Rational synthesis of a heterotetranuclear CrIII2CuII2 species using a metaloximate as a building block. A magnetostructural study

The reaction of [Cu(DapdoH(2))2](2+) ions with [Cr(III)L(MeOH)2Br](2+) ions (L = 1,4,7-trimethyl-1,4,7-triazacyclononane; DapdoH(2) = 2,6-diacetylpyridine dioxime) produced in situ in methanol, yielded, in the presence of triethylamine, the complex [L(2)Cr(III)(2)(Dapdo)2(OH)2Cu(II)(2)Br(2)](ClO(4))2. It has been characterized on the basis of elemental analysis, IR spectroscopy and variable-temperature (2-298 K) magnetic susceptibility measurements. The molecular structure established by X-ray diffraction consists of a [Cr(III)(2)(micro-NO)4(micro-OH)2Cu(II)(2)](4+)-core, which can be considered as two edge-sharing triangular CrCu(2)-units. The variable-field variable-temperature magnetic measurements revealed a ground state of S(t) = 2 with uncommon antiferromagnetic exchange interactions between the chromium(III) and copper(II) centers: J(A) = -79 +/- 2 cm(-1), J(B) = -17 +/- 1.7 cm(-1), where J(A) represents the interactions through a combination of oximate (>N-O-) and a hydroxo-bridging, while J(B) is the exchange through only a two-atom oximate (>N-O-) group.