High-spin tetranuclear (Mn2Mn2IV)-Mn-II clusters with unique Mn(II)-Mn(IV) magnetic exchange: synthesis, structures and magnetism

Reactions of N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine (H(4)edte) with MnCl2 center dot 4H(2)O or FeCl3 center dot 6H(2)O in MeOH or MeCN with different bases yield four butterfly-like tetranuclear clusters with fused defective dicubane M4O6 cores: [(Mn2Mn2IV)-Mn-II(mu(4)-Hedte)(2)(thme)(2)]center dot MeCN (1) (H(4)edte = N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine, H(3)thme = 1,1,1-tris(hydroxymethyl)ethane), [(Mn2Mn2IV)-Mn-II(mu(4)-Hedte)(2)(thme)(2)]center dot 2MeOH (2), [Fe-4(III)(mu(4)-Hedte)(2)(N-3)(6)]center dot 2MeCN (3) and [Fe-4(III)(mu(4)-edte)(2)-(N-3)(4)(MeOH)(2)] (4). Both 1 and 3 crystallize in the triclinic space group P (1) over bar, while 2 and 4 crystallize in the monoclinic space group P2(1)/c and P2(1)/n, respectively. The hexadentate Hedte(3-) ligand in 1-3, and the edte(4-) ligand in 4 acts in a similar mu(4):eta(1):eta(1):eta(1):eta(2):eta(2):eta(3) 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 Mn4O6 cluster core of 2, both Mn(IV)(center dot center dot center dot) Mn(II) and Mn(II)... Mn(II) ferromagnetic interactions (J(Mn(IV)center dot center dot center dot Mn(II)) = +2.91 cm(-1) and J(Mn(II)center dot center dot center dot Mn(II)) = +7.94 cm(-1)) occur contrary to the Fe4O6 core, where antiferromagnetic exchange exists (J(aptical-Fe(III)center dot center dot center dot central-(Fe(III)) = -15.4 cm(-1) and J(central-Fe(III)center dot center dot center dot central-Fe) =-4.5 cm(-1)).