Unexpected diversity and novel features within a family of new azide-bridged MnII complexes of pyridyl/imineligands

Abstract

A family of tetradentate ligands, [N,N′-bis(pyridine-2-yl)]ethane-1,2-diamine (L1), [N,N′-bis(pyridine-2-yl)]propane-1,3-diamine (L2) and [N,N′-bis(pyridine-2-yl)]butane-1,4-diamine (L3) has been prepared. These ligands differ only in the number of CH₂ groups separating two pyridyl/imine moieties, however, in reactions with Mn^II and N⁻₃ salts, they produce structurally very diverse solids; [Mn₂(L1)₃(N₃)]_n(ClO₄)_3n (1), [Mn₂(L2)₂(N₃)₂](PF₆)₂ (2) and [Mn₂(L3)(N₃)₂]_n(ClO₄)_2n (3). Complexes 1, 2 and 3 consist of azido-bridged magnetically dilute Mn₂ pairs, arranged as 1-D, discrete and 2-D arrays, respectively. In these materials, the connection between Mn centers within the dinuclear entities occurs through mono-1,3-N⁻₃, bis-1,3-N⁻₃ and bis-1,1-N⁻₃ bridges, respectively, for 1, 2 and 3. Bulk magnetic measurements reveal that the coupling within such units is antiferromagnetic (J = −1.8 cm⁻¹, 1; J = −4.8 cm⁻¹, 2) and ferromagnetic (J = +1.45 cm⁻¹, 3), depending on whether the N⁻₃ binding mode is end-to-end (EE) or end-on (EO). The reported values are given according to the convention H = −2JS₁S₂ for the spin-Hamiltonian.