Phase Control of Ferromagnetic Copper(II) Carbonate Coordination Polymers through Reagent Concentration

A significant degree of control over the dimensionality and magnetic connectivity of Cu-II carbonate coordination polymers is achieved through varying the concentration of ammonia in the reactant solution. Higher concentration leads to a two-dimensional ferromagnetic [Cu-3(2,4 '-bipy)(6)(CO3)(2)](n)(2n+) kagome structure while lower concentration develops a ferromagnetic [Cu(2,4 '-bipy)(2)(H2O)(2)][Cu(2,4 '-bipy)(2)(CO3)(2)] chain (where 2,4 '-bipy = 2,4 '-bipyridine). The carbonate anion in the structures arises from the fixation of atmospheric CO2 by the basic ammonia solution. Modelling the magnetic susceptibility of 1 and 2 reveals ferromagnetic interactions with J/k(B) = +28.1 K for 1 and +13.99 K for 2. (H = -J). The use of a monodentate polypyridine ligand results in the suppression of the superexchange pathway between layers in 1, removing the metamagnetic behaviour seen in related compounds where a ditopic ligand presents the ability for the layer to couple antiferromagnetically. Attempts to substitute 2,4 '-bipy for 4-(N,N-dimethylamino)pyridine (4-dmap) result in a discrete species [Cu(4-ampy)(4)](ClO4)(2) (3).