A theoretical and experimental approach to the optical response and the electronic structure of Hg¹⁺ and Hg²⁺ nitroprussides

Transition metal nitroprussides have an n-type semiconductor electronic behavior whose optical response remains scarcely documented. Experimentally, their electronic structure is dominated by Metal to Ligand Charge Transfer (MLCT) type transition that arises from the nitroprusside moiety, [Fe(CN)₅NO]^2-. In addition to that optical transition, these materials can absorb light from d-d and band-band transitions. In this contribution, the electronic structure of monovalent, Hg₂[Fe(CN)₅NO]⋅2H₂O, and divalent mercury, Hg[Fe(CN)₅NO] is studied using ab-initio calculations and experimental results. Results from UV–Vis, IR, and Raman spectroscopies revealed the nature of the electronic transitions that explain the optical response of mercury nitroprusside systems. For the studied systems, the wide optical bandgap is revisited, and new values are reported. The influence of the valence of the mercury ion on the electronic structure and its changes according to the structural features are analyzed. The employed Meta-GGA functional SCAN and SCAN ​+ ​rVV10 proved to be accurate methods to describe the structure and electronic properties of the studied mercury nitroprusside-based materials at a reasonable computational cost.