Impact of noncovalent interactions on structural and photophysical properties of zero-dimensional tellurium(iv) perovskites

Reported is the synthesis and characterization of eight new halotellurate(iv) compounds consisting of isolated [TeX6](2-) (X = Cl, Br) octahedra charge balanced by halopyridinium (XPy; X = H, Cl, Br, I) cations and assembled via non-covalent interactions (NCIs) in the second coordination sphere. Computational density functional theory (DFT) based natural bonding orbital (NBO) and density of state (DOS) methods were utilized to (i) map the band structure, (ii) quantify and categorize noncovalent interaction strength and type, and (iii) deconstruct metal-halide bonding orbitals. Our findings demonstrate the influence of NCIs on Te-X bonding, particularly atomic orbital hybridization, and the ability to tune band gap energies as a function of noncovalent interaction type and strength. In brief, band gap energies for the [TeCl6](2-) materials are shown to decrease with increasing NCI strength, whereas the opposite is true for [TeBr6](2-) compounds. This report is a useful platform for probing the relationship between second sphere effects and the structural and photophysical properties within the halotellurate(iv) family of low dimensional perovskites.