Magnetic Dioxygen Clathrate Hydrates: A Type of Promising Building Blocks for Icy Crystalline Materials

Clathrate hydrates (CHs) have recently attracted considerable research interest in fundamental science and practical applications because guest molecules with special electronic properties can be selectively trapped in the hydrogen-bonded water cages, and thus such CHs could be a novel class of promising functional materials. However, information about the electronic properties of CHs containing paramagnetic guest molecules and the spin-coupling mechanisms are quite scarce. In this work, at the ab initio molecular dynamics level, we first simulate the magnetic properties and spin-coupling mechanism of the structure I-type double O-2 CHs (O-2@CHs) derived from the experimental crystal structure. The results show that these O-2@CHs exhibit rich diversity of spin-coupling characteristics, depending on the O-2-occupation patterns of the nanocages and relative orientations of two O-2, which govern the orbital overlaps between the spin carriers. O-2@CHs presents the antiferromagnetic coupling when two guest O-2 are encapsulated in two symmetric 5(12)6(2) cages or one 5(12)6(2) cage with parallel orientations, whereas it exhibits the paramagnetic state for all other population patterns. The direct O-2 center dot center dot center dot O-2 spin couplings operate through the diffuse parts of the O-2 orbitals in these systems. Further, the elastic strain is examined for tuning their magnetic properties, finding that spin arrangement and magnetic characteristics can reversibly convert between the antiferromagnetic [up arrow(up arrow)...down arrow(down arrow)...up arrow(up arrow)...down arrow(down arrow)...](n) and ferromagnetic [up arrow...up arrow...up arrow...up arrow...](n) mode with nonlinear responses under isotropic strain between -7 and 20%. Under the compression strain, the increased spin polarization from the guest O-2 to the host cage supports the O-2 center dot center dot center dot O(host)center dot center dot center dot O-2 superexchange coupling mediated by the hosting water network as a coexisting coupling pathway, which plays a key role in improving the magnetic coupling. These intriguing findings here are expected to provide helpful information for developing novel CHs-based icy crystal magnetic nanomaterials.