Rare tetranuclear mixed-valent [Mn(II)2Mn(IV)2] clusters as building blocks for extended networks

We report the synthesis of a series of mixed valence Mn(II/IV) tetranuclear clusters [Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(EtOH)(6)Br(2)]Br(2) (), [Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(H(2)O)(2)Cl(4)].2EtOH.H(2)O (.2EtOH.H(2)O), [Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(heedH(2))(2)](ClO(4))(4) (), [Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(MeCN)(2)(H(2)O)(2)(bpy)(2)](ClO(4))(4) () and [Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(bpy)(2)Br(4)].2MeOH (.2MeOH). Clusters are constructed from the tripodal ligand N,N-bis(2-hydroxyethyl)ethylene diamine (heedH(2)) and represent rare examples of tetranuclear Mn clusters possessing the linear trans zig-zag topology, being the first Mn(II/IV) mixed-valent clusters of this type. The molecular clusters can then be used as building blocks in tandem with the (linear) linker dicyanamide ([N(CN)(2)](-), dca(-)) for the formation of a novel extended network {[Mn(II)(2)Mn(IV)(2)O(2)(heed)(2)(H(2)O)(2)(MeOH)(2)(dca)(2)]Br(2)}(n) (), which exhibits a rare form of the 2D herring bone topology.     

Hydrocarbon oxidation by Bis-mu-oxo manganese dimers: electron transfer,hydride transfer,and hydrogen atom transfer mechanisms

Described here are oxidations of alkylaromatic compounds by dimanganese mu-oxo and mu-hydroxo dimers [(phen)(2)Mn(IV)(mu-O)(2)Mn(IV)(phen)(2)](4+) ([Mn(2)(O)(2)](4+)), [(phen)(2)Mn(IV)(mu-O)(2)Mn(III)(phen)(2)](3+) ([Mn(2)(O)(2)](3+)), and [(phen)(2)Mn(III)(mu-O)(mu-OH)Mn(III)(phen)(2)](3+) ([Mn(2)(O)(OH)](3+)). Dihydroanthracene, xanthene, and fluorene are oxidized by [Mn(2)(O)(2)](3+) to give anthracene, bixanthenyl, and bifluorenyl, respectively. The manganese product is the bis(hydroxide) dimer, [(phen)(2)Mn(III)(mu-OH)(2)Mn(II)(phen)(2)](3+) ([Mn(2)(OH)(2)](3+)). Global analysis of the UV/vis spectral kinetic data shows a consecutive reaction with buildup and decay of [Mn(2)(O)(OH)](3+) as an intermediate. The kinetics and products indicate a mechanism of hydrogen atom transfers from the substrates to oxo groups of [Mn(2)(O)(2)](3+) and [Mn(2)(O)(OH)](3+). [Mn(2)(O)(2)](4+) is a much stronger oxidant, converting toluene to tolyl-phenylmethanes and naphthalene to binaphthyl. Kinetic and mechanistic data indicate a mechanism of initial preequilibrium electron transfer for p-methoxytoluene and naphthalenes because, for instance, the reactions are inhibited by addition of [Mn(2)(O)(2)](3+). The oxidation of toluene by [Mn(2)(O)(2)](4+), however, is not inhibited by [Mn(2)(O)(2)](3+). Oxidation of a mixture of C(6)H(5)CH(3) and C(6)H(5)CD(3) shows a kinetic isotope effect of 4.3 +/- 0.8, consistent with C-H bond cleavage in the rate-determining step. The data indicate a mechanism of initial hydride transfer from toluene to [Mn(2)(O)(2)](4+). Thus, oxidations by manganese oxo dimers occur by three different mechanisms: hydrogen atom transfer, electron transfer, and hydride transfer. The thermodynamics of e(-), H(*), and H(-) transfers have been determined from redox potential and pK(a) measurements. For a particular oxidant and a particular substrate, the choice of mechanism is influenced both by the thermochemistry and by the intrinsic barriers. Rate constants for hydrogen atom abstraction by [Mn(2)(O)(2)](3+) and [Mn(2)(O)(OH)](3+) are consistent with their 79 and 75 kcal mol(-)(1) affinities for H(*). In the oxidation of p-methoxytoluene by [Mn(2)(O)(2)](4+), hydride transfer is thermochemically 24 kcal mol(-)(1) more facile than electron transfer; yet the latter mechanism is preferred. Thus, electron transfer has a substantially smaller intrinsic barrier than does hydride transfer in this system.     

