Temperature induced single-crystal-to-single-crystal transformations and structure directed effects on magnetic properties.
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.
Legrand
Yves-Marie
YM
Institut Européen des Membranes-Centre National de la Recherche Scientifique, UMR-5635, Place Eugène Bataillon, CC 047, Montpellier Cedex 5, France.
van der Lee
Arie
A
Masquelez
Nathalie
N
Rabu
Pierre
P
Barboiu
Mihail
M