Paramagnetic Semiconducting Se-Mn Clusters: A Mn 3 Se 4 -Stabilized Selenide Radical Intermediate and Its Aggregated Derivatives

The transition metal-stabilized heavy main group radicals are extremely scarce due to their highly reactive natures, making them difficult to be isolated and identified. We report here a rare class of the Se radical-containing manganese carbonyl anionic cluster, [(μ-Se)(μ -Se ) Mn (CO) ] ( ), which was successfully obtained from the one-pot reaction of Se powder and Mn (CO) in concentrated KOH/MeOH/MeCN solutions at 90 °C. Dianion and its dimeric cluster, [(μ -Se ){(μ -Se ) Mn (CO) } ] [ ], could undergo the reversible Se-Se bond breakage or reformation by the thermal cracking of or self-dimerization of , showing the μ-Se radical character of . Complex could react with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) to form the Se radical-captured complex [(μ-Se(TEMPO)) (μ -Se ) Mn (CO) ] ( ) or could react with alkylene bromides (CH ) Br ( = 1, 2) to give the Mn -based oxidative coupling products, [(μ -Se )(μ-Se LSe) Mn (CO) ] (L = CH , ; Se, ). In addition, dianion and its aggregated derivatives , , , and exhibited unusual paramagnetic properties with the spin-state switching from = 1 (Mn) + 1/2 (Se) to = 1 (Mn), in which their magnetic centers were proved to be mixed-valent Mn atoms and the μ-Se radical, as evidenced by Evans method, superconducting quantum interference device, X-ray photoelectron spectra, electron paramagnetic resonance, and density functional theory calculations. Importantly, these clusters showed semiconducting behaviors with low and tunable energy gaps (1.50-2.01 eV) and varied electrical conductivities (2.52 × 10 -4.58 × 10 S/cm), where efficient electron transports mainly arose from C-H(phenyl)···O(carbonyl) interactions within the solid-state frameworks.