Mg8Rh4B -: A new type of boron stabilized Ti2Ni structure

The new magnesium rhodium boron compound Mg8Rh4B has been synthesized by reaction of the metal powders with crystalline or amorphous boron or the RhB precursor. The crystal structure Of Mg8Rh4B was solved using single-crystal X-ray diffraction data (space group Fd (3) over barm, a = 12.1711(4) angstrom, Z = 8,174 reflections, R-F = 0.016). The crystal structure can be described as a filled Ti2Ni type where the interstitial sites 8b (1/2, 1/2, 1/2) located at the center of two nested Mg4Rh4 tetrahedra, are occupied by boron atoms. Taking into account the absence of the Ti2Ni-type phase in the binary Mg-Rh system, the boron atoms can be considered as stabilizing this structural motif. From the bonding analysis with the electron localization function the crystal structure is described as covalently bonded [Rh4B](3-) anions, embedded in a cationic magnesium matrix. (c) 2005 Elsevier Inc. All rights reserved.