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Unusual Structural Types in Manganese Cluster Chemistry from the Use of N,N,N‘,N‘-Tetrakis(2-hydroxyethyl)ethylenediamine:  Mn8, Mn12, and Mn20 Clusters

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posted on 21.01.2008, 00:00 by Rashmi Bagai, Khalil A. Abboud, George Christou
The syntheses, crystal structures, and magnetochemical characterization are reported for three new mixed-valent Mn clusters [Mn8O3(OH)(OMe)(O2CPh)7(edte)(edteH2)](O2CPh) (1), [Mn12O4(OH)2(edte)4Cl6(H2O)2] (2), and [Mn20O8(OH)4(O2CMe)6(edte)6](ClO4)2 (3) (edteH4 = (HOCH2CH2)2NCH2CH2N(CH2CH2OH)2 = N,N,N‘,N‘-tetrakis(2-hydroxyethyl)ethylenediamine). The reaction of edteH4 with Mn(O2CPh)2, MnCl2, or Mn(O2CMe)2 gives 1, 2, and 3, respectively, which all possess unprecedented core topologies. The core of 1 comprises two edge-sharing [Mn4O4] cubanes connected to an additional Mn ion by a μ3-OH- ion and two alkoxide arms of edteH22-. The core of 2 consists of a [Mn12(μ4-O)4]24+ unit with S4 symmetry. The core of 3 consists of six fused [Mn4O4] cubanes in a 3 × 2 arrangement and linked to three additional Mn atoms at both ends. Variable-temperature, solid-state dc and ac magnetization (M) studies were carried out on complexes 13 in the 5.0−300 K range. Fitting of the obtained M/NμB vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave ground-state spin (S) and axial ZFS parameter (D) of S = 8, D = −0.30 cm-1 for 1, S = 7, D = −0.16 cm-1 for 2, and S = 8, D = −0.16 cm-1 for 3. The combined work demonstrates that four hydroxyethyl arms on an ethylenediamine backbone can generate novel Mn structural types not accessible with other alcohol-based ligands.