Lamellar crystal structure and Haldane magnetism in NH${}_4$VPO${}_4$OH

A novel vanadium hydroxide-phosphate, NH${}_4$VPO${}_4$OH, was synthesized hydrothermally in V${}_2$O${}_5$ - NH${}_4$H${}_2$PO${}_4$-citric acid system at 230 °C. It was characterized by XRD, TG-DSC, SEM-EDX, FTIR and NMR spectroscopy. NH${}_4$VPO${}_4$OH is isostructural with NH${}_4$GaPO${}_4$OH and features edge-sharing chains of VO${}_6$ octahedra. These chains running along [010] direction of the unit cell are connected by phosphate tetrahedra to form infinite layers parallel to the (100) plane. Ammonium cations are embedded between the heteropolyhedral layers. According to the thermodynamic and NMR measurements supported by the first-principles calculations, NH${}_4$VPO${}_4$OH presents a rare case of Haldane spin system with spin S=1 based on V${}^{3+}$ ions. (© 2023 Wiley‐VCH GmbH)