BaCo₂(AsO₄)₂

Abstract

Key indicators: single-crystal X-ray study; T = 293 K; mean (As-O) = 0.002 Å; R factor = 0.015; wR factor = 0.038; data-to-parameter ratio = 15.5.Suitable single crystals of the title compound, barium dicobalt(II) bis[orthoarsenate(V)], were prepared under hydrothermal conditions. This phase belongs to a series of compounds with general formula AM 2 (XO 4 ) 2 , where A = alkaline earth metal, M = Mg or a divalent first-row transition element, and X = P, As or V. BaCo 2 (AsO 4 ) 2 is isotypic with BaNi 2 (XO 4 ) 2 (X = P, V or As) and is characterized by brucitelike sheets of edge-sharing CoO 6 octahedra (3 symmetry) parallel to (001), with one-third of the octahedral positions being vacant. The sheets are capped above and below by AsO 4 tetrahedra (3 symmetry) and are interconnected by distorted BaO 12 cuboctahedra (3 symmetry). Related literature

Metamagnetic Transitions versus Magnetocrystalline Anisotropy in Two Cobalt Arsenates with 1D Co2+ Chains

“…This metamagnetic behavior is confirmed in M ( H ) curves by the sigmoid shape of the magnetization above 3.2 T at 2 K (see Figure b). The smooth bump of the magnetization and narrow magnetic hysteresis between 3.2 and 6 T is reminiscent of the metamagnetic transition in several Co 2+ -based systems: e.g., CoH 2 P 2 O 7 (chains) and Co 10 Ge 3 O 16 (3D structure) . It corresponds to a spin-flop transition: i.e., the progressive tilting of the spins until total flipping due to relatively “weak” magnetocrystalline anisotropy.…”

“…The corresponding DTA plot shows the two subsequent transformations at 400 and 450 °C (Figure a). HTXRD shows the transformation of 2 into the rhombohedral anhydrous BaCo 2 As 2 O 8 (see Figure b) . During the transformation, the linear edge-sharing chains are rearranged and condensed into honeycomb layers (see section S4, Figure S4b, for the structure); while the 2D character is conserved, Ba 2+ and AsO 4 present similar spacer groups in both the hydrated and anhydrous phases.…”

Magnetic Couplings in Edge-Sharing High-Spin $d^7$ Compounds

“…Real materials span a wide range Co-Co distances in edge-sharing Co(II) compounds, e.g. from ∼ 2.9 Å in BaCo 2 (AsO 4 ) 2 59 to ∼ 3.9 Å in CoI 2 60 . While we leave complete discussion of individual materials for later work, it is useful to establish realistic ranges of hoppings.…”

Magnetic couplings in edge-sharing high-spin d 7 compounds

“…These edge-sharing Co(II) compounds span a wide range Co-Co distances, e.g. from ∼2.9 Å in BaCo 2 (AsO 4 ) 2 [64] to ∼3.9 Å in CoI 2 [68]. For each case, we employed fully relativistic density functional theory calculations performed with FPLO [59,60] at the GGA (PBE [61]) level (as above).…”