Stabilization of Sb₄ Tetrahedra in Paramagnetic Transition Metal Carbonyl Complexes

We present a straightforward synthetic route to the novel chromium carbonyl-stabilized paramagnetic Sb₄-based cluster [Et₄N]₄[Sb₄Cr₆(CO)₂₈] ([Et₄N]₄[1]), which represented a rare example of the intact Sb₄ tetrahedron structurally characterized in the solid state. Complex 1 exhibited versatile reactivities toward groups 7-9 metal carbonyls, dioxygen, or [Cu(MeCN)₄][BF₄] to form selective orbital-controlled Sb₄-based products, including transmetalated paramagnetic complexes [Et₄N]₄[Sb₄Cr₅Mn(CO)₂₈]Br ([Et₄N]₄[1-Mn]Br), [Et₄N]₄[Sb₄Cr₂Fe₆(CO)₃₀] ([Et₄N]₄[1-Fe]), and [Et₄N]₂[Sb₄Cr₄Co₄(CO)₃₁] ([Et₄N]₂[1-Co]), the dioxygen-activated paramagnetic cluster [Et₄N]₄[O₂Sb₄Cr₆(CO)₂₈] ([Et₄N]₄[1-O₂]), or the spin-quenched complex [Et₄N]₂[Sb₄Cr₆(CO)₂₈] ([Et₄N]₂[2]), respectively. The structural nature, bonding properties, paramagnetism, and semiconductivity of these unprecedented transition metal carbonyl-protected Sb₄-based clusters were further realized with DFT calculations.