Temperature Induced Single-Crystal-to-Single-Crystal Transformations and Structure Directed Effects on Magnetic Properties

Abstract

The binding of CoII, NiII, and CuII cations to the lithium 3-pyridinesulfonate ligand in an aqueous solution leads to single crystals of coordination polymers 1-3. The solid-state architectures of 1-3 which resulted from the combination of ligand-water heterocomplexation processes are linear coordination polymers packed into parallel alternatively stratified layers. These layers are interconnected through intermolecular hydrogen-bonding interactions occurring between the coordinated water molecules and the noncoordinating oxygen atoms of the sulfonate groups. Consequently, this leads to the formation of the cross-linked 3D (1, 2) or layered 2D (3) networks exhibiting 12-point or four-point hydrogen bond contacts between each unit with eight or four adjacent neighbors, respectively. The reversible structural rearrangement of these frameworks proceeds from the "relaxed" room-temperature phase to the "contracted" low-temperature phase in response to an external thermal stimulus. The reversibility of the contraction/relaxation process has been tested and confirmed by X-ray analysis. Motions toward shortening intermolecular distances have the consequence of increasing the degree of magnetic interaction between the metal ions. The magnetic measurements carried out in the range 1.8-400 K on the three compounds show an unusual change from antiferromagnetic to ferromagnetic behavior related to the structural variations recorded at low temperatures and to the loss of water above 350 K.