Heterodinuclear [Co-Ln] complexes of semicarbazide-arm bearing ligand: synthesis from the cleavage of starting [Co-Co] complex, structures and magnetic properties

Abstract

The heterometallic bridging potential of the anion of 1-(2-hydroxy-3-methoxybenzylidene)semicarbazide (HL) to Co^II and four 4f ions was examined during a 4f ion coordination-driven cleavage of [Co₂(μ-OH₂)(O₂CCMe₃)₄(HO₂CCMe₃)₄] (Co₂-Piv) and scrambling of pivalate anions from the starting material. Room-temperature reactions with four different lanthanide nitrate salts yielded [CoLnL(μ₂-OOCCMe₃)₄(CH₃OH)]·3CH₃OH [Ln = Gd (1), Tb (2), Dy (3) and Ho (4)]. The formation in solution and the crystallization in the solid state indicated that the reactions inhibit any further aggregation of Co-Ln cores to higher order aggregates. After scrambling, the pivalate ions in [Co-Ln] show three types of coordination modes to sustain the dinuclear aggregates with varying degrees of distortion in the dinuclear entities bound to a single L⁻ ion. Atom economy was maintained with respect to the pivalate ions as no external addition of these anions was made. The dc magnetic measurements revealed the presence of weak ferromagnetic interactions in complexes 1 and 2 and weak antiferromagnetic interactions in complexes 3 and 4.