Syntheses, Characterization and X-ray Crystal Structure of Polymeric Heteronuclear Oxo-bridged Fe/Na Assembled with Salen-type Schiff Base and Dicyanamide

Reaction of FeCl2.4H2O with 2-(-(2-(-2-hydroxy-3-methoxybenzylideneamino)phenylimino)methyl)-6-methoxyphenol (H2L) gives the metalloligand [Fe(L)].(H2O) (1). Reaction of metalloligand (1) with three fold of sodium dicyanamide Na[N(CN)2] gives the new tetranuclear compound [{FeIINaI(L)(EtOH)(HN(CN)2)}(μ-O){FeIIINaI(L)(NO3)]}]n (2) in which one of the two irons is oxidized to +3. Suitable crystals of (2) were grown by slow evaporation of ethanol solution during two weeks. The metalloligand (1) and the tetranuclear (2) complexes are characterized by IR and physical measurement. Spectroscopic evidence indicated that the Schiff base H2L behave an N2O2O’2 coordination tetradentate ligand. The structure of (2) was elucidated by X-ray diffraction analysis. The asymmetric unit of the compound contains two dideprotonated ligand molecules, two iron ions, one hexacoordinated sodium ion, one heptacoordinated sodium ion, one bidentate nitrate group, one monodentate dicyanamide unit, one coordinated ethanol molecule and an O2- ion which acts as a bridge between the FeII and the FeIII of two entities: [FeIINaI(L)(EtOH)(HN(CN)2)] and [FeIIINaI(L)(NO3)]. Bridge Fe—O(μ) bond lengths are 1.7813(14) and 1.7856(13) A and bridging angle Fe—O—Fe is 144.78(8)°. The second terminal cyano group of the dicyanamide link another molecule complex through the heptacoordinated NaI leading a polymeric structure. Intermolecular hydrogen bond connect the polymeric chains to develop a three dimensional structure.