posted on 2022-12-19, 14:37authored byBrendon J. McNicholas, Cherish Nie, Anex Jose, Paul H. Oyala, Michael K. Takase, Larry M. Henling, Alexandra T. Barth, Alessio Amaolo, Ryan G. Hadt, Edward I. Solomon, Jay R. Winkler, Harry B. Gray, Emmanuelle Despagnet-Ayoub
Thirteen boronated cyanometallates [M(CN-BR3)6]3/4/5– [M = Cr, Mn, Fe, Ru, Os; BR3 = BPh3, B(2,4,6,-F3C6H2)3, B(C6F5)3]
and one
metalloboratonitrile [Cr(NC-BPh3)6]3– have been characterized by X-ray crystallography and spectroscopy
[UV–vis–near-IR, NMR, IR, spectroelectrochemistry, and
magnetic circular dichroism (MCD)]; CASSCF+NEVPT2 methods were employed
in calculations of electronic structures. For (t2g)5 electronic configurations, the lowest-energy ligand-to-metal
charge-transfer (LMCT) absorptions and MCD C-terms
in the spectra of boronated species have been assigned to transitions
from cyanide π + B–C borane σ orbitals. CASSCF+NEVPT2
calculations including t1u and t2u orbitals
reproduced t1u/t2u → t2g excitation
energies. Many [M(CN-BR3)6]3/4– complexes exhibited highly electrochemically reversible redox couples.
Notably, the reduction formal potentials of all five [M(CN-B(C6F5)3)6]3– anions scale with the LMCT energies, and Mn(I) and Cr(II) compounds,
[K(18-crown-6)]5[Mn(CN-B(C6F5)3)6] and [K(18-crown-6)]4[Cr(CN-B(C6F5)3)6], are surprisingly
stable. Continuous-wave and pulsed electron paramagnetic resonance
(EPR; hyperfine sublevel correlation) spectra were collected for all
Cr(III) complexes; as expected, 14N hyperfine splittings
are greater for (Ph4As)3[Cr(NC-BPh3)6] than for (Ph4As)3[Cr(CN-BPh3)6].