Structure and Chemical Bonding in Medium-Size Boron ClustersDoped with Praseodymium br

:after reports of unusually low oxidation states of lanthanideelements in Ln-B clusters and their inverse sandwich geometrical topologies, theinterest shifted from boride clusters doped with transition metal (TM) elements tothe boride clusters doped with lanthanide atoms. In this work, the results obtainedby a combined approach consisting of CALYPSO structure predictions and densityfunctional theory (DFT) calculations for the neutral and anionic PrBnseries,n=7-16, are reported. A close agreement between our calculated vertical detachmentenergies and experimental data supports the accuracy of the results obtained.Contrary to the medium-size TM-doped medium boron clusters, which preferthree types of structural configurations, all lowest-energy states of the medium-sizePr-doped boron clusters have half-sandwich geometries. An interesting structuralevolution pattern was found for both neutral and anionic PrBnclusters atn= 7, 10, 13, and 16, which includes quasi-planar B7unitshalf-sandwiching the Pr atom. Unusual oxidation numbers of +2 and +1 were found for the Pr atom in the PrB7-and PrB8-anions,respectively. Chemical bonding analysis for the neutral PrB7and PrB13clusters revealed that their high stability stems frominteractions between Pr 5d and B 2p orbitals. A stable tubular-shaped PrB30cluster is proposed as a promising building block forboron-based nanotubes.