Breaking the Zero Dimensional Illusion in Te(IV) Metal Halide Hybrids via Electronic Dimensionality Control.

Zero-dimensional (0D) metal halide hybrids (MHHs) containing ns2 metal ions are attractive solid-state emitters, yet their photoluminescence quantum yields (PLQYs) often vary unpredictably even among structurally similar systems. To identify the factors governing emissivity, we investigate a series of 0D Te(IV)-based hybrids, A2TeCl6 (A+ = BzEt3N+, BzMe2PhN+, Ph4P+, Ph3EtP+), which exhibit nearly identical optical features but display large differences in PLQY and lifetimes. Single-crystal X-ray diffraction, Hirshfeld surface analysis, and Voronoi polyhedral mapping reveal that these variations do not arise from local octahedral distortion but from subtle yet critical deviations in electronic dimensionality dictated by cation-dependent packing. We identify the interoctahedral halide-halide distance as a powerful structural descriptor correlating exciton delocalization and nonradiative quenching. This metric integrates both interoctahedral proximity and orientation effects, outperforming the conventional metric of metal-metal distances. DFT calculations elucidate excited-state relaxation pathways and reproduce the experimental emissivity trend. These results establish a clear structure-property relationship for 0D ns2 metal halide hybrids, offering a predictive framework for designing high-performance luminescent materials.