Salen-Based Coordination Polymers of Iron and the Rare Earth Elements

Reaction of N,N′-bis­(4-carboxysalicylidene)­ethylenediamine
(H4L) with iron­(III) chloride and lanthanide nitrates resulted
in the coordination polymers of composition {[Ln2(FeLCl)2(NO3)2(DMF)5]·(DMF)4}n (Ln = Y, Eu, Gd, Tb, Dy). The
polymers consist of iron-salen-based moieties having carboxylate linkers
connected to rare earth atoms in a 1D chain structure. Thus, the iron-salen
complex acts as a “metalloligand”. Because of the twisting
of the chains, porous structures are formed and possess large free
void space. The magnetic studies of selected compounds exhibit weak
intramolecular antiferromagnetic interactions of Ln–Ln. At
3, 30, and 80 K, the Mössbauer spectra of the iron–dysprosium
compound show a strongly asymmetric quadrupole doublet with isomer
shift and quadrupole splitting values typical for FeIII ions in high spin state. In addition, an anomalous temperature dependence
of both isomer shift and quadrupole splitting has been observed.