Boronated cyanometalates ([M(CN-BR₃)₆]^3/4– (M = Cr, Mn, Fe, Ru, Os; R = BPh₃, B(2,4,6,-F₃C₆H₂)₃, and B(C₆F₅)₃(BCF))] have been synthesized and characterized by X-ray crystallography, UV-visible-NIR, NMR, IR, magnetic circular dichroism, elemental analysis, and electronic structure calculations (TDDFT and CASSCF+NEVPT2). The formal potentials for all BCF species anodically shift by 2.08-2.29 V. For dⁿ ≤ d⁵ electronic configurations, ligand-to-metal charge transfer (LMCT) absorptions with simultaneous positive and negative MCD B+C-terms are observed in the spectra of all complexes. CASSCF+NEVPT2 calculations incorporating t_1u and t_2u orbitals accurately reproduce excitation energies for t_1u/t_2u → t_2g transitions. Notably, the formal potentials of the [M(CN-B(C₆F₅)₃)₆]³⁻anions increase with increasing LMCT energies. We report two unique cyanometalates, [Mn(CN-B(C₆F₅)₃)₆]⁵⁻ (a species that is isoelectronic with [Fe(CN-B(C₆F₅)₃)₆]⁴⁻) and [Cr(CN-B(C₆F₅)₃)₆]⁴⁻. Of special interest is that [Mn(CN-B(C₆F₅)₃)₆]⁵⁻ exhibits spin crossover behavior, as evidenced by both low-temperature X-ray crystal structure analysis and ambient temperature spectroscopy.

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Brendon McNicholas

California Institute of Technology

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