Effect of the apical ligand on the geometry and magnetic properties of copper(ii)/mesoxalate trinuclear units

Abstract

Three new heterometallic metal–organic frameworks, namely, {(Ph₄P)₂[MnCu₃(Hmesox)₃Br(H₂O)]·H₂O}_n (1), {(Ph₄P)₂[CoCu₃(Hmesox)₃Br]}_n (2) and {(Ph₄P)₂[ZnCu₃(Hmesox)₃Br]·2.5H₂O}_n (3) were prepared and their structure and magnetic properties were investigated (H₄mesox = mesoxalic acid, Ph₄P⁺ = tetraphenylphosphonium). The structure of all the compounds consist of two interpenetrating opposite-chirality supramolecular cationic and polymeric anionic 3-D (10,3)-a networks, which results in chiral compounds. The anionic network is formed from the polymerization of [Cu₃(Hmesox)₃Br]⁴⁻ units, working as three connectors, and M(II) cations, working as three-connecting nodes, M = Mn(II), Co(II) and Zn(II). The Ph₄P⁺ cations build the cationic chiral supramolecular network opposite to the anionic one. Compounds 1 and 2 exhibit long-range magnetic ordering with critical temperatures of 7.2 K and 6.9 K, respectively. However, compound 3 does not display long-range order, but shows ferromagnetic and antiferromagnetic coupling among the Cu(II) ions. The magnetic interactions are studied by DFT calculations and compared with related Cu(II)-mesoxalate compounds previously reported.