Hydrogen‐Bond‐Mediated Modulation of the Valence Band in Isostructural Morpholinium‐Based Bi ³⁺ and Sb ³⁺ Iodides

Two isostructural zero‐dimensional (0D) hybrid metal iodides, (MOR) ₂ (H ₅ O ₂ )[BiI ₆ ] ( 1 ) and (MOR) ₂ (H ₅ O ₂ )[SbI ₆ ] ( 2 ) (MOR = morpholinium), were synthesized and characterized. Single‐crystal X‐ray diffraction at 100 K reveals isolated [BiI ₆ ] ³⁻ and [SbI ₆ ] ³⁻ octahedra separated by morpholinium cations and Zundel‐like (H ₅ O ₂ ) ⁺ units forming an extended hydrogen‐bonding network. Hirshfeld surface analysis confirms the complementary roles of strong O─H ··· O hydrogen bonds and weaker H···I contacts in stabilizing this framework. DFT calculations including spin–orbit coupling show that optical absorption is dominated by the inorganic framework. Remarkably, interaction between (H ₅ O ₂ ) ⁺ and [BiI ₆ ] ³⁻ modifies the composition of the valence band maximum, whereas no analogous effect is observed in 2 containing [SbI ₆ ] ³⁻ octahedra. Diffuse reflectance measurements confirm calculated bandgaps and reveal different transition characters for both materials demonstrating that subtle hydrogen‐bond‐mediated electronic interactions can govern the electronic structure of structurally analogous 0D hybrid halides. Both compounds exhibit reversible thermochromism upon cooling (amber‐orange → pale yellow for 1 and golden yellow → pale greenish‐yellow for 2 ); additionally, 1 generates green luminescence attributed to the ³ P ₁  →  ¹ S ₀ transition whereas 2 displays red to NIR photoluminescence attributed to both singlet and triplet self‐trapped excitons (STE).