Syntheses, crystal structures and magnetic properties of [2 x 1+1 x 2] heterotetrametallic and [1 x 1+1 x 1] heterodimetallic cocrystals of copper(II) and iron(II/III)

The present work reports syntheses, crystal structures and variable-temperature magnetic properties of three copper(II)-iron(II/III) compounds [{(CuL1)-L-II}{(FeL1)-L-III(H2O)(2)}](ClO4) (1), [{(CuLFeII)-L-II-Fe-1(H2O)(3)}{(CuL1)-L-II}(2)](-ClO4)(2) (2) and [{(CuLFeII)-L-II-Fe-2(H2O)(3)}{(CuL2)-L-II}(2)](ClO4)(2)center dot H2O center dot CH3COCH3 (3), where H2L1 = N,N'-ethylenebis(3-ethoxysalicylaldimine) and H2L2 = N,N'-o-phenylenebis(3-ethoxysalicylaldimine). Compounds 2 and 3 are tetrametallic [2 x 1 + 1 x 2] cocrystals of one diphenoxo-bridged dinuclear (CuFeII)-Fe-II and two mononuclear Cu-II moieties, while compound 1 is a dimetallic [1 x 1 + 1 x 1] cocrystal of one mononuclear Fe-III and one mononuclear CuII moieties. The overall topology of 1 is one-dimensional. Tetrametallic (in 2 and 3) and one-dimensional (in 1) self-assemblies are generated due to weak noncovalent interactions. Variable-temperature magnetic susceptibility measurements reveal that iron(II) or iron(III) centers in 1-3 remain in high-spin state. Compounds 2 and 3 exhibit weak antiferromagnetic interaction; the J values in the dinuclear core are -22.5 and -13.7 cm (1), respectively, compound 1 exhibits very weak antiferromagnetic interaction (J = -0.25 cm (1)) propagated through the weak noncovalent bonds. (C) 2011 Elsevier B.V. All rights reserved.