Tetradymites and tetradymite-like chalcogenides empowered by n-center (n ≥ 5) hybrid multicenter bonds

Recent work has demonstrated the existence of hybrid multicenter bonds (HMBs) that complement the two well-known multicenter bonds since 1950: the electron-rich multicenter bond (ERMB) and electron-deficient multicenter bond (EDMB). HMBs have been described as mixed ERMBs and EDMBs, have been found in the linear or quasi-linear I5 – anion, and have been predicted to occur in the linear or quasi-linear I2n+1 – (n > 2) anions. Tetradymites, by contrast, are layered low-bandgap semiconductors whose extraordinary properties have previously been attributed to either intralayer EDMBs (metavalent bonds) or ERMBs (hypervalent bonds). In this work, we solve this longstanding debate by calculating crystal bond indices up to 11 atoms and demonstrating that tetradymites and tetradymite-related materials, including B2X3 (quintuple layers), AB2X4 (septuple layers), A2B2X5 (nonuple layers), and A3B2X6 (eleven-tuple layers) families (A=group-14; B=group-15; and X=group-16 elements), feature quasi-linear HMBs extending across five, seven, nine, and eleven atoms, respectively. In particular, quintuple-layer tetradymites exhibit the simplest HMBs, composed of one EDMB inserted on one ERMB. This finding confirms that HMBs exist in extended solids, not just in isolated I5 anions. To our knowledge, this is the first report of seven-, nine-, and eleven-center bonds in crystalline materials.