Computational Design and Theoretical Properties of WCN, an H-Free Melaminate and Potential Multifunctional Material.

By means of first-principles theory, existence, synthetic conditions, and structural as well as physicochemical properties have been predicted for the first hydrogen-free melaminate salt of the composition WCN. We find at least two energetically favorable polymorphs adopting space groups 1 and 3, both of which are layer-like porous materials. In addition to sizable Madelung fields stabilizing saltlike WCN, the complex CN anions are connected via perfectly optimized W-N bonds, forming WN in the 1 and WN coordination polyhedra in the 3 polymorphs. The band gaps of the 1 and 3 phases are HSE-predicted as 2.25 and 1.21 eV, respectively, significantly smaller than those of g-CN and WO. Moreover, both phases have suitable band-edge potentials that may provide sufficient driving force for photocatalytic water splitting; at least for the 1 phase, there is also a reasonable chance for reduced electron-hole recombination. In addition, the polymorphs's large optical absorption coefficients should greatly enhance the photocatalytic performance. WCN defines a new class of compounds and has unique structural characteristics, mirrored from its electrical and optical properties, and it should provide another chemical path for preparing efficient photocatalysts and optoelectronic devices.