Mononuclear Fe(III) and tetranuclear [Fe(III)Gd(III)] 2 complexes with a Schiff-base ligand derived from the o-vanillin: Synthesis, crystal structures and magnetic properties

Abstract

The mononuclear high-spin iron(III) complexes [Fe(3-MeOsalpn)Cl(H 2O)] ( 1) and [Fe(3-MeOsalpn)(NCS)(H 2O)]·0.5CH 3CN ( 2) and the tetranuclear oxo-bridged compound [{Fe(3-MeOsalpn)Gd(NO 3) 3} 2(μ-O)]·CH 3CN ( 3) [3-MeOsalpn 2− = N, N′-propylenebis(3-methoxysalicylideneiminate)] have been prepared and magneto-structurally characterised. The iron(III) ion in 1 and 2 is six-coordinated in a somewhat distorted octahedral surrounding with the two phenolate-oxygens and two imine-nitrogens from the Schiff-base building the equatorial plane and a water ( 1 and 2) and a chloro ( 1)/thiocyanate-nitrogen ( 2) in the axial positions. The neutral mononuclear units of 1 and 2 are assembled into centrosymmetric dinuclear motifs through hydrogen bonds between the axially coordinated water molecule of one iron centre and methoxy-oxygen atoms from the Schiff-base of the adjacent iron atom. The values of the intradimer metal–metal distance within the supramolecular dimers are 4.930 ( 1) and 4.878 Å ( 2). The tetranuclear of 3 can be described as two {Fe III(3-MeOsalpn)} units connected through an oxo-bridge, each one hosting a [Gd III(NO 3) 3] entity in the outer cavity defined by the two phenolate- and two methoxy-oxygen atoms. The values of the intramolecular Fe⋯Fe and Fe⋯Gd distances in 3 are 3.502 and 3.606 Å, respectively. The analysis of the magnetic data of 1– 3 in the temperature range 1.9–300 K shows the occurrence of weak intermolecular antiferromagnetic interactions in 1 and 2 [ J = −0.76 ( 1) and −0.75 cm −1 ( 2) with the Hamiltonian defined as H = − JS Fe1· S Fe1] whereas two intramolecular antiferromagnetic interactions coexist in 3, one very strong between the two iron(III) ions ( J 1) through the oxo bridge and the other much weaker between the iron(III) and the Gd(III) ions ( J 2) across the double phenoxo oxygens [ J 1 = −275 cm −1 and J 2 = −3.25 cm −1, the Hamiltonian being defined as H = - J 1 S Fe 1 · S Fe 1 ′ - J 2 ( S Fe 1 · S Gd 1 + S Fe 1 ′ · S Gd 1 ′ ) ]. These values are analysed in the light of the structural data and compared with those of related systems.