Identifying a Needle in a Haystack: Isolation and Structural Characterization of Er 2 C 94 as the Carbide Er 2 C 2 @ D 3 (85)‐C 92

Mass spectrometry for multi-dimensional characterization of natural and synthetic materials at the nanoscale

Characterization of materials at the nanoscale plays a crucial role in in-depth understanding the nature and processes of the substances. Mass spectrometry (MS) has characterization capabilities for nanomaterials (NMs) and nanostructures by offering reliable multi-dimensional information consisting of accurate mass, isotopic, and molecular structural information. In the last decade, MS has emerged as a powerful nano-characterization technique. This review comprehensively summarizes the capabilities of MS in various aspects of nano-characterization that greatly enrich the toolbox of nano research. Compared with other characterization techniques, MS has unique capabilities for real-time monitoring and tracking reaction intermediates and by-products. Moreover, MS has shown application potential in some novel aspects, such as MS imaging of the biodistribution and fate of NMs in animals and humans, stable isotopic tracing of NMs, and risk assessment of NMs, which deserve update and integration into the current knowledge framework of nano-characterization.

Crystallographic characterization of Er2C2@C2(43)-C90, Er2C2@C2(40)-C90, Er2C2@C2(44)-C90, and Er2C2@C1(21)-C90: the role of cage-shape on cluster configuration

For endohedral metallofullerenes (EMFs), that is, fullerenes encapsulating metallic species, cage size is known to be an important factor for cluster configuration adoption; however, the impact of the cage shape on the cluster geometry fitting remains poorly understood. Herein, for the first time, four dierbium-carbide EMFs with C₉₀ cages, namely, Er₂C₂@C₂(43)-C₉₀, Er₂C₂@C₂(40)-C₉₀, Er₂C₂@C₂(44)-C₉₀, and Er₂C₂@C₁(21)-C₉₀, were successfully synthesized and fully characterized using a combination of mass spectrometry, single-crystal X-ray diffractometry, vis-NIR, Raman and photoluminescence spectroscopies, and cyclic voltammetry. In particular, the fullerene cages of C₂(43)-C₉₀ and C₂(44)-C₉₀ are crystallographically identified for the first time. Interestingly, the ErEr distance of the major sites in Er₂C₂@C₂(43)-C₉₀, Er₂C₂@C₂(40)-C₉₀, Er₂C₂@C₂(44)-C₉₀, and Er₂C₂@C₁(21)-C₉₀ is 3.927, 4.058, 4.172, and 4.651 Å, respectively, which increases gradually with an increase in the major axis of the cage. Moreover, the bond length of the inner C₂-unit decreases progressively with an increase in the ErEr distance, indicating that the inserted C₂-unit can serve as a molecular spring to support the strong metal-cage interactions within cages with the same size but different shapes. Hence, the role of cage shape on the cluster configuration is unveiled safely for the as-obtained Er₂C₂@C₉₀ isomers.

Crystallographic characterization of Lu2C2n (2n = 76-90): cluster selection by cage size

The successful isolation and unambiguous crystallographic assignment of a series of lutetium-containing endohedral metallofullerenes (EMFs), Lu2C2n (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@C2n (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@C2n (2n = 86, 88). Consistently, our theoretical results reveal that all these EMFs are thermodynamically favorable isomers. Thus the comprehensive characterization of the series of Lu2C76-90 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.

Isolation and Structural Characterization of Er@ C2 v(9)-C82 and Er@ C s(6)-C82: Regioselective Dimerization of a Pristine Endohedral Metallofullerene Induced by Cage Symmetry

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-.

Crystallographic characterization of Y2C2n (2n = 82, 88–94): direct Y–Y bonding and cage-dependent cluster evolution

The long-sought Y–Y bonding is experimentally observed in organometallic complexes for the first time by encapsulation inside the hollow cavity of C_3v(8)-C₈₂ and C_s(6)-C₈₂ fullerene cages.