Nb2OsB2, with a New Twofold Superstructure of the U3Si2 Type
The new ternary metal-rich boride, Nb2OsB2, was synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The compound was characterized from single-crystal X-ray data and EDX measurements. It crystalizes as a new superstructure (space group P4/mnc, no. 128) of the tetragonal U3Si2-structure type with lattice parameters a= 5.922(1) Å and c = 6.879(2) Å. All of the B atoms are involved in B2 dumbbells with B![[BOND]](http://onlinelibrarystatic.wiley.com/undisplayable_characters/00f8ff.gif)
B distances of 1.89 (4) Å. Structure relaxation using VASP (Vienna ab intio Simulation Package) has confirmed the space group and the lattice parameters. According to electronic structure calculations (TB-LMTO-ASA), the homoatomic BB interactions are optimized and very strong, but relatively strong heteroatomic OsB, NbB and NbOs bonds are also found: These interactions, which together build a three-dimensional network, are mainly responsible for the structural stability of this new phase.
B distances of 1.89 (4) Å. Structure relaxation using VASP (Vienna ab intio Simulation Package) has confirmed the space group and the lattice parameters. According to electronic structure calculations (TB-LMTO-ASA), the homoatomic BB interactions are optimized and very strong, but relatively strong heteroatomic OsB, NbB and NbOs bonds are also found: These interactions, which together build a three-dimensional network, are mainly responsible for the structural stability of this new phase.All-Boron Planar B6 Ring in the Solid-State Phase Ti7Rh4Ir2B8
Planar B6 rings embedded in one-dimensional Ti7 wheels are found in the crystal structure of a solid-state phase (Ti7Rh4Ir2B8) for the first time. First-principles calculations indicate strong BB bonding but also significant interactions with the surrounding titanium atoms (see picture).
Published as "Hot Paper" in: Angew. Chem. 2012, and Angew. Chem. Int. Ed. 2012. Highlighted in Chemical and Engeneering News (02/2012).
Site-Preferential Design of Itinerant Ferromagnetic Borides
The two phases, MRh6B3 (M = Fe, Co) are isotypic and crystallize in the hexagonal Th7Fe3 structure type (space group P63mc, no. 186, Z = 2). In this structure, the magnetically active atoms (Fe, Co) are preferentially found on only one of the three available rhodium sites, and together with rhodium they build a three-dimensional network of interconnected (Rh/M)3 triangles. Magnetic properties investigations show that both phases order ferromagnetically below Curie temperatures of 240 K (for FeRh6B3) and 150 K (for CoRh6B3). First-principles DFT calculations correctly reproduce not only the lattice parameters but also the ground state magnetic ordering in the two phases. These calculations also show that the long-range magnetic ordering in both phases occurs via indirect ferromagnetic coupling between the iron atoms mediated by rhodium.
Published in: Inorg.Chem. 2011, DOI: 10.1021/ic2013655.
Ferrimagnetism induced by scaffolding: A DFT Analysis
Through a combination of calculations on specific models and using the rigid band approximation, which is validated by the DOS curves for “Ti9-nFe2+nRu18B8” (n = 0, 0.5, 1, 2, 3), mixing of Fe and Ti is anticipated at both the 2b- and 4h-chain sites. The model “Ti8.5Fe2.5Ru18B8” (n = 0.5) revealed that both Brewer-type Ti−Ru interactions as well as ligand field splitting of the Fe 3d orbitals regulated the observed valence electron counts between 220 and 228 electrons/formula unit. Finally, models of magnetic structures were created using “Ti6Fe5Ru18B8” (n = 3). A rigid band analysis of the LSDA DOS curves concluded preferred ferromagnetic ordering at low Fe content (n ≤ 0.75) and ferrimagnetic ordering at higher Fe content (n > 0.75). Ferrimagnetism arises from antiferromagnetic exchange coupling in the scaffold of Fe1-ladder and 4h-chain sites.
Published in: J. Am. Chem. Soc. 2011, DOI: 10.1021/ja200909r
