Peierls‐Distorted Monoclinic MnB4with a MnMn Bond

Abstract Tetraborides of chromium and manganese exhibit an unusual boron‐atom framework that resembles the hypothetical tetragonal diamond. They are believed to be very hard. Single crystals of MnB 4 have now been grown. The compound crystallizes in the monoclinic crystal system (space group P 2 1 / c ) with a structure that has four crystallographically independent boron‐atom positions, as confirmed by 11 B MAS‐NMR spectroscopy. An unexpected short distance between the Mn atoms suggests a double Mn–Mn bond and is caused by Peierls distortion. The structure was solved using group‐subgroup‐relationships. DFT calculations indicate Mn I centers and paramagnetism, as confirmed by magnetic measurements. The density of states shows a pseudo‐band gap at the Fermi energy and semiconducting behavior was observed for MnB 4 .