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Author: Spree, Lukas × Subject: Fullerenes ×

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    Covalency versus magnetic axiality in Nd molecular magnets: Nd-photoluminescence, strong ligand-field, and unprecedented nephelauxetic effect in fullerenes NdM2N@C80 (M = Sc, Lu, Y)
    (Cambridge : RSC, 2023) Yang, Wei; Rosenkranz, Marco; Velkos, Georgios; Ziegs, Frank; Dubrovin, Vasilii; Schiemenz, Sandra; Spree, Lukas; de Souza Barbosa, Matheus Felipe; Guillemard, Charles; Valvidares, Manuel; Büchner, Bernd; Liu, Fupin; Avdoshenko, Stanislav M.; Popov, Alexey A.
    Nd-based nitride clusterfullerenes NdM2N@C80 with rare-earth metals of different sizes (M = Sc, Y, Lu) were synthesized to elucidate the influence of the cluster composition, shape and internal strain on the structural and magnetic properties. Single crystal X-ray diffraction revealed a very short Nd-N bond length in NdSc2N@C80. For Lu and Y analogs, the further shortening of the Nd-N bond and pyramidalization of the NdM2N cluster are predicted by DFT calculations as a result of the increased cluster size and a strain caused by the limited size of the fullerene cage. The short distance between Nd and nitride ions leads to a very large ligand-field splitting of Nd3+ of 1100-1200 cm−1, while the variation of the NdM2N cluster composition and concomitant internal strain results in the noticeable modulation of the splitting, which could be directly assessed from the well-resolved fine structure in the Nd-based photoluminescence spectra of NdM2N@C80 clusterfullerenes. Photoluminescence measurements also revealed an unprecedentedly strong nephelauxetic effect, pointing to a high degree of covalency. The latter appears detrimental to the magnetic axiality despite the strong ligand field. As a result, the ground magnetic state has considerable transversal components of the pseudospin g-tensor, and the slow magnetic relaxation of NdSc2N@C80 could be observed by AC magnetometry only in the presence of a magnetic field. A combination of the well-resolved magneto-optical states and slow relaxation of magnetization suggests that Nd clusterfullerenes can be useful building blocks for magneto-photonic quantum technologies.
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    Rotation of fullerene molecules in the crystal lattice of fullerene/porphyrin: C60 and Sc3N@C80
    (Cambridge : RSC, 2021) Hao, Yajuan; Wang, Yaofeng; Spree, Lukas; Liu, Fupin
    The dynamics of molecules in the solid-state is important to understand their physicochemical properties. The temperature-dependent dynamics of Sc3N@C80 and C60 in the crystal lattice containing nickel octaethylporphyrin (NiOEP) was studied with variable temperature X-ray diffraction (VT-XRD). The results indicate that the fullerene cages (both C60 and C80) in the crystal lattice present stronger libration than the co-crystallized NiOEP in the temperature range of 100–280 K. In contrast to the fullerene cage, the Sc3N cluster shows pronounced rotation roughly perpendicular to the plane of the co-crystallized NiOEP molecule driven by temperature. The obtained temperature dependent dynamic behavior of the Sc3N cluster is different from that of Ho2LuN and Lu3N, regardless of their rather similar structure, indicating the effect of the mass and size of the metal ions.