Magnetic and electrical properties of a cyanide-bridged CoCu3 cluster featuring square pyramidal Cu(ii) centers

Abstract

Molecular magnetic materials showing magnetic and electrical bifunctionality are highly attractive; however, the construction of such materials is relatively difficult. Herein, a cyanide-bridged CoCu₃ cluster, {[Co^III(CN)₆][Cu^II(TMC)]₃}[[Co^III(CN)₆]]·14H₂O, based on the Cu(II) complex of methyl cyclam (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and hexacyanidocobaltate(III), has been prepared and characterized in terms of structure, magnetic properties, and proton conduction. The tetranuclear CoCu₃ cluster exhibits a T-shaped structure with three square pyramidal Cu^II (S = 1/2) centers separated by a diamagnetic [Co^III(CN)₆]³⁻ anion (S = 0). The highly hydrogen-bonded water clusters in the 1D pores of the 3D supramolecular network yield proton conductivities of 5.3 × 10⁻³ S cm⁻¹ at 50 °C under 95% RH. A pronounced temperature sensitivity in both conductivity and activation energy, with a value of 0.32 eV, points towards the operation of the Grotthuss mechanism for proton transportation, which is facilitated by a large amount of lattice water molecules. Magnetic studies reveal easy-axis magnetic anisotropy of the Cu²⁺ ions in a distorted square pyramidal geometry. Interestingly, field-induced slow magnetic relaxation occurring via direct and Raman processes was observed for this complex. This compound is the first example of a Cu^II complex combining slow magnetic relaxation and proton conduction, highlighting the design and construction of magnetic-electrical materials through cyanide-bridged assemblies.