New Structural Types of Mn16 Single-Molecule Magnets: W‑Shaped Topology from Reductive Aggregation

• Published in: Inorganic chemistry 2015-09, Vol.54 (18), p.9127-9137
• Main Authors: Thuijs, Annaliese E, King, Philippa, Abboud, Khalil A, Christou, George
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.5b01553

Two new Mn16 clusters are reported: [Mn16O­10­(OH)3­(OMe)8(O2CPhBut)17(MeOH)5] (2) and [Mn16O16(OMe)6­(O2CPh)12­(NO3)4(MeOH)2(H2O)4] (3). The complexes were obtained by reductive aggregation of MnO4 – in CH2Cl2/MeOH, and oxidation of MnII and preformed (N n Bu4)­[Mn4 IIIO2(O2CPh)9(H2O)] with CeIV, respectively. The core of 2 has a Mn16 III core with an unusual 1:2:3:4:3:2:1 layer structure and a W-shaped pleated topology, whereas 3 contains a central 2 × 3 Mn6 IV planar grid held within a nonplanar Mn10 III loop and is a rare example of a complex with nitrate ions bridging like carboxylate ions. Variable-temperature, solid-state dc susceptibility, and ac susceptibility studies reveal that 2 and 3 possess S = 12 and S = 8 ground states, respectively. Fits of dc magnetization data collected over a temperature range of 1.8–4.0 K and a magnetization range of 0.1–4 T were fit to give S = 12, D = −0.16(2) cm–1, g = 1.98(3) for 2 and S = 8, D = −0.22(1) cm–1, g = 1.99(2) for 3, where D is the axial zero-field splitting parameter. The ac in-phase (χM ′ T) susceptibility below 15 K confirmed the ground-state spin values of 2 and 3, as determined from dc data, and the appearance of frequency-dependent out-of-phase (χM ″) signals revealed that both complexes are new single-molecule magnets (SMMs). Fits of the ac data gave U eff = 49.7(1) K and τ0 = 4.32 × 10–9 s for 2 and U eff ≈ 14.0 ± 2 cm–1 and τ0 ≈ 3.2 ± 0.5 × 10–8 s for 3, where U eff is the effective barrier to magnetization relaxation and τ0 is the pre-exponential factor. Thus, complexes 2 and 3 are two new members of a growing family of Mn16 clusters, and two new examples of high-nuclearity SMMs, with the U eff for 2 approaching the value for the prototypical SMM family, [Mn12O12(O2CR)16(H2O)4].