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Crystal structure of BaMnB 2 O 5 containing structurally isolated manganese oxide sheets

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ABSTRACT

In an attempt to search for mixed alkaline-earth and transition metal pyroborates, the title compound, barium manganese(II) pyroborate, has been synthesized by employing a flux method. The structure of BaMnB2O5 is composed of MnO5 square pyramids that form Mn2O8 dimers by edge-sharing and of pyroborate units ([B2O5]4−) that are composed of two corner-sharing trigonal–planar BO3 units. These building blocks share corners to form ∞2[MnB2O5]2− layers extending parallel to (100). The Ba2+ cations reside in the gap between two manganese pyroborate slabs with a coordination number of nine. The title compound forms an inter­esting spiral framework propagating along the 21 screw axis. The structure is characterized by two alternating layers, which is relatively rare among known transition-metal-based pyroborate compounds.

No MeSH data available.


(a) The Mn1O5 square pyramids (ball and stick drawing) share a common edge, O2—O2, forming an Mn2O8 unit. (b) The B2O3 unit (polyhedral drawing), shares two corners with neighboring MnO5 square pyramids (ball and stick drawing) through O1 and O2. The only unshared oxygen, O4, of the pyroborate group forms a bond with a Ba atom.
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fig3: (a) The Mn1O5 square pyramids (ball and stick drawing) share a common edge, O2—O2, forming an Mn2O8 unit. (b) The B2O3 unit (polyhedral drawing), shares two corners with neighboring MnO5 square pyramids (ball and stick drawing) through O1 and O2. The only unshared oxygen, O4, of the pyroborate group forms a bond with a Ba atom.

Mentions: There is one crystallographically independent Mn atom which is coordinated by five oxygen atoms to form a square pyramid with four longer equatorial Mn—O bonds and one short apical Mn—O bond. Fig. 2 ▸a shows two Mn1O5 square pyramids sharing a common edge, O2—O2(−x + 1, −y, −z), to form an Mn2O8 unit. As shown in Fig. 3 ▸a, Mn atoms are connected to each other via oxygen atoms with a Mn1⋯Mn1 separation of 3.317 (2) Å and an Mn1—O2—Mn1 angle of 101.23 (16)°. The neighboring Mn2O8 dimers share vertices through oxygen atom O3. The oxygen atom O1 in the Mn2O8 dimer is only corner-shared by the pyroborate group. The only unshared oxygen, O4, of the pyroborate group is pointing into the free space towards the neighboring slabs to form a bond with the barium atom. As shown in Fig. 3 ▸b, with respect to the pyroborate group, the B2O3 unit shares two corners with neighboring MnO5 square pyramids through O1 and O2 while the B1O3 unit corner-shares a common oxygen atom, O3, with two other MnO5 square pyramids. This arrangement facilitates the observed curvature which is necessary for the spiral framework found in the extended lattice (Fig. 1 ▸b). The unique arrangement of B2O5 groups around the 21 screw axis provides an essential element allowing the spiral chain to propagate along the b axis. It is well known that the inter­planar angle of the B2O5 group is primarily dictated by packing effects and the nature of the associated cations in the given structure (Thompson et al., 1991 ▸). In addition to that, as previously noted, the greater deviations from coplanarity are observed in the arrangement of the B2O5 groups due to variation of the sizes of alkali metals in alkali metal Nb and Ta oxide pyroborates (Akella & Keszler, 1995 ▸). Accordingly, the inter-planar angle of the B2O5 group is likely to be determined by the associate coordination environment of the barium cations in the title compound. It should be noted that the connectivity of the Mn2O8 and B2O5 structure units would result in a ‘dangling’ framework unless it can be tightly held together by external bonds. The Ba2+ cations, in this case, reside in the spiral framework arranging in zigzag fashion to support and maintain the distance between neighboring [MnB2O5]2− slabs. Coincidentally, this wavy arrangement is critical for the spiral chain to propagate along the b axis. The flexible [MnB2O5]2− framework revolves around Ba2+ cations, suggesting a template-like behavior.


