Shuaifeng Hu

Abstract:

A series of Er-based nitride clusterfullerenes (NCFs), Er₃N@C_80-88, have been successfully synthesized and isolated. In particular, Er₃N@I_h(7)-C₈₀, Er₃N@D_5h(6)-C₈₀, Er₃N@C_2v(9)-C₈₂, Er₃N@C_s(51365)-C₈₄, and Er₃N@D₂(35)-C₈₈ have been characterized by single-crystal X-ray diffraction (XRD) for the first time. The planar configuration of the inserted Er₃N cluster is identified unambiguously and the Er-N distances increase in accordance with cage expansion to maintain strong metal-cage interactions. Additionally, the electrochemical properties of the Er₃N@C_80-88 series are studied by means of cyclic voltammetry. It is found that the first reduction potentials are roughly similar for all compounds under study, while the first oxidation potentials are cathodically shifted along with the increase of the cage size in the Er₃N@C_2n (2n = 80, 84, 86, 88) series, leading to a decrease in the corresponding electrochemical band gaps. Nevertheless, for Er₃N@C_2v(9)-C₈₂, a good electron donating ability is manifested by its relatively small first oxidation potential, which results from the relatively higher energy level of the highest occupied molecular orbital. The redox behaviors observed in such Er₃N-based NCFs may promise their great potential applications in donor-acceptor systems.

Abstract:

Two Er@C₈₂ isomers have been isolated and unambiguously characterized as Er@ C_{2 v}(9)-C₈₂ and Er@ C _s(6)-C₈₂, respectively, by single-crystal X-ray diffraction. Er@ C _s(6)-C₈₂ is identified as a dimeric structure in the crystalline state, but dimerization does not occur for Er@ C_{2 v}(9)-C₈₂ under identical crystallization conditions, indicating a cage-symmetry-induced dimerization process. Density functional theory calculations reveal that the major unpaired spin resides on a special C atom of Er@ C _s(6)-C₈₂, which leads to regioselective dimerization. Calculations also found that the dimeric structure of Er@ C _s(6)-C₈₂·Ni(OEP) is much more stable than the two monomers, suggesting a thermodynamically favorable dimerization process. Vis-near-IR spectrometric and electrochemical results demonstrate that the electronic structure of Er@C₈₂ isomers is Er³⁺@C₈₂^3-, instead of the theoretically proposed Er²⁺@C₈₂^2-.

Abstract:

The successful isolation and unambiguous crystallographic assignment of a series of lutetium-containing endohedral metallofullerenes (EMFs), Lu₂C_2n (2n = 76, 78, 80, 84, 86, 88, 90), reveal an unrecognized decisive effect of the cage size on the configuration of the encapsulated clusters. The molecular structures of these compounds are unambiguously assigned as Lu₂@T _d(2)-C₇₆, Lu₂@D _3h(5)-C₇₈, Lu₂@C _2v(5)-C₈₀, Lu₂@C _2v(7)-C₈₄, Lu₂@C _s(8)-C₈₆, Lu₂@C _s(15)-C₈₆, Lu₂@C ₁(26)-C₈₈, Lu₂C₂@C _2v(9)-C₈₆, Lu₂C₂@C _s(32)-C₈₈ and Lu₂C₂@D ₂(35)-C₈₈. Specifically, when the cage is relatively small, Lu₂@C_2n (2n = 76-86) are all dimetallofullerenes (di-EMFs) and a Lu-Lu single bond could be formed between the two lutetium ions inside the cages. However, when the cage expands further, the valence electrons forming the possible Lu-Lu bond donate to a readily inserted C₂-unit, resulting in the formation of carbide EMFs, Lu₂C₂@C_2n (2n = 86, 88). Consistently, our theoretical results reveal that all these EMFs are thermodynamically favorable isomers. Thus the comprehensive characterization of the series of Lu₂C_76-90 isomers and the overall agreement between the experimental and theoretical results reveal for the first time that the exact configuration of the internal metallic cluster is determined by the cage size, taking a solid step towards the controlled synthesis of novel hybrid molecules which may have potential applications as building blocks of single molecule devices.

Abstract:

The small Sc₃ N cluster has only been found in such small cages as C_2n (2n=68, 78, 80, 82), whereas the large M₃ N (M=Y, Gd, Tb, Tm) clusters choose those larger cages C_2n (2n=82-88). Herein, concrete experimental evidence is presented to establish the size effect of the internal metallic cluster on selecting the outer cage of endohedral metallofullerenes (EMFs) by using a medium-sized metal, lutetium, which possesses an ionic radius between Sc and Gd. A series of lutetium-containing EMFs have been obtained and their structures are unambiguously determined as Lu₃ N@I_h (7)-C₈₀ , Lu₃ N@D_5h (6)-C₈₀ , Lu₃ N@C_2v (9)-C₈₂ , Lu₃ N@C_s (51365)-C₈₄ , Lu₃ N@D₃ (17)-C₈₆ , and Lu₃ N@D₂ (35)-C₈₈ by single-crystal X-ray diffraction crystallography. It was confirmed that the encaged Lu₃ N cluster always adopts a planar geometry in Lu₃ N@C_80-88 isomers to ensure substantial metal-cage/metal-nitrogen interactions. As a result, the Lu₃ N cluster selects the C_2v (9)-C₈₂ cage, which also encapsulates Sc₃ N, instead of the C_s (39663)-C₈₂ cage which is more suitable for M₃ N (M=Y, Gd, Tb, Tm). However, different from Sc₃ N, Lu₃ N can also template the C_84-88 cages which are absent for Sc₃ N-containing EMFs, confirming clearly the size effect of the internal cluster on selecting the outer cage.