Alkaline earth metal mediated inter-molecular magnetism in perfluorocubane dimers and chains

TL;DR

This study demonstrates how stacking arrangements and alkaline earth metal intercalation can tune the magnetic interactions in perfluorocubane dimers and chains, revealing new magnetic states and electronic properties.

Contribution

It uncovers the mechanisms by which stacking and intercalation influence intermolecular magnetism in perfluorocubane, introducing halogen bond-dominated exchange as a key factor.

Findings

Magnetic groundstates are tunable from AFM to FM via stacking and intercalation.

Intercalation with Na or Mg induces FM direct exchange and local magnetic moments.

Emergence of spin gapless semiconductor and charge density wave states in 1D chains.

Abstract

Perfluorocubane ($C_8F_8$) was successfully synthesized and found to accept and store electrons in its internal cubic cavity to form magnetic moments. However their inter-molecule spin-exchange coupling mechanism is yet to be revealed. In this study, we found the inter-molecule magnetic groundstates of $C_8F_8$ dimer and one-dimensional (1D) chain are tunable from antiferromagnetic (AFM) to ferromagnetic (FM) by stacking orders and alkaline earth metals intercalation using first-principle calculations. The inter-molecule couplings are dominated by noncovalent halogen $C-F...C_4$ interactions. Stacking orders of dimers can regulate the relative position of the lone pairs and $\sigma-holes$ at the molecular interface and thus the magnetic groundstates. Alkaline earth metals M (M = Na, Mg) intercalations could form $C_4-M-C_4$ bonds and lead to FM direct exchange at the inter-molecule region. An unpaired electron donated by the intercalated atoms or electron doping can result in a local magnetic moment in dimers, exhibiting an on-off switching by the odd-even number of electron filling. Novel electronic properties such as spin gapless semiconductor and charge density wave (CDW) states emerge when $C_8F_8$ molecules self-assemble with intercalated atoms to form 1D chains. These findings manifest the roles of stacking and intercalation in modifying intermolecular magnetism and the revealed halogen bond-dominated exchange mechanisms are paramount additions to those previously established non-covalent couplings.