Crystal structure of BaMnB 2 O 5 containing structurally isolated manganese oxide sheets
(a) The Mn1O5 square pyramids (ball and stick drawing) share a common edge, O2—O2, forming an Mn2O8 unit. (b) The B2O3 unit (polyhedral drawing), shares two corners with neighboring MnO5 square pyramids (ball and stick drawing) through O1 and O2. The only unshared oxygen, O4, of the pyroborate group forms a bond with a Ba atom.
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fig3: (a) The Mn1O5 square pyramids (ball and stick drawing) share a common edge, O2—O2, forming an Mn2O8 unit. (b) The B2O3 unit (polyhedral drawing), shares two corners with neighboring MnO5 square pyramids (ball and stick drawing) through O1 and O2. The only unshared oxygen, O4, of the pyroborate group forms a bond with a Ba atom.
Mentions: There is one crystallographically independent Mn atom which is coordinated by five oxygen atoms to form a square pyramid with four longer equatorial Mn—O bonds and one short apical Mn—O bond. Fig. 2 ▸a shows two Mn1O5 square pyramids sharing a common edge, O2—O2(−x + 1, −y, −z), to form an Mn2O8 unit. As shown in Fig. 3 ▸a, Mn atoms are connected to each other via oxygen atoms with a Mn1⋯Mn1 separation of 3.317 (2) Å and an Mn1—O2—Mn1 angle of 101.23 (16)°. The neighboring Mn2O8 dimers share vertices through oxygen atom O3. The oxygen atom O1 in the Mn2O8 dimer is only corner-shared by the pyroborate group. The only unshared oxygen, O4, of the pyroborate group is pointing into the free space towards the neighboring slabs to form a bond with the barium atom. As shown in Fig. 3 ▸b, with respect to the pyroborate group, the B2O3 unit shares two corners with neighboring MnO5 square pyramids through O1 and O2 while the B1O3 unit corner-shares a common oxygen atom, O3, with two other MnO5 square pyramids. This arrangement facilitates the observed curvature which is necessary for the spiral framework found in the extended lattice (Fig. 1 ▸b). The unique arrangement of B2O5 groups around the 21 screw axis provides an essential element allowing the spiral chain to propagate along the b axis. It is well known that the inter­planar angle of the B2O5 group is primarily dictated by packing effects and the nature of the associated cations in the given structure (Thompson et al., 1991 ▸). In addition to that, as previously noted, the greater deviations from coplanarity are observed in the arrangement of the B2O5 groups due to variation of the sizes of alkali metals in alkali metal Nb and Ta oxide pyroborates (Akella & Keszler, 1995 ▸). Accordingly, the inter-planar angle of the B2O5 group is likely to be determined by the associate coordination environment of the barium cations in the title compound. It should be noted that the connectivity of the Mn2O8 and B2O5 structure units would result in a ‘dangling’ framework unless it can be tightly held together by external bonds. The Ba2+ cations, in this case, reside in the spiral framework arranging in zigzag fashion to support and maintain the distance between neighboring [MnB2O5]2− slabs. Coincidentally, this wavy arrangement is critical for the spiral chain to propagate along the b axis. The flexible [MnB2O5]2− framework revolves around Ba2+ cations, suggesting a template-like behavior.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

In an attempt to search for mixed alkaline-earth and transition metal pyroborates, the title compound, barium manganese(II) pyroborate, has been synthesized by employing a flux method. The structure of BaMnB2O5 is composed of MnO5 square pyramids that form Mn2O8 dimers by edge-sharing and of pyroborate units ([B2O5]4−) that are composed of two corner-sharing trigonal–planar BO3 units. These building blocks share corners to form ∞2[MnB2O5]2− layers extending parallel to (100). The Ba2+ cations reside in the gap between two manganese pyroborate slabs with a coordination number of nine. The title compound forms an inter­esting spiral framework propagating along the 21 screw axis. The structure is characterized by two alternating layers, which is relatively rare among known transition-metal-based pyroborate compounds.

No MeSH data available.