Peierls-distorted monoclinic MnB4 with a mn-Mn 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 MnB4 have now been grown. The compound crystallizes in the monoclinic crystal system (space group P2 1/c) with a structure that has four crystallographically independent boron-atom positions, as confirmed by 11B 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 MnI 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 MnB4. Now available as crystals: The structure of single crystals of MnB4 (see picture) was solved using group-subgroup relationships and showed an unexpected short Mn-Mn bond caused by Peierls distortion. Calculations indicate MnI centers and paramagnetism, as confirmed by magnetic measurements. The tetraboride exhibits a pseudo-band gap and semiconducting behavior. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.