(C₆H₆Cr)_n&B₄₀ (n = 1–6): Exohedral Borospherene Complexes with Cage-like B₄₀ as an Effective Ligand with Multiple Coordination Sites

Abstract

The newly discovered cage-like borospherene D_2d B₄₀ with two η⁶-B₆ hexagons and four η⁷-B₇ heptagons on the surface may serve as an effective multi-dentate ligand to coordinate transition metals. Based upon extensive density functional theory calculations, we present herein the possibility of the exohedral complex series (C₆H₆Cr)_n&B₄₀ (n = 1–6) with n Cr centres sandwiched between the central η^6/7-B₄₀ unit and n planar η⁶-C₆H₆ ligands. C₆H₆Cr fragments in (C₆H₆Cr)_n&B₄₀ occupy the η⁶-B₆ hexagonal coordination site atop the B₄₀ cage first, the four neighboring η⁷-B₇ heptagons on the waist next, and finally the η⁶-B₆ hexagon at the bottom, forming a multinuclear complex series effectively stabilized by n C₆H₆Cr fragments. The two η⁶-B₆ hexagons and four η⁷-B₇ heptagons on the spherical surface of B₄₀ can be practically viewed as six independent coordination sites to coordinate Cr centers with almost the same coordination energies. Detailed bonding analyses indicate that the eclipsed C_2v C₆H₆Cr&B₄₀ (1-1) possesses a coordination bonding pattern similar to that of dibenzenechromium, with the B₄₀ ligand inheriting the σ + π double delocalization bonding pattern of the parent borospherene. The IR, Raman, and UV–vis absorption spectra of C_2v C₆H₆Cr&B₄₀ (1-1) are theoretically simulated to facilitate its future experimental characterization.