Synthesis, crystal structure, magnetic property and DFT calculations of an unusual dinuclear μ2-alkoxido bridged iron(III) complex

A new dinuclear di(mu-alkoxido) bridged complex [Fe2L2] (1) (H3L = N,N'-bis{1-(2-hydroxyphenyl)-ethylidene}-2-hydroxy-1,3-propanediamine) has been synthesized and characterized. The structure of 1 consists of a centrosymmetric dimer where two crystallographically equivalent metal ions are asymmetrically bridged by two alkoxido oxygen atoms. In the structure, each ligand coordinates to one Fe(III) centre and consequently the imino nitrogen atoms are in cis positions, which is rather unusual for this ligand. Variable-temperature magnetic susceptibility measurements of the complex indicate that the two iron(III) centres are antiferromagnetically coupled (J = -17.46 cm(-1)). The exchange mechanism has been investigated by means of DFT calculations. In addition, the theoretical study has been also used to rationalize the unusual coordination mode of the Schiff base ligand. Moreover, the influence of the weak forces or solvent molecules present in the solid-state structure for the conformational change is also analysed theoretically. This theoretical calculation incorporates two more similar structures, [Fe2L'(2)]center dot CH2Cl2 (2) and [Fe2L'(2)] center dot 2CH(3)CN (3) (H3L' = N, N'-bis(salicylidene)-1,3,-diaminopropan-2-ol), for a comparative study. Complex 2 has been reported previously in the literature with the usual binding mode of the ligands. We have repeated its synthesis and recrystallized it from another solvent (acetonitrile) to get complex 3 which is isostructural with 2 but has acetonitrile as solvent molecule.