Control of nuclearity in heterometallic CuII–MnII complexes derived from asymmetric Schiff bases: structures and magnetic properties

Abstract

Two new N₂O₃ donor ligands N-(3-methoxysalicylidene)-N′-(salicylidene)-1,3-propanediamine (H₂L²) and N-(3-methoxysalicylidene)-N′-(α-methylsalicylidene)-1,3-propanediamine (H₂L³) and their Cu(II) complexes have been synthesized. Using these complexes and another Cu-complex with one asymmetric N₂O₂ donor ligand N-(α-methylsalicylidene)-N′-(salicylidene)-1,3-propanediamine (H₂L¹) as metalloligands, four new heterometallic Cu(II)–Mn(II) complexes [(CuL¹)₂Mn₂Cl₄]·3CH₃OH (1), [(CuL¹)₂MnCl₂]·2CH₃CN (2), [CuL²MnCl₂]·H₂O (3) and [CuL³MnCl₂] (4) have been synthesized with MnCl₂·4H₂O. The tetranuclear (1) and trinuclear (2) complexes were prepared by varying the ratio of the metalloligand [CuL¹] and MnCl₂ whereas dinuclear complexes 3 and 4 are the sole products irrespective of the metalloligand : MnCl₂ ratio. All the complexes 1–4 were structurally characterized by single crystal X-ray diffraction. The tetranuclear (Cu^II₂Mn^II₂) structure of 1 is formed by the dimerization of phenoxido bridged Cu^IIMn^II units whereas the bent Cu^II₂Mn^II trinuclear species 2 is formed by the coordination of two metalloligands (CuL¹) to Mn(II) via a diphenoxido bridge. Complexes 3 and 4 possess a similar dinuclear Cu^IIMn^II structure in which two phenoxido groups form a bridge between the two metal centres. The variable temperature dc magnetic susceptibility measurements reveal that the Cu(II) and Mn(II) ions are antiferromagnetically coupled in all the complexes, 1–4. The values of exchange coupling constants (J_Mn–Cu) are −45.54, −39.66, −71.54 and −48.40 cm⁻¹ for complexes 1–4, respectively. A DFT study of all the complexes has also been performed to rationalize the experimental results of magnetic measurements.