New Structural Types of Mn sub(16) 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
• Subjects: Agglomeration; Approximation; Clusters; Magnetization; Magnets; Nitrates; Splitting; Topology
• ISSN: 0020-1669
• DOI: 10.1021/acs.inorgchem.5b01553

Two new Mn sub(16) clusters are reported: [Mn sub(16)O sub(10)(OH) sub(3)(OMe) sub(8)(O sub(2)CPhBu super(t)) sub(17)(MeOH)d5 (2) and [Mn sub(16)O sub(16)(OMe) sub(6)(O sub(2)CPh) sub(12)(NO sub(3))4(MeOH) sub(2)(H sub(2)) sub(4)] (3). The complexes were obtained by reductive aggregation of MnO sub(4) super(-) in CH sub(2)Cl sub(2)/MeOH, and oxidation of Mn super(II) and preformed (N super(n)Bu sub(4)) [Mn4 super(III)O sub(2)(O sub(2)CPh) sub(9)(H sub(2)O)] with Ce super(IV), respectively. The core of 2 has a Mn sub(16) super(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 x 3 Mn sub(6) super(IV) planar grid held within a nonplanar Mn sub(10) super(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 super(-1), g = 1.98(3) for 2 and S = 8, D = -0.22(1) cm super(-1), g = 1.99(2) for 3, where D is the axial zero-field splitting parameter. The ac in-phase ( chi sub(M)'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 ( chi sub(M)") signals revealed that both complexes are new single-molecule magnets (SMMs). Fits of the ac data gave U sub(eff) = 49.7(1) K and T sub(0) = 4.32 x 10 super(-9) s for 2 and U sub(eff) [approximate] 14.0 + or - 2 cm super(-1) and T sub(0) [approximate] 3.2 + or - 0.5 x 10 super(-8) s for 3, where U sub(eff) is the effective barrier to magnetization relaxation and T sub(0) is the pre-exponential factor. Thus, complexes 2 and 3 are two new members of a growing family of Mn sub(16) clusters, and two new examples of high-nuclearity SMMs, with the U sub(eff) for 2 approaching the value for the prototypical SMM family, [Mn sub(12)O sub(12)(O sub( 2)CR) sub(16)(H sub(2)O ) sub(4)].