Realization of heptagonal pyramidal octacoordination in highly robust [OB–M©B7O7]− (M = Co, Rh, Ir) complexes via boron–oxygen synergy

Non-spherical heptagonal pyramidal octacoordination has remained elusive due to extreme repulsion among equatorial ligands. Herein, we computationally demonstrate this unprecedented configuration in monoanionic [OB-M©B7O7]- (M = Co, Rh, Ir) complexes through synergistic integration of an equatorial heptadentate B7O7 ligand and an axial boronyl (-BO) group. Advanced quantum chemical analyses confirm these species as global minima with substantial thermodynamic stability (6.7-7.5 kcal mol-1 below isomers), dynamic integrity up to 1000 K, and exceptional electronic robustness (HOMO-LUMO gaps: 5.12-5.28 eV; VDEs: 3.68-3.79 eV). Critical stabilization arises from (i) B-O σ/π bonding networks compensating equatorial strain, (ii) σ+π+δ triple aromaticity (10σ + 6π + 2δ electrons satisfying Hückel's 4n + 2 rule), and (iii) electrostatic-dominated ligand-metal interactions (56.4%-58.0% attraction per EDA-NOCV). The electron-compensation strategy-using oxygen atoms to electronically compensate electron-deficient boron centers while providing steric protection-enables condensed-phase viability. This work establishes boron-oxygen clusters as versatile platforms for non-classical coordination geometries.