Can density functional theory methods accurately compute redox potentials of osmium(II)-polypyridines?

• First benchmark study of osmium(II)–polypyridine redox potentials by DFT. • Born–Haber cycle gives highest accuracy (R² up to 0.99, lowest MAD/RMSD). • Frontier orbital energies provide efficient and reliable predictive correlations. • Direct Gibbs free energy, local-, global descriptors show lower predictive accuracy. • Dual strategy proposed: Born–Haber for benchmarks, orbital energies for screening. This study presents the first systematic computational study of redox potentials of osmium(II)–polypyridine complexes, comparing several density functional theory–based approaches. Using an extended series of 35 complexes, correlations between experimental and calculated potentials were evaluated through the Born–Haber thermodynamic cycle, direct Gibbs free energy calculations, frontier orbital energies, local and global reactivity descriptors. The Born–Haber cycle yielded the highest accuracy (R² up to 0.99, lowest MAD/RMSD), while frontier orbital correlations provided a computationally efficient alternative with only slightly reduced performance. These findings establish a dual strategy: Born–Haber calculations for benchmark accuracy, and orbital-based correlations for rapid screening, thereby providing a robust framework for predicting and rationalizing redox behavior in osmium polypyridine systems.