Channel-containing criss-crossed and hydrogen-bonded one-dimensional coordination polymers of iron(III) and (II) with 4,4'-bipyridine: Hydrothermal syntheses, structures, absorption and Mossbauer studies showing spin crossover for the iron(III) polymer

The iron -4,4'-bi pyridine coordination polymers (1)(infinity)[(FeNO3)-N-III)2(mu-4,4'-bipy)(H2O)(2)](OHH2O)-H-. (1) and (1)(infinity) [Fe-III(H2PO4)(2-)(mu-4,4'-bipy)(H2O)](H2O.)-H-.(4,4'-bipy)} (2) have been synthesized by hydrothermal methods. The structure of 1 is a channel-containing open framework constructed through the hydrogen-bond supported criss-cross arrangement of the 1D Fe-bipy chains. Fe-57 Mossbauer spectroscopy reveals a gradual spin crossover behavior for 1 with a magnetic ordering at low temperature. The structure of 2 is constructed from parallel oriented, hydrogen-bonded ID Fe-bipy chains. The 4,4'-bipyridine solvate in 2 is held by hydrogen bonding between the H2PO4 groups on adjacent iron centers along the chain and is situated in a pi-pi stacking contact to the coordinated 4,4'-bipy ligand. The chains in 2 are interconnected through hydrogen bonding to a three-dimensional supramolecular network. Crystals of 2 appear dark red or orange depending on the orientation (pleochroism, dichroism).