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

Abstract

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 (NnBu4)[Mn4IIIO2(O2CPh)9(H2O)] with CeIV, respectively. The core of 2 has a Mn16III 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 Mn6IV planar grid held within a nonplanar Mn10III 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 Ueff = 49.7(1) K and τ0 = 4.32 × 10–9 s for 2 and Ueff ≈ 14.0 ± 2 cm–1 and τ0 ≈ 3.2 ± 0.5 × 10–8 s for 3, where Ueff 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 Ueff for 2 approaching the value for the prototypical SMM family, [Mn12O12(O2CR)16(H2O)4].

Long-Range Ferromagnetic Exchange Interactions Mediated by Mn–CeIV–Mn Superexchange Involving Empty 4f Orbitals

“…This is "reductive aggregation," which we originally developed in homometallic Mn chemistry and which involves the methanolysis-driven reduction and concomitant aggregation of MnO 4 − ions in MeOH in the presence of excess carboxylic acid. This proved to be a rich source of new Mn x (x usually is 12 or 16) clusters, the first being [Mn 12 O 12 (OMe) 2 (O 2 CPh) 16 (H 2 O) 2 ] 2− , 13 a distinct structural variant of the prototypical SMM [Mn 12 O 12 (O 2 CMe) 16 (H 2 O) 4 ]. 14 Reductive aggregation employs a single high oxidation source of Mn, and the MeOH has a multifunctional role as the solvent, the reducing agent, and a source of alkoxide ligands.…”

“…Reductive aggregation employs a single high oxidation source of Mn, and the MeOH has a multifunctional role as the solvent, the reducing agent, and a source of alkoxide ligands. Depending on the carboxylic acid employed, a number of new structural types of Mn 12 and Mn 16 clusters were obtained, many of them new SMMs, including an unusual and highly symmetrical “W-shaped” [Mn 16 O 16 (OMe) 6 (O 2 CPh) 12 (NO 3 ) 4 (MeOH) 2 (H 2 O) 4 ] …”

Mn3 Single-Molecule Magnets and Mn6/Mn9 Clusters from the Use of Methyl 2-Pyridyl Ketone Oxime in Manganese Phosphinate and Phosphonate Chemistry

“…Developing methods for the synthesis and modification of coordination-cluster SMMs has been one of our group’s interests, including from comproportionation, reductive aggregation, alcoholysis, and others. The work described herein is relevant to previous investigations of the effect of substituting the carboxylate ligands in Mn/O/RCO 2 – clusters with “pseudocarboxylates” (i.e., having an XO 2 – unit that can bridge like a carboxylate, e.g., in the common η 1 :η 1 :μ mode), either pre- or postsynthetically.…”

In-Depth Magnetic Characterization of a [2 × 2] Mn(III) Square Grid Using SQUID Magnetometry, Inelastic Neutron Scattering, and High-Field Electron Paramagnetic Resonance Spectroscopy

“…Toward this direction, a plethora of systems have been synthesized from simple to highly complex ones − in order to study and model the magnetic properties of Mn­(III). DC magnetization measurements (magnetic susceptibility and magnetization) performed on a SQUID magnetometer are probably the most widely used and usually efficient methods to probe magnetic properties.…”

“…Herein we report a comprehensive structural, magnetic, and spectroscopic study of a tetranuclear Mn­(III) system with a [2 × 2] grid-like core topology, [ Mn 4 ; general formula: Mn 4 L 4 (DMF) 4 ·2DMF, H 3 L: ( E )-3-((2-hydroxyphenyl)­imino)­methyl)­benzene-1,2-diol (Figure ), DMF: N , N -dimethylformamide]. Complexes with grid topologies of various nuclearities have been synthesized and used extensively as models for magnetic properties; − nevertheless, most of the examples are either purely Mn­(II) species or mixed Mn­(II)/Mn­(III) complexes with just a few containing only Mn­(III) ions. , SQUID magnetometry has been performed on Mn 4 where antiferromagnetic behavior was observed. However, the complexity of the magnetic behavior did not allow the interpretation of the data based on a unique reasonable magnetic model without inevitably resulting in overparametrization.…”