ScRu 2 B 3 and Sc 2 RuB 6 : Borides Featuring a 2D Infinite Boron Clustering.

Two borides, ScRu2 B3 and Sc2 RuB6 , were obtained by argon-arc melting of the elements followed by annealing at 800 °C. ScRu2 B3 exhibits a new structure type with the space group Cmcm (a = 3.0195(2) Å, b = 15.4056(8) Å, c = 5.4492(3) Å; single crystal X-ray data; RF 2 = 0.0105). Sc2 RuB6 adopts the Y2 ReB6 -type structure (space group Pbam; a = 8.8545(2) Å, b = 11.1620(3) Å, c = 3.4760(1) Å; single crystal X-ray data; RF 2 = 0.0185). ScRu2 B3 displays an unusual intergrowth of CeCo3 B2 - and AlB2 -related slabs; a striking feature is a boat configuration of puckered boron hexagons within infinite graphite like boron layers (63 nets). Sc2 RuB6 presents two-dimensional planar nets of condensed boron pentagons, hexagons, and heptagons sandwiched between metal layers. In Sc/Y substituted Y2 ReB6 -type, Y atoms are distributed exclusively inside the boron heptagons. Exploration of the Sc-Ru-B system at 800 °C including binary boundaries employing EPMA and powder X-ray diffraction technique furthermore rules out the existence of previously reported "ScRuB4 " but confirms the formation and crystal structure of Sc2 Ru5 B4 . ScRu4 B4 forms in cast alloys (LuRu4 B4 -type structure; space group I41 /acd (No. 142), a = 7.3543(2) Å, c = 14.92137(8) Å). Cell parameters and atomic coordinates have been refined for ScRu2 B3 , Sc2 RuB6 , and ScRu4 B4 in the scope of the generalized gradient approximation. Ab initio electronic structure calculations indicate a moderate electronic density of states at the Fermi level situated near the upper edge of essentially filled d-bands. Electrical resistivity measurements characterize ScRu2 B3 and Sc2 RuB6 as metals in concord with electronic band structure calculations.