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

The reaction of 2,6-pyridinedimethanol (pdmH(2)), CoCl(2)·6H(2)O, Ln(NO(3))(3)·6H(2)O and pivalic acid (pivH) in the presence of triethylamine in MeCN and CH(2)Cl(2) under ambient conditions results in the tetranuclear heterobimetallic compounds [Co(II)(2)Ln(2)(pdmH)(4)(Piv)(6)]·4CH(3)CN (Ln = Y (1), Gd (2), Tb (3), Ho (4)) and [Co(II)(2)Dy(2)(pdmH)(4)(Piv)(6)]·2CH(3)CN (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 P2(1)/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 mu(3)-RCH(2)O(-) bridges to form novel Co(2)Ln(2)O(4)-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.