Using internal strain and mass to modulate DyMIDLINE HORIZONTAL ELLIPSISDy coupling and relaxation of magnetization in heterobimetallic metallofullerenes DyM2N@C80 and Dy2MN@C80 (M = Sc, Y, La, Lu)

Endohedral clusters inside metallofullerenes experience considerable inner strain when the size of the hosting cage is comparably small. This strain can be tuned in mixed-metal metallofullerenes by combining metals of different sizes. Here we demonstrate that the internal strain and mass can be used as variables to control DyMIDLINE HORIZONTAL ELLIPSISDy coupling and relaxation of magnetization in Dy-metallofullerenes. Mixed-metal nitride clusterfullerenes DyxY3-xN@I-h-C-80 (x = 0-3) and Dy2LaN@I-h-C-80 combining Dy with diamagnetic rare-earth elements, Y and La, were synthesized and characterized by single-crystal X-ray diffraction, SQUID magnetometry, ab initio calculations, and spectroscopic techniques. DyxY3-xN clusters showed a planar structure, but the slightly larger size of Dy3+ in comparison with that of Y3+ resulted in increased elongation of the nitrogen thermal ellipsoid, showing enhancement of the out-of-plane vibrational amplitude. When Dy was combined with larger La, the Dy2LaN cluster appeared strongly pyramidal with the distance between two nitrogen sites of 1.15(1) angstrom, whereas DyLa2N@C-80 could not be obtained in a separable yield. Magnetic studies revealed that the relaxation of magnetization and blocking temperature of magnetization in the DyM2N@C-80 series (M = Sc, Y, Lu) correlated with the mass of M, with DySc2N@C-80 showing the fastest and DyLu2N@C-80 the slowest relaxation. Ab initio calculations predicted very similar g-tensors for Dy3+ ground state pseudospin in all studied DyM2N@C-80 molecules, suggesting that the variation in relaxation is caused by different vibrational spectra of these compounds. In the Dy2MN@C-80 series (M = Sc, Y, La, Lu), the magnetic and hysteretic behavior was found to correlate with DyMIDLINE HORIZONTAL ELLIPSISDy coupling, which in turn appears to depend on the size of M3+. Across the Dy2MN@C-80 series, the energy difference between ferromagnetic and antiferromagnetic states changes from 5.6 cm(-1) in Dy2ScN@C-80 to 3.0 cm(-1) in Dy2LuN@C-80, 1.0 cm(-1) in Dy2YN@C-80, and -0.8 cm(-1) in Dy2LaN@C-80. The coupling of Dy ions suppresses the zero-field quantum tunnelling of magnetization but opens new relaxation channels, making the relaxation rate dependent on the coupling strengths. DyY2N@C-80 and Dy2YN@C-80 were found to be non-luminescent, while the luminescence reported for DyY2N@C-80 was caused by traces of Y3N@C-80 and Y2ScN@C-80.

Automated summary

The internal strain and mass of metallofullerenes can be controlled to regulate the coupling and relaxation of magnetization in Dy-metallofullerenes. Mixed-metal nitride clusterfullerenes were synthesized and characterized, and magnetic studies revealed that the relaxation of magnetization correlated with the mass of the metal element. Ab initio calculations predicted different vibrational spectra of these compounds, leading to variations in relaxation.