Synthesis, structures and magnetic properties of a series of 3d-4f tetranuclear CoII2LnIII2 cubanes

Abstract

The reaction of 2,6-pyridinedimethanol (pdmH₂), CoCl₂·6H₂O, Ln(NO₃)₃·6H₂O and pivalic acid (pivH) in the presence of triethylamine in MeCN and CH₂Cl₂ under ambient conditions results in the tetranuclear heterobimetallic compounds [Co^II₂Ln₂(pdmH)₄(Piv)₆]·4CH₃CN (Ln = Y (1), Gd (2), Tb (3), Ho (4)) and [Co^II₂Dy₂(pdmH)₄(Piv)₆]·2CH₃CN (5). The molecular structures of 1–5 were determined by single-crystal X-ray diffraction and reveal that they are isostructural. However, compounds 1–4 crystallize in the monoclinic space group P2₁/n, while compound 5 crystallizes in the orthorhombic space group Pnna. In all of these compounds, the four metal ions are held together by four alkoxide μ₃-RCH₂O⁻ bridges to form novel Co₂Ln₂O₄-heterocubanes. Magnetic properties of 1–5 have been investigated using dc and ac susceptibility measurements. Of these compounds, only compound 5 displays an out-of-phase signal in the ac susceptibility and exhibits slow relaxation of the magnetization, which is attributed to the presence of the anisotropic Dy^III ions.