Crystal Structures and Low-Dimensional Ferromagnetism of Sodium Nickel Phosphates Na5Ni2(PO4)3·H2O and Na6Ni2(PO4)3OH

• Published in: Inorganic chemistry Vol. 58; no. 1; pp. 610 - 621
• Main Authors: Kirsanova, Maria A, Aksyonov, Dmitry A, Maximova, Olga V, Shvanskaya, Larisa V, Vasiliev, Alexander N, Tsirlin, Alexander A, Abakumov, Artem M
• Format: Journal Article
• Language: English
• Published: American Chemical Society 07.01.2019
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.8b02791

Two new sodium nickel phosphates, Na5Ni2(PO4)3·H2O (I) and Na6Ni2(PO4)3OH (II), have been synthesized hydrothermally and characterized by synchrotron X-ray diffraction, electron diffraction, low-temperature thermodynamic and magnetic measurements, and ab initio calculations. Unlike the majority of Ni2+ compounds, I and II show predominant ferromagnetic exchange couplings. I crystallizes in the monoclinic space group P21/n (a = 14.0395(4) Å, b = 5.1847(14) Å, c = 16.4739(4) Å, β = 110.4186(14)°) and features chains of ferromagnetically coupled Ni2+ ions. In II with the orthorhombic space group Pcmb (a = 7.5007(15) Å, b = 21.4661(4) Å, c = 7.1732(15) Å), the ferromagnetically coupled Ni2+ ions form dimers arranged on a spin ladder. Both compounds represent rare examples of quasi-one-dimensional ferromagnets. Structural features behind this unusual magnetic behavior are discussed.