The structure and magnetic properties of the two-dimensional dipyrazine-bridged polymers M(pz)(2)Br-2 (M = Fe-II, Co-II, Ni-II)

The polymeric compounds M( pyrazine)(2)Br-2 [M = Fe (1), Co (2), and Ni (3)] have been synthesized by the addition of a solution of pyrazine in methanol to a methanolic solution of the anhydrous metal bromide. The crystal structures of (1)-(3) were determined using powder synchrotron and neutron diffraction data and were found to be isostructural. The structures consist of pseudo-octahedral units, doubly linked by pyrazine ligands to form two-dimensional sheets. Magnetic susceptibility data were recorded for each complex down to 5 K and reveal paramagnetic behaviour at high temperatures and antiferromagnetic interactions at low temperatures. Comparison of the structures and magnetism of these and other M(pz)(2)X-2 compounds highlight the relative importance of the canting of the pyrazine ligands on the strength of the magnetic exchange.