Bandgap modification in 0D tellurium iodide perovskite derivatives via incorporation of polyiodide species

Halide perovskites provide a versatile platform for exploring the effect of non-covalent interactions, including halogen bonding, on material properties such as band gap, luminescence, and frontier orbital landscape. Herein we report six new zero-dimensional tellurium iodide perovskite derivatives, consisting of [TeI(6)](2−) octahedra charge balanced by one of several X-Py cations (X = H, Cl, Br, I, and Py = pyridinium). These compounds also feature robust halogen bonding between [TeI(6)](2−) octahedra and polyiodides in the form of I(2) (1–4), I(3)(−) (5), or adjacent octahedra (4 and 6). These relatively strong non-covalent interactions (NCIs) are modeled by natural bond order (NBO) and second order perturbation theory (SOPT) calculations. NCIs are responsible for reducing the bandgap of these materials (measured via diffuse reflectance spectroscopy) relative to those without polyiodide species. They also affect inner sphere bonding in the metal halide, exacerbating [TeI(6)](2−) octahedron asymmetry as compared to previously published compounds, with greater asymmetry correlating with higher van der Waals overlap of halogen–halogen contacts. We also demonstrate the ability of hydrogen and carbon bonding (which dominates in the absence of polyiodides) to affect inner sphere tellurium iodide bonding and octahedral symmetry.