Self-assembly of Schiff base anions and the trapping of HO−, O2− and Piv− bridges in a family of Ni3Ln4 complexes: synthesis, structures and magnetic properties

Abstract

A unique family of heptanuclear 3d–4f complexes, [Ni₃Ln₄L₃(OH)₃O(Piv)₆(MeOH)₂(OMe)]·nH₂O (Ln = Dy (1), Tb (2), Ho (3); Piv = Me₃CCO₂⁻), has been synthesized using a Schiff-base H₂L (L = 2-((2-hydroxy-3-methoxybenzylidene)amino)benzoic acid), NEt₃, NiCl₂·6H₂O and Ln(NO₃)₃·5H₂O in a refluxing MeOH–CHCl₃ solvent mixture. Single-crystal X-ray diffraction studies revealed that the coordination aggregates were grown around a unique μ₄-O²⁻ unit, which connects four lanthanide ions. Three supporting μ₃-HO⁻ ions were used to connect three L²⁻-bound Ni⋯Ln fragments to the central Ln^III center, which is not coordinated to any Schiff-base anion. Six μ_1,3-pivalate anions extended further support for the three L²⁻-bound Ni⋯Ln fragments and three Ln⋯Ln fragments. Magnetic studies of 1–3 in the solid state are consistent with weak antiferromagnetic interactions between the 3d and 4f ions.