Confinement-Driven Redox Inversion and Predicted Ferromagnetism in One-Dimensional Sc3Cl8 within Single-Walled Carbon Nanotubes.

Single-walled carbon nanotubes (SWCNTs) act as one-dimensional (1D) nanoreactors capable of stabilizing reactive species and unique low-dimensional phases. Here, we report the synthesis of an unprecedented 1D Sc3Cl8 phase formed via the confinement-induced structural reconstruction of bulk ScCl3 within SWCNTs. The atomic structure of the Sc3Cl8@SWCNT heterostructure is determined by combining aberration-corrected electron microscopy (HRTEM/STEM) with machine-learning force field (MLFF) global structure searches. This reconstruction yields a metal-rich phase that exhibits two anomalous properties. First, unlike typical halide fillers that induce p-type doping, the Sc3Cl8 chain acts as a potent electron donor, driving a strong n-type charge transfer to the nanotube host (a phenomenon we term "redox inversion"). Second, spin-polarized density functional theory (DFT) predicts that the confined chain possesses a ferromagnetic ground state, emerging from a diamagnetic bulk precursor. These results identify Sc3Cl8@SWCNTs as a model heterostructure where confinement simultaneously inverts doping polarity and unlocks magnetic potential, offering a new platform for carbon-based spintronics.