Synthesis and Electronic Structure of a 3D Crystalline Stack of MXene-like Sheets

Despite the interest in MXenes in the last decade, MXenes are often highly disordered, which can complicate their study and use. For example, nearly all MXenes have a random mixture of surface terminations (-O, -OH, -F). In addition, restacked 3D films have turbostratic disorder and often contain ions, solvent, and other species in between their layers. Here, we report Y2CF2, a layered crystal with a unit cell isostructural to a MXene, in which layers are capped only by fluoride anions. We directly synthesize the 3D crystal through a high-temperature solid-state reaction, which affords the 3D crystal in high yield and purity and ensures that only fluoride ions terminate the layers. We characterize the crystal structure and electronic properties using a combination of experimental and computational techniques. We find that relatively strong electrostatic interactions bind the layers together into a 3D crystal and further find that the lack of orbital overlap between layers gives rise to a description of Y2...