A [Mn₃₂] Double‐Decker Wheel

Abstract

Polynuclear clusters of paramagnetic 3d metal ions continue to attract significant interest because of their intriguing geometrical characteristics (large size, high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties. Such complexes often combine large and sometimes abnormally large spin ground states with easyaxis-type magnetic anisotropy, resulting in a significant barrier to magnetization relaxation. [1][2][3] Thus, at sufficiently low temperatures they function as single-domain magnetic particles displaying magnetization hysteresis and quantum tunneling of the magnetization (QTM). [3, 4] Such singlemolecule magnets (SMMs) represent a molecular approach to nanoscale magnetic materials with potential applications in information storage and molecular spintronics. [5] SMMs with nuclearities up to 84 and structural topologies as diverse as (amongst others) dimers, triangles, cubanes, tetrahedra, icosahedra, and wheels are now known. [1][2][3]6] The latter of these have always attracted intense interest, partly because of their inherent structural beauty, but also because they represent model systems for the study of one-dimensional magnetism, spin frustration, and quantum effects and are promising candidates for use as qubits in quantum computation. [7] Homo-and heterometallic molecular wheels are commonly encountered in 3d cluster chemistry, [8][9][10][11][12][13][14][15] and in general they fall into two distinct structural types. By far the most common are single-stranded wheels, which simply describe linked monometallic units. [8, 9] Multiple-stranded wheels are less common and encompass either 1) wheels built from repeating metal clusters, [10] or 2) multiple-layer wheels, that is, complexes that consist of two or more linked parallel wheels. Those of structural type (2) are extremely rare, being restricted to [V 12 ], [11] [Mn 10 ], [12] [Mn 16 ], [13] and [Cu 12 ] [14] double-deckers, [15] none of which display SMM behavior. Herein we report a beautiful new mixed-valent [Mn 32 ] double-decker wheel, which is the highest-nuclearity cluster possessing this topology, and show that it has a large spin ground state and displays SMM behavior with the largest effective barrier to magnetization relaxation (U eff % 44.5 K) for any molecular wheel.The reaction of MnBr 2 ·4 H 2 O, NaO 2 CMe, 2-phenyl-1,2propanediol (Ph-pdH 2 ), and 2-hydroxyacetophenone oxime (Me-saoH 2 ) in a 1:1:1:1 molar ratio in MeCN leads to the isolation of [Mn 32 (m 4 -O) 8 (m 3 -OH) 6 (Me-sao) 14 (O 2 CMe) 18 Br 8 -(H 2 O) 10 ](OH) 2 (1) in 30 % yield after approximately 1 week. The diol does not appear in the final product, but its presence in the reaction mixture is essential, since reactions in its absence lead to the formation of a known [Mn 7 ] cluster. [16] The structure of the cation of 1 [17] reveals it to be a centrosymmetric, mixed-valent [Mn II 18 Mn III 14 ] doubledecker wheel (Figure 1 a), consisting of two linked, parallel [Mn II 7 Mn III 7 ] crown-shaped wheels (Figure 1 b, c) th...

Combining Complementary Ligands into one Framework for the Construction of a Ferromagnetically Coupled [MnIII12] Wheel

“…This is especially fruitful if the ligands have a track record of success in making Mn clusters in their own right, and if the respective building blocks are complementary. Indeed our initial attempts at employing phenolic oximes and diols in the same reactions has proved to be somewhat successful 8. An alternative approach would be to combine the phenolic oxime and diol moieties within the same ligand framework, and herein, we report the synthesis, structure and magnetic properties of the dodecametallic wheel [Mn III 12 (OMe) 16 (L) 4 (O 2 CCMe 3 ) 4 (MeOH) 4 ] ( 1 ) constructed by using the new pro‐ligand H 4 L (Figure 1, left).…”

A Database of Topological Representations of Polynuclear Nickel Compounds

“…It is well established that wheels have attracted intense interest, partly as a result of their inherent structural beauty, but also because they represent model systems for the study of 1D magnetism, spin frustration, and quantum effects, and they are promising candidates for use as qubits in quantum computation 50. With our database, it is very easy to identify some simple Ni wheels by filtering the database with the types 2M5‐1 , 2M6‐1 , 2M8‐1 , 2M10‐1 , 2M11‐1 , and 2M12‐1 .…”

“…[50] With our database, it is very easy to identify some simple Ni wheels by filtering the database with the types 2M5-1, 2M6-1, 2M8-1, 2M10-1, 2M11-1, and 2M12-1. [50] With our database, it is very easy to identify some simple Ni wheels by filtering the database with the types 2M5-1, 2M6-1, 2M8-1, 2M10-1, 2M11-1, and 2M12-1.…”

Synthetic Factors Determining the Curvature and Nuclearity of the Giant Mn70 and Mn84 Clusters with a Torus Structure of ∼4 nm Diameter

“…Such giant molecules can be thought of as mesoscale materials lying at the interface between the quantum and classical realms of nanomagnetism and thus as candidates for study of potentially new physical phenomena, especially if they are SMMs, but this area is currently underdeveloped . To date, over fifty giant paramagnetic clusters based on 3d and 3d/4f metal ions have been reported, illustrating a panoply of molecular architectures and magnetic properties, yet among them only a few are SMMs. − Among these are the giant Mn 70 and Mn 84 SMMs with a torus-like structure of ∼4 nm diameter that are the largest homometallic 3d SMMs to date. They are also part of a limited family of giant homometallic molecules of any metal with a torus-like structure, spanning Pd 72 and Pd 84 clusters and the Mo 154 , Mo 176 , and Mo 248 polyoxometalates .…”