Four Mixed 3d-4f 12-Metallacrown-4 Complexes: Syntheses, Structures and Magnetic Properties

The incorporation of Ln(III) ions into the 12-metallacrown-4 topology affords the formation of four mixed 3d-4f pentanuclear complexes of compositions [NH(C2H5)(3)]{[Ln(OAc)(4)] [12-MCMn(N)shiIII-4]}center dot xH(2)O (Ln = Sm (1), Gd (2), Tb (3), Dy (4); x = 0.5 for 1 and 3, x = 0.25 for 2, x = 0 for 4; H(3)shi = salicylhydroxamic acid). Compounds 1-4 were obtained from the reactions of H(3)shi with Mn(CH3COO)(2)center dot 4H(2)O and Ln(NO3)(3)center dot 6H(2)O, in the presence of N(C2H5)(3). They all contain a crown-like [Mn(4)Ln(mu-NO)(4)](11+) core with four Mn-III atoms being at the rim of the crown and an Ln(III) ion occupying the dome of the crown. The peripheral ligation about the core is provided by four eta(1):eta(1):mu acetate groups. The identity of the Ln(III) ions slightly affects the 12-metallacrown-4 frameworks, as demonstrated by the gradual decrease of the distances between the Ln(III) ions and the centres of the Mn-4 planes (1.85 angstrom for 1, 1.81 angstrom for 2, 1.80 angstrom for 3, and 1.77 angstrom for 4). Variable-temperature dc magnetic susceptibility studies were carried out on polycrystalline samples of 1-4. Antiferromagnetic interactions are determined for complexes 1-4.