Transition metal phosphite complexes: from one-dimensional chain, two-dimensional sheet, to three-dimensional architecture with unusual magnetic properties

Abstract

Four new compounds, [Ni(HPO₃)(4,4′-bpy)(H₂O)₃]·4H₂O (1), [Co₂(HPO₃)₂(4,4′-bpy)₂(H₂O)₆]·9H₂O (2), [Zn(HPO₃)(4,4′-bpy)_0.5]·H₂O (3), and [Co₃(PO₃)₂(4,4′-bpy)₃(H₂O)₆]·3H₂O (4), have been synthesized. Compounds 1 and 2 are linear chains and isostructural except for the distinction of the metal ion and the number of lattice water molecules. Compound 3 consists of a 2D sheet structure. Compound 4 is a 3D magnetic porous material with 1D channels along the c axis. Magnetic measurements indicate that compound 1 shows paramagnetic behavior, while compound 2 displays antiferromagnetic behavior. Compound 4 exhibits antiferromagnetism with a pronounced field-induced spin–flop transition. A critical field of 3 T at 2.0 K is determined from the derivative dM/dH curve. Meanwhile, compound 4 shows a strong spin frustration arising from the geometric frustration in the kagomé lattice. The dehydrated phase 4a displays a characteristic of N₂ adsorption with type II isotherm. We performed detailed magnetic measurements for 4a, which exhibits quite different magnetic properties from 4. Compound 4a displays a ferrimagnetic behavior with a lower transition field of 0.2 T, and a weaker spin frustration.