Syntheses and crystal structures of iron co-ordination polymers with 4,4′-bipyridine (4,4′-bpy) and 4,4′-azopyridine (azpy). Two-dimensional networks supported by hydrogen bonding, {[Fe(azpy)(NCS)2(MeOH)2]·azpy}n and {[Fe(4,4′-bpy)(NCS)2(H2O)2]·4,4′-bpy}n

Abstract

New iron(II) co-ordination polymers, {[Fe(azpy)(NCS)₂(MeOH)₂]·azpy}_n 1 (azpy = 4,4′-azopyridine), {[Fe(4,4′-bpy)(NCS)₂(H₂O)₂]·4,4′-bpy}_n 2 (4,4′-bpy = 4,4′-bipyridine) and {[Fe(azpy)₂(NCS)₂]·3H₂O}_n 3 have been synthesized and characterized. The crystal structures of both compounds 1 and 2 contain two types of bridging ligands; one is of the co-ordination bond type, directly bridging iron centers to form a one-dimensional chain of [Fe(L)] (L = azpy or 4,4′-bpy), while the other links these chains by hydrogen bonds between the pyridine nitrogen atoms and co-ordinated methanol or water molecules, resulting in a grid sheet. Each sheet shows non-interpenetration because of incorporation of NCS anion in the grid. Cyclic voltammograms of 1 and 3 demonstrate that the directly bridging azpy ligands show no apparent redox activity, whereas a reversible redox wave observed for 1 is attributed to the hydrogen-bonding supported azpy. Magnetic susceptibilities measured from 1.9 to 300 K are indicative of no appreciable magnetic exchange interaction between the adjacent metal ions.