TM₇TM′₆B₈(TM= Ta, Nb;TM′ = Ru, Rh, Ir): New Compounds with [B₆] Ring Polyanions

Abstract

The ternary boron compounds TM(7)TM'(6)B(8) (TM = Ta, Nb; TM' = Ru, Rh, Ir) were prepared by high-temperature thermal treatment of mixtures of the elements. An analysis of the chemical bonding by the electron density/electron localizability approach reveals formation of covalently bonded polyanions [B(6)] and [TM'(6)B(2)]. The cationic part of the structure contains separated TM cations. In agreement with the chemical bonding analysis and band structure calculations, all TM(7)TM'(6)B(8) compounds are metallic Pauli-paramagnets (TM' = Ru, Rh) or diamagnets (TM' = Ir).

Structural‐Distortion‐Driven Magnetic Transformation from Ferro‐ to Ferrimagnetic Iron Chains in B6‐based Nb6FeIr6B8

“…Refinement of the neutron data using the substructure led to R values that were nearly twice as large.C onsequently,t he annealed compound crystallizes with the proposed new superstructure model ( Figure 1). [13] Ther efined lattice parameters at 6K are a = 16.0821(2) and c = 6.5983 (2) ,and as expected, adecrease in the lattice parameters was observed with decreasing temperature from 500 to 6K (see Table S1 and inset of Figure S2). [13] Ther efined lattice parameters at 6K are a = 16.0821(2) and c = 6.5983 (2) ,and as expected, adecrease in the lattice parameters was observed with decreasing temperature from 500 to 6K (see Table S1 and inset of Figure S2).…”

“…

We report on as tructural distortion of kinetically stable B 6 -based ferromagnetic Nb 6 FeIr 6 B 8 that induces an unprecedented transformation of aferromagnetic Fe chain into two ferrimagnetic Fe chains through superstructure formation. [4] One such arrangement is the planar B 6 ring, first reported in the compound Ti 7 Rh 4 Ir 2 B 8 [12] and later found in several other phases,such as M 7 T 6 B 8 (M = Nb,T a; T= Ru, Rh, Ir), [13] Nb 6 Fe 1Àx Ir 6+x B 8 , [14] and M 7 Fe 3 B 8 (M = Nb,T a). This finding paves the way for the development of lowdimensional magnetic intermetallic systems based on Heisenberg ferrimagnetic chains,which have previously been studied only in molecular-based compounds.

Transition-metal-rich borides form an interesting class of compounds with aw ide range of crystal structures and interesting physical properties.

…”

Unexpected Synergy between Magnetic Iron Chains and Stacked B6 Rings in Nb6Fe1−xIr6+xB8

“…[9][10][11] In the crystal structure of these phases, boron atoms are isolated from each other and they do not interact with the 3d transition metals (including the magnetically active element) too. A different situation is found in the recently discovered Ti 7 Rh 4 Ir 2 B 8 and M 7 T 6 B 8 (M = Nb, Ta; T = Ru, Rh, Ir) phases, [14] in which the titanium, niobium, and tantalum chains strongly interact with the B 6 rings. Therefore, inducing long-range magnetic order in these phases, by substituting non-magnetic chains by chains of magnetically active elements is not granted, because of the possible strong bonding interactions of these magnetic chains with the B 6 rings.…”

“…Of all ternary M 7 T 6 B 8 phases, those with T = Ir have been reported to be difficult to synthesize and no single crystals could be obtained. [14] Consequently, the thermodynamically less-stable quaternary Ir-based phase should be even more difficult to synthesize under the same conditions. Indeed, only about 12 % of the expected phase was obtained when applying the same synthetic procedure reported for the ternary phase.…”

Hierarchical and chemical space partitioning in new intermetallic borides MNi21B20(M = In, Sn)

“…3,11,12 Two-dimensional boron networks in turn can be often observed at intermediate metal-to-boron ratios between 3/2 and 2, 3,13,14 whereas, with decreasing boron content, separated chains or rings and, further, isolated boron atoms prevail. [15][16][17][18][19] Therefore, studying the phase diagram at intermediate compositions enables one to follow the structural evolution of and bonding interactions between boron aggregates and metal framework observed in complex intermetallic compounds. The recently discovered compounds MNi 9 B 8 (M = Al, Ga) 20 represent this structural complexity in an instructive way.…”