Fig. 3: X-ray solid-state structures of the CBP–NHC precursors and their corresponding carbon-centered radicals.

a X-ray solid-state structures for precursor 2a and radical 4a. b X-ray solid-state structures for precursor 2b and radical 4b. c X-ray solid-state structures for precursor 2c and radical 4c. θ: the twisted angle between the C3–C2–C4 and N1–C1–N2 plane. The single crystals of radical precursors 2a–c were grown by slowly diffusing diethyl ether into a saturated acetonitrile solution at ambient temperature. The single crystals of radicals 4a–c can be obtained from a saturated hexane solution after cooling to −30 °C. Thermal ellipsoids are shown with 50% probability. Color scheme: C, gray; N, blue. Hydrogen atoms, the counter anion, and solvent molecules are omitted for clarity. Selected bond lengths and angles Å and deg: (2a): C1–N1 1.347(3); C1–N2 1.351(3); <N1–C1–N2 107.3(2). (2b): C1–N1 1.340(3); C1–N2 1.349(3); <N1–C1–N2 107.2(2). (2c): C1–N1 1.325(3); C1–N2 1.332(3); <N1–C1–N2 112.08(18). (4a): C1–N1 1.399(2); C1–N2 1.399(2); <N1–C1–N2 103.1(2). (4b): C1–N1 1.400(2); C1–N2 1.404(2); <N1–C1–N2 103.87(14). (4c): C1–N1 1.382(5); C1–N2 1.389(4); <N1–C1–N2 108.5(3).