimental data allow two alternative interpretations: one suggests a planar cluster and a single nitrogen site, in which the thermal ellipsoid is strongly elongated in the out-of-plane direction.[31] A more recent interpretation of the same diffraction data suggests splitting of the nitrogen position between two sites leading to a pyramidal Dy3N cluster.6b In Gd3N@C80, a further increase of the metal size results in an average Gd–N bond length of 2.08 Å, and the

Results

Conclusion