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

The mononuclear high-spin iron(III) complexes [Fe(3-MeOsalpn)Cl(H2O)] (1) and [Fe(3-MeOsalpn)(NCS)(H2O)]center dot 0.5CH(3)CN (2) and the tetranuclear oxo-bridged compound [{Fe(3-MeOsalpn)Gd(NO3)(3)}(2)(mu-O)]center dot CH3CN (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 angstrom (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(NO3)(3)] entity in the outer cavity defined by the two phenolate- and two methoxy-oxygen atoms. The values of the intramolecular Fe center dot center dot center dot Fe and Fe center dot center dot center dot Gd distances in 3 are 3.502 and 3.606 angstrom, 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)center dot 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-Fe1 center dot S-Fe1' - J(2) (S-Fe1 center dot S-Gd1 + S-Fe1' center dot S-Gd1')] These values are analysed in the light of the structural data and compared with those of related systems. (C) 2011 Elsevier Ltd. All rights reserved.