A 2D homochiral inorganic–organic framework exhibiting a spin–flop transition

Abstract

A 2D homochiral inorganic–organic framework {[Mn(NPTA)(4,4′-bpy)(H₂O)]·(H₂O)₂}_n was prepared by assembling achiral polar 4-nitrophthalic acid, manganese ions, and ancillary 4,4′-bipyridine ligands (NPTA = 4-nitrophthalate) (4,4′-bpy = 4,4′-bipyridine). The isomorphous Zn(II) compound was also prepared as a diamagnetic analogue. Adjacent manganese spin centres are linked by the syn–anti carboxylate to form a helical chain, and chains of the same chirality are connected by 4,4′-bpy ligands to generate a homochiral layered framework. Edge-to-face aromatic interactions between neighboring layers lead to a 3D homochiral supramolecular structure. Magnetization and heat capacity measurements indicate that the framework is a weak antiferromagnet at low applied field. The magnetic interactions between adjacent manganese ions in the helical chain can be fitted using the 1D Fisher model, with 2J/k = −0.68 K and g = 2.00. Moreover, the compound displays a unique field-dependent spin–flop transition in high magnetic fields, with a critical field of 23.6 kOe at 1.9 K.