Unprecedented heptacopper(II) cluster with body-centred anti-prismatic topology. Structure, magnetism and density functional study

Using a (2-pyridyl) ethylamine-appended carboxylate ligand a new cluster [Cu-7(II)(L)(4)(mu(3)-OH)(2)(H2O)(2)(DMF)(2)][ClO4](4)center dot 4H(2)O(1) [L(2-): N-{CH2CH2(2-pyridyl)}(CH2CH2CO2)(2)] is synthesized, as a result of 'coordination-driven self-assembly'. The structure of 1 is unique and consists of a centrosymmetric carboxylato-and hydroxo-bridged heptanuclear copper(II) cation, with body-centred anti-prismatic topology. The four crystallographically independent copper(II) centres differ markedly in their coordination geometry. In addition to establishing cluster authenticity, the structural analysis of 1 discloses two notable features. The existence of {Cu-3(II)(mu(3)-OH)}(5+) core and H-bonded metal-coordinated carboxylate and water unit, with water acting as a proton donor. Both of these features have biological implications. Magnetic measurements reveal that in this unprecedented cluster the net magnetic-exchange is antiferromagnetic. The different types of magnetic-exchange coupling constants (J values) considered for magnetic data analysis appear to adopt a variety of values depending on the specific geometric parameters associated with two interacting copper(II) centres. Notably, for 1 a good agreement between the J values obtained from DFT calculations at the B3LYP level of theory and from the experimental data is achieved.