A Family of Mn₁₆ Single-Molecule Magnets from a Reductive Aggregation Route

Abstract

The synthesis and magnetic properties of three isostructural hexadecametallic manganese clusters [Mn(16)O(16)(OMe)(6)(O(2)CCH(2)Ph)(16)(MeOH)(6)] (1), [Mn(16)O(16)(OMe)(6)(O(2)CCH(2)Cl)(16)(MeOH)(6)] (2), and [Mn(16)O(16)(OMe)(6)(O(2)CCH(2)Br)(16)(MeOH)(6)] (3) are reported. The complexes were prepared by a reductive aggregation reaction involving phenylacetic acid, chloroacetic acid or bromoacetic acid, and NBu(n)()(4)MnO(4) in MeOH. Complex 1 crystallizes in the monoclinic space group C2/c and consists of 6 Mn(IV) and 10 Mn(III) ions held together by 14 mu(3)-O(2)(-), 2 mu-O(2)(-), 4 mu-MeO(-), and 2 mu-O(2)CCH(2)Ph(-) groups. The remaining 14 mu-O(2)CCH(2)Ph(-) ligands, 2 mu-MeO(-) groups, and 6 terminal MeOH molecules constitute the peripheral ligation in the complex. Variable-temperature, solid-state dc magnetic susceptibility measurements on 1-3 in the temperature range 5.0-300 K reveal that all three complexes are dominated by intramolecular antiferromagnetic exchange interactions. Low-lying excited states preclude an exact determination of the spin ground state for 1-3 by magnetization measurements. Alternating current susceptibility measurements at zero dc field in the temperature range 1.8-10 K and a 3.5 G ac field oscillating at frequencies in the 5-1488 Hz range display, at temperatures below 3 K, a nonzero, frequency-dependent chi(M)"signal for complexes 1-3, with the peak maxima lying at temperatures less than 1.8 K. Single-crystal magnetization versus dc field scans down to 0.04 K for complex 1 show hysteresis behavior at <1 K, establishing 1 as a new member of the SMM family. No clear steps characteristic of quantum tunneling of magnetization (QTM) were observed in the hysteresis loops.

A Mn6 Cluster inside a Mn10 Wheel: Characterization of a Mn16‐Oximate Complex Resulting from a Tetrazole‐2‐pyridylketoneoximate Ligand

“…The hexanuclear fragment, composed of the Mn(1), Mn(2), Mn(8) cations (and their symmetry equivalents), is linked to the wheel by means of six μ 4 ‐O and additional oximato bridges. The structure of 1 shows closely related fragments with the above‐described Mn III 10 Mn IV 6 complex,3,4 but in addition to the different manganese oxidation states, it shows a subunit of the inner defective cubane placed perpendicularly to the mean wheel plane, which generates an unprecedented Mn 16 core (Figure 2). It is remarkable that complex 1 , together with two Mn 16 complexes containing methyl‐2‐pyridylketoneoximate7 or 2,6‐diacetylpyridineoximate,8 exhibits the maximum nuclearity seen to date in complexes that have 2‐pyridyloxime ligands and is the largest Mn/2‐pyridyloximate complex containing azido bridges 9…”

“…In search of a SMM response, larger metallic wheels around in‐plane defective cubane fragments have been characterized,2–5 which form a beautiful family of related structures with the easy axis of the Mn III cations roughly aligned (Scheme ). These larger complexes exhibit lower spin ground states than Mn III 8 Mn IV 4 and, except for one of the Mn III 10 Mn IV 6 complexes,3 small magnetization reversal barriers2,4 or even no SMM response5 were reported.…”

Coordination Clusters of 3d-Metals That Behave as Single-Molecule Magnets (SMMs): Synthetic Routes and Strategies

“…The reaction of phenylacetic acid (PhCH 2 CO 2 H) with (Bu n 4 N)(MnO 4 ) in MeOH leads to a dark brown solution and isolation of [ O 16 (OMe) 6 (O 2 CCH 2 Ph) 16 (MeOH) 6 ] ( 20 ) (King et al, 2004 ), eqn. (18).…”

Recent Progress in the Realm of Homonuclear Ln6 Single molecule magnets: Structural Overview and Synthetic Approaches

“…Typically, the first category is represented by symmetric arrangement of the six metal centers to construct a metallic wheel/ring, while the other category is typified by the relatively more familiar combinations of interconnected triangles. Rather than distinguishing these SMM materials based on the symmetry-aspect, it seems more judicious to divide the entire regime of the reported hexanuclear SMMs into two more general broad classifications: First class being the homonuclear Ln 6 series where the metal centers are solely 4f-elements, whereas the second class comprises of the heteronuclear entities composed of both 3d-and 4f-metal centers (Randell et al, 2013;Boskovic et al, 2002;Brechin et al, 2002;King et al, 2004;Zheng et al, 2007;Manoli et al, 2007;Feng et al, 2010;Stamatatos et al, 2011;Nayak et al, 2010;Kotzabasaki et al, 2011;Yang et al, 2011;Costa et al, 2012;Charalambous et al, 2012;Chakraborty et al, 2012;Mukherjee et al, 2014). Hereafter, our discussion will revolve around the first class only.…”