Square and Butterfly Tetranuclear [Co₂Ln₂] Clusters Built from the Same Building Blocks but Displaying Different Magnetic Properties: Structural Variation by Means of Solvent and the Radii of Ln³⁺ Ions

Abstract

Abstract Two series of tetranuclear [Ln 2 Co 2 ] clusters were built from the same [Co(CDTA)] 2– building blocks but have different metal skeletons: square 1Ln compounds {[Ln 2 Co 2 (CDTA) 2 (μ 4 ‐OH)(DMF) 2 (H 2 O) 6 ] · ClO 4 · 1.5H 2 O; Ln = La, Gd, and Dy} with a μ 4 ‐OH – bridged Ln–Co–Ln–Co arrangement, and two μ 3 ‐OH – ‐bridged “butterfly” 2Ln compounds {[Ln 2 Co 2 (CDTA) 2 (μ 3 ‐OH) 2 (H 2 O) 6 ] · 6H 2 O; Ln = Gd, Tb, Dy, and Y} with two Ln 3+ ions as the “body” and two Co 2+ ions as “wings”. They were prepared from the solvothermal reactions of trans ‐1,2‐diaminocyclohexane‐ N , N , N′ , N′ ‐tetraacetic acid (H 4 DCTA), Ln(ClO 4 ) 3 , and Co(ClO 4 ) 2 in DMF/H 2 O or H 2 O solvent. Their syntheses are mainly controlled by the solvent and the radii of Ln 3+ ions. Light Ln 3+ ions with big radii are favorable for the formation of square complexes, whereas heavy Ln 3+ ions (including Y 3+ ) with small radii promote the formation of butterfly ones. Remarkably, the middle Ln 3+ ions are favorable for the formation of both structures, and in these cases the reactions are controlled by solvent (H 2 O or H 2 O + DMF). Magnetic analyses reveal the antiferromagnetic interactions between the two Co 2+ ions in 1La and 2Y . Interestingly, other butterfly clusters ( 2Gd , 2Tb , 2Dy ) show dominant ferromagnetic interactions, whereas the other square clusters ( 1Gd , 1Dy ) show overall antiferromagnetic interactions. Details of the magnetic interaction between the metal ions are discussed.