Tetrazine-Based Ligand Transformation Driving Metal–Metal Bond and Mixed-Valence Hg(I)/Hg(II)

[Image: see text] Understanding the self-assembly of cluster aggregates remains an important challenge in coordination chemistry. A chelating tetrazine-based ligand was employed to isolate an unprecedented tetranuclear Hg(4) complex exhibiting Hg(I)/Hg(II) mixed valence, which also contains metal–metal bonds. Single-crystal X-ray diffraction, X-ray photoelectron spectroscopy, solid-state nuclear magnetic resonance, and theoretical approaches (density functional theory) were employed to shed some light on the structure and self-assembly of this discrete molecule.