Antimony Dopant-Driven Monomer–Dimer Structural Transition in a Zero-Dimensional Indium Halide Hybrid

While metal-ion doping is typically known to preserve the structural and dimensional integrity of zero-dimensional (0D) host metal halide hybrids, introducing only subtle local perturbations, this work uncovers a striking deviation from this paradigm. We demonstrate that dopant incorporation can serve as an effective overall structural modulator, inducing transformations in coordination geometry and framework connectivity/dimensionality. Specifically, Sb 3+ ions act as dopants that drive a transition in a 1-methylpiperazine-based indium bromide hybrid ((C 5 H 14 N 2 ) 2 InBr 7 ·H 2 O) from a monomeric 0D structure with isolated [InBr 6 ] 3– octahedral units to a dimeric framework ((C 5 H 14 N 2 ) 2 In 1.81 Sb 0.19 Br 10 ·(H 2 O) 2 ) featuring edge-sharing [(In/Sb) 2 Br 10 ] 4– octahedral units that exhibit strong orange emission (photoluminescence quantum yield of ≈59%). The structural modulation persists across a broad Sb 3+ concentration range and mirrors the dimeric nature of the Sb analogue control sample ((C 5 H 14 N 2 ) 2 Sb 2 Br 10 ·(H 2 O) 2 ). DFT and thermodynamic formation energy analyses confirm self-trapped exciton-mediated Sb 3+ emission and the energetic preference for the dimeric phase, establishing doping as a powerful route for tuning the overall structure/dimensionality and luminescence of 0D metal halide hybrids.