Constructing clusters with enhanced magnetic properties by assembling and distorting Mn3 building blocks

Abstract

The reaction of Mn(ClO₄)₂·6H₂O with Naphth-saoH₂ (Naphth-saoH₂ = 2-hydroxy-1-napthaldoxime) in pyridine (py) forms the complex [Mn^III₃O(Naphth-sao)₃(py)₃](ClO₄)·0.5py (1·0.5py) in very good yields. Reaction of 1 with NaO₂CPh in EtOH produces the complex [Mn^III₆O₂(Naphth-sao)₆(O₂CPh)₂(EtOH)₆]·[Mn^III₆O₂(Naphth-sao)₆(O₂CPh)₂(EtOH)₄]·2.5Et₂O·0.5H₂O (2·2.5Et₂O·0.5H₂O). Further reaction of complex 2 with 1 equivalent of both NaN₃ and Mn(ClO₄)₂·6H₂O in MeOH produces the complex [Mn^II₂Mn^III₆O₂(Naphth-sao)₆(N₃)₆(MeOH)₈]·10MeOH (3·10MeOH) that displays an S≈ 0 ground state. Ligand substitution of Naphth-saoH₂ with Me-saoH₂ in CH₂Cl₂–MeOH for the latter complex (Me-saoH₂= 2-hydroxyphenylethanone oxime) forms the complex [Mn^II₂Mn^III₆O₂(Me-sao)₆(N₃)₆(MeOH)₈]·10MeOH (4·10MeOH) that displays an S = 7 ground state with U_eff= 44.6 K. In all four complexes the main building block is the triangular {Mn^III₃O(R-sao)₃} unit (R = Naphth for 1, 2 and 3; R = Me for 4). The ligand substitution in 3 triggers a structural distortion in the [Mn₆] sub-core as observed by the increased (Mn–N–O–Mn) torsion angles in 4, switching the interactions from antiferro- to ferromagnetic, dramatically changing the ground-state of the octanuclear complexes from S = 0 to 7.