Abstract
Three novel tetranuclear macrocyclic complexes, [(CuL1)3Cr](ClO4)3·3H2O (1), [(CuL2)3Cr](ClO4)3·3H2O (2) and [(CuL3)3Cr](ClO4)3·3H2O (3) [L1, L2 and L3 are the dianions of three [14]N4 and [15]N4 macrocyclic oxamides, namely 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene,2,3-dioxo-5,6:13,14-dibenzo-9-methyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene and 2,3-dioxo-5,6:14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclotetradeca-7,12-diene, respectively], have been prepared and characterized. These complexes are the first examples of Cu3Cr species exhibiting spin topology with all the spins parallel in the ground state. Cryomagnetic studies on (1) (2–300 K) and (3) (77–300 K) revealed that the CuII and CrIII ions interact ferromagnetically through the oxamido bridge, with the exchange integral J = 6.7 cm−1 for (1) and J = 6.3 cm−1 for (3) based on Ĥ = −2J∑ŜiŜj. The ferromagnetic interaction has been rationalized in terms of strict orthogonality of the magnetic orbitals. The oxamido bridge is also more efficient than the oxalato bridge at propagating the ferromagnetic interaction.
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