Single molecule magnet behaviour of CoIIILnIII (Ln = TbIII, GdIII) compounds with compartmental Schiff base ligand and sulfonate co-ligands

•Two heteronuclear 3d-4f complexes (Ln = Tb, Gd) were synthesized using the compartmental Schiff base ligand and secondary sulfonate co-ligands.•These compounds represent rare instances of dinuclear Co(III)-Ln(III) SMMs.•These findings demonstrate the practicality of creating sulfonate-based Co(III)-Ln(III) coordination complexes, despite sulfonate's generally weak bonding with metal ions.•This research not only broaden the structural diversity of 3d-4f complexes but also provide a valuable experimental basis for further exploration of their magnetic properties. In this research, our team synthesized and characterized two heteronuclear 3d-4f complexes, [CoIIICl(μ-valen)(μ-4-HBS)LnIII(NO3)(H2O)(4-HBS)], with Ln representing Tb (1) and Gd (2). Achievement of this was through the utilization of a compartmental Schiff base ligand H2valen, alongside secondary co-ligands Na(4-HBS) [H2valen=6,6′-((1E,1′E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))bis(2-methoxyphenol); Na(4-HBS)=sodium 4-hydroxybenzenesulfonate]. X-ray crystallography revealed that both complexes feature a similar [Co(III)-Ln(III)] core, connected by the phenoxo-O atoms from the compartmental Schiff base ligand and the sulfonate-O atoms from the co-ligand. In this context, Co(III) displays a distorted octahedral geometry within a CoN2O3Cl coordination sphere, while Ln(III) exhibits a muffin (MFF)-like distorted geometry in a LnO9 coordination sphere. Magnetic analysis shows that the two complexes display unique magnetic properties. Complex 1 exhibits pronounced SMM behavior, with a notable energy barrier of 14.8 K for magnetization reversal. However, complex 2 presents a minor energy barrier of 4.8 K. Additionally, complexes 1 and 2 represent uncommon examples of dinuclear Co(III)-Ln(III) SMMs. [Display omitted]