Synthesis, Structures, and Magnetic Investigations of Nickel Phosphates: Ni 2 (PO 4 )(OH), Ni 7 (PO 4 ) 3 (HPO 4 )(OH) 3 , and NaNiPO 4 Including Potential Haldane Behavior.

Three novel nickel-phosphate structures are reported, Ni 2 (PO 4 )(OH) ( I ), Ni 7 (PO 4 ) 3 (HPO 4 )(OH) 3 ( II ), and NaNiPO 4 ( III ). Each new system was prepared via a high-temperature hydrothermal synthesis at 600-650 °C. All three compounds are built of quasi-one-dimensional (quasi-1-D) Ni 2+ containing chains with varying phosphate bridging modes and were characterized by single crystal X-ray diffraction and magnetic susceptibility. All three compounds display very different magnetic behavior. Anisotropic magnetic data is reported for Ni 2 (PO 4 )(OH) ( I ) exhibiting slow antiferromagnetic ordering in the high-temperature regime with substructures that begin to form below 32 K at different field strengths. These characteristics affirm I as being one of the few Haldane-like material candidates. The Ni 7 (PO 4 ) 3 (HPO 4 )(OH) 3 ( II ) material is a member of the unusual ellenbergerite structural family and displays complex inter- and intrachain magnetic interactions while NaNiPO 4 ( III ) shows antiferromagnetic ordering near 18 K. This magnetic behavior is correlated with their structures.