title: A Radical Tricationic Rhomboid Tetraborane(4) with Four-Center, Five-Electron Bonding.
abstract: The red-colored tetraborane(4) [B4 (hpp)4 ](3+.) (3; hpp=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinate) with a rhomboid B4 skeleton stabilized by four N donors, was synthesized by the reaction of the strong hydride abstraction reagent [(acridine)BCl2 ][AlCl4 ] with the electron-rich diborane(4) [HB(hpp)]2 (1). The salt 3[AlCl4 ]3 was structurally characterized and the presence of unpaired electrons proven by EPR measurements. The unprecedented radical tricationic 3 is distinguished by a high positive charge and boron atoms in a low oxidation state (less than two).
authors.affiliation: Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Litters
authors.affiliation: Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Kaifer
authors.affiliation: Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany. hans-jorg.himmel@aci.uni-heidelberg.de.
authors.forename: Hans-Jörg
authors.initials: HJ
authors.lastname: Himmel
keywords: boron; hydride abstraction; multiple-center bonding; radicals