Hydroxide-Enhanced Superexchange Magnetic Couplings in Ionic Clathrate Hydrates

Abstract

The guest-driven magnetic properties of clathrate hydrates (CHs) has a promising application prospect as a new type of icy magnetic material, but it meets more difficulties for practical applications due to its weak spin coupling character. Through examining three different O2 CHs, O2@CHs, ionic diethyl­dimethylammonium hydroxide + O2 CHs (O2·EMN+@CHs), and nonionic 2-methyltetrahydrofuran + O2 CHs (O2·MTHF@CHs), we computationally show that the doping of OH– in the host cavity can enhance the magnetic spin coupling and modify the magnetic characteristics through a superexchange pathway in the ionic clathrate hydrates of O2 (i.e., the magnetic exchange energy being −23 meV of O2·EMN+@CHs (antiferromagnetic) versus 0 meV of O2@CHs (paramagnetic) and 2 meV of O2·MTHF@CHs (ferromagnetic)). The antiferromagnetic superexchange coupling in O2·EMN+@CHs originates from the p-orbital mixing among guest O2 mediated by the p-type orbital of the OH–-doped host framework. Also interestingly, for O2·X@CH (X = EMN+OH–, MTHF), the compressive strain can significantly enhance the antiferromagnetic coupling, while the tension strain is favorable to the ferromagnetic one. This work verifies that incorporation of OH– into the host lattice and utilization of strain can tune the spin coupling strength and even switch the magnetic characteristics between the ferromagnetic and antiferromagnetic couplings and thus improve the performance of magnetic CHs. Clearly, the present work paves the way for understanding the nature of magnetic coupling interactions in ionic magnetic CHs and for the practical applications of such CHs as porous functional materials.