Steering Single-Electron Metal–Metal Bonds and Hyperfine Coupling between a Transition Metal-Lanthanide Heteronuclear Bimetal Confined in Carbon Cages

Abstract

Metal complexes bearing single-electron metal–metal bonds (SEMBs) exhibit unusual electronic structures evoking strong magnetic coupling, and such bonds can be stabilized in the form of dimetallofullerenes (di-EMFs) in which two metals are confined in a carbon cage. Up to now, only a few di-EMFs containing SEMBs are reported, which are all based on a high-symmetry icosahedral ( I h ) C 80 cage embedding homonuclear rare-earth bimetals, and a chemical modification of the I h -C 80 cage is required to stabilize the SEMB. Herein, by introducing 3d-block transition metal titanium (Ti) along with 4f-block lanthanum (La) into the carbon cage, we synthesized the first crystallographically characterized SEMB-containing 3d–4f heteronuclear di-EMFs based on pristine fullerene cages. Four novel La–Ti heteronuclear di-EMFs were isolated, namely, LaTi@ D 3 h (5)-C 78, LaTi@ I h (7)-C 80, LaTi@ D 5 h (6)-C 80, and LaTi@ C 2 v (9)-C 82, and their molecular structures were unambiguously determined by single-crystal X-ray diffraction. Upon increasing the cage size from C 78 to C 82, the La–Ti distance decreases from 4.31 to 3.97 Å, affording fine-tuning of the metal–metal bonding and hyperfine coupling, as evidenced by an electron spin resonance (ESR) spectroscopic study. Density functional theory (DFT) calculations confirm the existence of SEMB in all four LaTi@C 2 n di-EMFs, and the accumulation of electron density between La and Ti atoms shifts gradually from the proximity of the Ti atom inside C 78 to the center of the LaTi bimetal inside C 82 due to the decrease of the La–Ti distance. The electronic properties of LaTi@C 2 n heteronuclear dimetallofullerenes differ apparently from their homonuclear La 2 @C 2 n counterparts, revealing the peculiarity of heteronuclear dimetallofullerenes with the involvement of 3d-block transition metal Ti.

Topics & Concepts