High-spin tetranuclear MnII2MnIV2clusters with unique Mn(ii)–Mn(iv) magnetic exchange: synthesis, structures and magnetism

Abstract

Reactions of N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine (H₄edte) with MnCl₂·4H₂O or FeCl₃·6H₂O in MeOH or MeCN with different bases yield four butterfly-like tetranuclear clusters with fused defective dicubane M₄O₆ cores: [Mn^II₂Mn^IV₂(μ₄-Hedte)₂(thme)₂]·MeCN (1) (H₄edte = N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine, H₃thme = 1,1,1-tris(hydroxymethyl)ethane), [Mn^II₂Mn^IV₂(μ₄-Hedte)₂(thme)₂]·2MeOH (2), [Fe^III₄(μ₄-Hedte)₂(N₃)₆]·2MeCN (3) and [Fe^III₄(μ₄-edte)₂(N₃)₄(MeOH)₂] (4). Both 1 and 3 crystallize in the triclinic space groupP, while 2 and 4 crystallize in the monoclinic space groupP2₁/c and P2₁/n, respectively. The hexadentate Hedte³⁻ ligand in 1–3, and the edte⁴⁻ ligand in 4 acts in a similar μ₄:η¹:η¹:η¹:η²:η²:η³ coordination mode to bridge four metal ions into butterfly-like tetranuclear clusters with fused defective dicubane M₄O₆ cores. Magnetic studies show that 2 has the spin ground state S_T = 8 while 4 has the spin ground state S_T = 0. Within the Mn₄O₆cluster core of 2, both Mn(IV)⋯Mn(II) and Mn(II)⋯Mn(II) ferromagnetic interactions (JMn(IV_)⋯Mn(II) = +2.91 cm⁻¹ and JMn(II_)⋯Mn(II) = +7.94 cm⁻¹) occur contrary to the Fe₄O₆ core, where antiferromagnetic exchange exists (J_{aptical-Fe(III)⋯central-Fe(III)} = −15.4 cm⁻¹ and J_{central-Fe(III)⋯central-Fe(III)} = −4.5 cm⁻¹).