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Crystal structure of Ba₂Co(BO₃)₂.

ABSTRACT: Single crystals of dibarium cobalt(II) bis-(orthoborate), Ba₂Co(BO₃)₂, have been obtained from the melt. The crystal structure is composed of two isolated (BO₃)^3- triangles linked to Co²⁺ cations. The resulting [CoO₅] square pyramids and the borate anions make up branched rows extending parallel to [010]. The barium cations occupy two sites in the voids of this arrangement and exhibit coordination numbers of nine each. A comparison with the structures of other A ₂ M(BO₃)₂ compounds reveals a unique five-coordination of the small metal M in the title compound instead of four- or six-coordination for the other A ₂ M(BO₃)₂ compounds with M = Cu, Zn, Mg, Ca, or Cd.

SUBMITTER: N'Faoui FE

PROVIDER: S-EPMC6399684 | biostudies-literature | 2019 Mar

REPOSITORIES: biostudies-literature

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Crystal structure of Ba2Co(BO3)2.

N'Faoui Fatima-Ezahra FE Aride Jilali J Boukhari Ali A Taibi M'Hamed M Saadi Mohamed M El Ammari Lahcen L

Acta crystallographica. Section E, Crystallographic communications 20190222 Pt 3

Single crystals of dibarium cobalt(II) bis-(orthoborate), Ba2Co(BO3)2, have been obtained from the melt. The crystal structure is composed of two isolated (BO3)3- triangles linked to Co2+ cations. The resulting [CoO5] square pyramids and the borate anions make up branched rows extending parallel to [010]. The barium cations occupy two sites in the voids of this arrangement and exhibit coordination numbers of nine each. ...[more]

PMID: 30867955

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Project description:The cobalt carbonate hydroxide Co2CO3(OH)2 is a technologically important solid which is used as a precursor for the synthesis of cobalt oxides in a wide range of applications. It also has relevance as a potential immobilizer of the toxic element cobalt in the natural environment, but its detailed crystal structure is so far unknown. The structure of Co2CO3(OH)2 has now been investigated using density functional theory (DFT) simulations and powder X-ray diffraction (PXRD) measurements on samples synthesized via deposition from aqueous solution. Two possible monoclinic phases are considered, with closely related but symmetrically different crystal structures, based on those of the minerals malachite [Cu2CO3(OH)2] and rosasite [Cu1.5Zn0.5CO3(OH)2], as well as an orthorhombic phase that can be seen as a common parent structure for the two monoclinic phases, and a triclinic phase with the structure of the mineral kolwezite [Cu1.34Co0.66CO3(OH)2]. The DFT simulations predict that the rosasite-like and malachite-like phases are two different local minima of the potential energy landscape for Co2CO3(OH)2 and are practically degenerate in energy, while the orthorhombic and triclinic structures are unstable and experience barrierless transformations to the malachite phase upon relaxation. The best fit to the PXRD data is obtained using a rosasite model [monoclinic with space group P1121/n and cell parameters a = 3.1408?(4)?Å, b = 12.2914?(17)?Å, c = 9.3311?(16)?Å and ? = 82.299?(16)°]. However, some features of the PXRD pattern are still not well accounted for by this refinement and the residual parameters are relatively poor. The relationship between the rosasite and malachite phases of Co2CO3(OH)2 is discussed and it is shown that they can be seen as polytypes. Based on the similar calculated stabilities of these two polytypes, it is speculated that some level of stacking disorder could account for the poor fit of the PXRD data. The possibility that Co2CO3(OH)2 could crystallize, under different growth conditions, as either rosasite or malachite, or even as a stacking-disordered phase intermediate between the two, requires further investigation.

Dataset Information

Crystal structure of Ba₂Co(BO₃)₂.

Publications

Crystal structure of Ba<sub>2</sub>Co(BO<sub>3</sub>)<sub>2</sub>.

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