A unique heteropentanuclear CuII2CoIICoIII2 complex, synthesised from metallic Cu and Co acetate in the presence of triethanolamine.: Magnetic properties and a strong H-bond stabilised lattice

Reaction of zerovalent copper with cobalt(ii) acetate and triethanolamine (H(3)Tea) in DMF solution in air yields the unique pentanuclear mixed-valence complex [(Cu2CoCO2III)-Co-II-C-II(O2CMe)(4)(H(2)Tea)(2)(Tea)(2)].2(HO2CMe), 1, which has been characterized by a range of spectroscopic methods and structurally by X-ray crystallography. In the centrosymmetric unit of 1 five metal ions are linked together by eight oxygen atoms of the four triethanolamine ligands and by two acetate anions in the sequence Cu(ii)-Co(iii)-Co(ii)-Co(iii)-Cu(ii), with the metal-metal separations being 2.823(2) and 2.964(1) Angstrom for Cu(ii). . . Co(iii) and Co(iii). . . Co(ii), respectively. Discrimination between Co(ii) and Co(iii) atoms is based on bond length considerations; the Co(iii) is low spin. The lattice hydrogen-bonded network involving the non-coordinating acetic acid molecules links the pentanuclear units together and results in the formation of an extended one-dimensional structure. Magnetic measurements for 1 showed a marked decrease of the chiT value at low temperature, indicative of antiferromagnetic interactions between magnetic centres. A fit was attempted assuming an effective S=1/2 ground state for Co(ii) and an Ising-type anisotropy, considering only intramolecular interactions. The obtained value for J(z) of 36 cm(-1) must originate from the efficient role of the diamagnetic Co(iii) in transmitting the interaction between Cu(ii) and Co(ii) below 40 K.