Ligand Electronics Dictate Geometry, Stability, and Cancer Cell Toxicity in Carbon‐Stabilized Gold(III) Macrocycles

) and electronically tuned cyclometalated [C^N] templates. Systematic installation of substituents that modulate σ-donation to Au(III) produces predictable shifts in Au-C and Au-P bond lengths, trans bite angles, and square planar deformation. σ-donor character of complexes influences geometric distortion, aqueous stability, and up to an order-of-magnitude higher cytotoxicity in triple-negative breast cancer and estrogen receptor-positive models compared to cisplatin. Mechanism of action studies supports acute mitochondrial uncoupling and mtROS production, leading to cell death by this class of compounds. This electronic-structural-biological correlation provides a rare, experimentally validated design principle for Au(III) scaffolds and positions electronically tuned macrocycles as a chemically tractable platform for targeting intracellular pathways.