Direct Synthesis, Crystal Structure, High-Field EPR, and Magnetic Studies on an Octanuclear Heterometallic Cu(II)/Cd Complex of Triethanolamine

Abstract

The reaction of zerovalent copper with cadmium iodide and triethanolamine (H₃L) in dimethylformamide (dmf) carried out under open-air conditions afforded a novel heterometallic complex [Cu₃(HL)₃CdI₂]₂·4dmf. The crystal lattice consists of an octanuclear molecule [Cu₃(HL)₃CdI₂]₂, which has an inversion center at the midpoint of the central Cu₂O₂ unit, and of two non-coordinating dmf molecules. Eight metal atoms linked by alkoxide arms of triethanolamine ligands form a zigzag Cd−Cu1−Cu2−Cu3−Cu4−Cu5−Cu6−Cd chain with the separations between bridged Cu atoms in the range 2.935(2)−3.403(2) Å. The complex is further stabilized by intramolecular O−H···O hydrogen bonds. High-field electron paramagnetic resonance (EPR) spectra of the S = 1 spin state with D_(S=1) = −0.843 cm⁻¹, E_(S=1) = −0.081 cm⁻¹ were observed. Fitting the magnetic susceptibility temperature dependence by using the exchange Hamiltonian H_HDVV= J₁(S₁S₂+ S₅S₆) +J₂(S₂S₃+ S₄S₅ )+ J₃S₃S₄, to which terms expressing the zero-field splitting and Zeeman splitting of the ground S = 1 state were added, resulted in J₁ = 68, J₂ = 19, J₃ = −57 cm⁻¹. “Broken symmetry” DFT calculations correctly predicted the triplet ground state of the hexa-copper system.