Sheyi Wang

Manganese carboxylate clusters: From structural aesthetics to single-molecule magnets

Abstract An overview is provided of some recent developments in manganese carboxylatecluster chemistry. A variety of synthetic methodologies are described together with the structuresof the resultant products, which span metal nuclearities of 4 to 18 and oxidation states of II to IV,including mixed-valency. The spins of the ground states of these products are often large andsometimes abnormally large, and in certain cases when this is coupled to a sufficiently largemagnetoanisotropy, the clusters function as single-molecule magnets i.e., they can be magnetizedby an external magnetic field below a critical temperature. These complexes display hysteresis inmagnetization vs . magnetic field studies, and clear evidence for quantum tunnelling ofmagnetization. Such results establish single-molecule magnetism as a new magnetic phenomenon,and one that holds great promise for next-century technological applications.

[Mn3O(O2CPh)6(py)2]2(4,4′-bpy) and [Mn9O7(O2CC6H4-p-OMe)13 (4,4′-bpy)]2: new multinuclear manganese complexes

Abstract The synthesis, X-ray crystal structures and magnetic properties of two new types of dimers of multinuclear manganese aggregates are described. [Mn 3 O(O 2 CPh) 6 (py) 2 ] 2 (4,4′-bpy) is prepared from the reaction of the trinuclear starting material [Mn 3 O(O 2 CPh) 6 (py) 2 (H 2 O)] with 4,4′-bipyridine. This compound can be described as a dimer of trinuclear units and has been characterized crystallographically as part of a unit cell which also contains a monomeric, trinuclear species. Dimers of enneanuclear manganese complexes linked by two bifunctional units (4,4′-bipyridine or trans -1,2-bis(4-pyridylethene)) may be prepared from the tetranuclear starting material, (su0)Bu 4 N)[Mn 4 O 2 -(O 2 CR) 9 (H 2 O)], where R = Ph or C 6 H 4 - p -OMe. The new octadecanuclear complex [Mn 9 O 7 (O 2 CC 6 H 4 - p -OMe) 13 (4,4′-bpy)] 2 has been structurally characterized. This complex shows magnetic behavior which can be fit by considering only magnetic interactions within the individual Mn 9 O 7 units.

Covalent linkage of [Mn4O2(O2CPh)6(dbm)2] into a dimer and a one-dimensional polymer (dbmH = dibenzoylmethane)

Methods have been developed for covalently linking [Mn4O2(O2CPh)6(dbm)2]2(dbmH = dibenzoylmethane) units to give a dimer and a polymer; treatment of 2 with trans-1,2-bis(4-pyridyl)ethene (bpe) or 4,4′-bipyridine (4,4′-bpy) yields [Mn4O2(O2CPh)6(dbm)2(bpe)]24 and [Mn4O2(O2CPh)6(dbm)2(4,4′-bpy)]n5, respectively.

High Spin Molecules: A Structural and Magnetic Comparison of High Nuclearity Manganese Carboxylate Aggregates

Abstract A structural and magnetic comparison is presented for a number of high nuclearity, higher oxidation state manganese complexes with similar ligation environments. The complexes considered are hepta-, octa-, ennea-, deca-, and dodecanuclear and contain only MnIII, except for the dodecanuclear complexes, which are mixed valence (MnIII 8MnIV 4). The ground state spins of these complexes range from very low to very high, and while the dodecanuclear complexes exhibit unusual AC magnetic susceptibility behavior, none of the other complexes show such properties. Magnetic properties, as well as structural and preparative information, are discussed.

High nuclearity molecular species exhibiting spin frustration : fusion of two MnIII4O2 butterfly complexes to yield an intermediate spin ground state MnIII7O4 complex

The preparation and characterization of (NEt4)[Mn7O4(OAc)10(dbm)4]·3CH2Cl2·2C6H14(1·3CH2Cl2·2C6H14)(H dbm = dibenzoylmethane)are reported; the MnIII7O4 core of 1 consists of two Mn4O2 butterfly units fused together by sharing of one wing-tip manganese atom and it is shown using magnetization data that complex 1 has either an S= 3 or S= 4 ground state.

Bromide incorporation into a high-oxidation-state manganese aggregate, and reversible redox processes for the [Mn4O3X(OAc)3(dbm)3] (X =) Cl, Br) complexes

Treatment of [Mn4O2(OAc)6(py)2(dbm)2](dbmH = dibenzoylmethane) with either NBun4Br in hot MeCN or Me3SiBr in CH2Br2 leads to the 3MnIII, MnIV cubane complex [Mn4O3Br(OAc)3(dbm)3]3, the initial example of Br– bridging high-oxidation-state (III) Mn ions; in addition, 3 and its Cl– analogue display similar and reversible redox processes and similar magnetic exchange interactions, observations of significant biological relevance to the photosynthetic water-oxidation enzyme.