Chain caesium borophosphates with B:P ratio 1:2: synthesis, structure relationships and low‐temperature thermodynamic properties. Issue 6 (9th December 2019)

• Record Type: Journal Article
• Authors: Shvanskaya, Larisa; Yakubovich, Olga; Krikunova, Polina; Ovchenkov, Evgeny; Vasiliev, Alexander
• Is Part Of: Acta crystallographica. Volume 75:Issue 6(2019:Dec.)
• Page Start: 1174
• Page End: 1185
• Publication Date: 2019-12-09
• Subjects: borophosphates -- structure relations -- straight chain -- chiral chain -- structural disorder -- tetrameric cluster -- thermodynamic properties -- magnetization plateau -- magnetocaloric effect -- hydrothermal synthesis
• DOI: 10.1107/S2052520619013763
• Languages: English
• ISSNs: 2052-5206

Abstract

Abstract : The crystal structures of three novel caesium borophosphates with chain‐type anionic fragments are reported. Relationships between new and known phases are discussed in terms of the effect of the initial crystallization medium on the structure. Abstract : Three caesium‐bearing borophosphates, Cs[BP2 O6 (OH)2 ] (I), Cs0.51 Mn1.17 (H2 O)2 [BP2 O8 ]·0.45H2 O (II) and CsMn[BP2 O8 (OH)] (III), were synthesized by a hydrothermal method at 473–523 K. Their crystal structures have been studied by means of single‐crystal X‐ray diffraction; all three structures comprise borophosphate chain anions with a B:P ratio of 1:2. The unique construction of (I) is based on four‐membered‐ring chains running parallel to the [010] direction. These protonated borophosphate chains are linked via hydrogen‐bond interactions to form a 3D framework with caesium cations incorporated. (II) is the first Cs and Mn 2+, Mn 3+ member of a known family characterized by [BP2 O8 ]∞ helical chains running along [001]. These chains are connected through MnO4 (H2 O)2 octahedra to form a 3D framework. The caesium cations are disordered over two independent positions in the channels, which they occupy together with water molecules. An additional MnO2 (H2 O)3 bipyramid statistically shares a common edge and two corners with three main Mn octahedra to form tetrameric clusters. The topological relation between the chain anionic fragments of (I) and (II) as well as the structural relation between (I) and previously studied boro‐ and berillophosphates are discussed. Compound (III) presents the first Mn member of the A I M III [BP2 O8 (OH)] family and is characterized by a 3D framework built by open‐branched borophosphate chains and MnO5 semi‐octahedra sharing vertices. The measurements of thermodynamic properties, i.e. magnetization M and specific heat C p, to 2 K and 30 T, provide evidence that (II) orders antiferromagnetically at the Néel temperature T N = 4.6 K and exhibits a plateau‐like feature under the action of an external magnetic field accompanied by a pronounced magnetocaloric effect.