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^II₇(L)₄(μ₃-OH) ₂(H₂O)₂(DMF)₂][ClO₄] ₄·4H₂O (1) [L(2-): N-{CH₂CH ₂(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^II₃(μ 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.