Coordination chemistry of the soluble metal oxide analogue [Mo5O13(OCH3)4(NO)]3- with manganese carbonyl species

The reactions of neutral or cationic manganese carbonyl species towards the oxo-nitrosyl complex [Na(MeOH)[Mo(5)O(13)(OCH(3))(4)(NO)]](2-) have been investigated in various conditions. This system provides an unique opportunity for probing the basic reactions involved in the preparation of solid oxide-supported heterogeneous catalysts, that is, mobility of transition-metal species at the surface and dissolution-precipitation of the support. Under nitrogen and in the dark, the reaction of in situ generated fac-[Mn(CO)(3)](+) species with (nBu(4)N)(2)[Na(MeOH)-[Mo(5)O(13)(OMe)(4)(NO)]] in MeOH yields (nBu(4)N)(2)[Mn(CO)(3)(H(2)O)[Mo(5)O(13)(OMe)(4)(NO)]] at room temperature, while (nBu(4)N)(3)[Na[Mo(5)O(13)(OMe)(4)(NO)](2)[Mn(CO)(3)](2)] is obtained under reflux. The former transforms into the latter under reflux in methanol in the presence of sodium bromide; this involves the migration of the fac-[Mn(CO)(3)](+) moiety from a basal kappa(2)O coordination site to a lateral kappa(3)O site. Oxidation and decarbonylation of manganese carbonyl species as well as degradation of the oxonitrosyl starting material and reaggregation of oxo(methoxo)molybdenum fragments occur in non-deareated MeOH, and both (nBu(4)N)(4)[Mn(H(2)O)(2)[Mo(5)O(16)(OMe)(2)](2)[Mn(CO)(3)](2)] and (nBu(4)N)(4)[Mn(H(2)O)(2)[Mo(5)O(13)(OMe)(4)(NO)](2)] as well as (nBu(4)N)(2)[MnBr[Mo(5)O(13)(OMe)(4)(NO)]] have been obtained in this way. The rhenium analogue (nBu(4)N)(2)[Re(CO)(3)(H(2)O)[Mo(5)O(13)(OMe)(4)(NO)]] has also been synthesized. The crystal structures of (nBu(4)N)(2)[Re(CO)(3)(H(2)O)[Mo(5)O(13)(OMe)(4)(NO)]], (nBu(4)N)(3)[Na[Mo(5)O(13)(OMe)(4)(NO)](2)[Mn(CO)(3)](2)], (nBu(4)N)(4)[Mn(H(2)O)(2)[Mo(5)O(16)(OMe)(2)](2)[Mn(CO)(3)](2)], (nBu(4)N)(4)[Mn(H(2)O)(2)[Mo(5)O(13)(OMe)(4)(NO)](2)] and (nBu(4)N)(2)[MnBr[Mo(5)O(13)(OMe)(4)(NO)]] have been determined.     

New mixed-valent Mn clusters from the use of N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine (edteH4): Mn3, Mn4, Mn6, and Mn10

The syntheses, crystal structures, and magnetochemical characterization are reported for the new mixed-valent Mn clusters [Mn(2)(II)Mn(III)(O(2)CMe)(2)(edteH(2))(2)](ClO(4)) (1), [Mn(II)(2)Mn(III)(2)(edteH(2))(2)(hmp)(2)Cl(2)](Mn(II)Cl(4)) (2), [Mn(III)(6)O(2)(O(2)CBu(t))(6)(edteH)(2)(N(3))(2)] (3), [Na(2)Mn(III)(8)Mn(II)(2)O(4)(OMe)(2)(O(2)CEt)(6)(edte)(2)(N(3))(6)] (4), and (NEt(4))(2)[Mn(8)(III)Mn(2)(II)O(4)(OH)(2)-(O(2)CEt)(6)(edte)(2)(N(3))(6)](5), where edteH(4) is N,N,N',N'-tetrakis-(2-hydroxyethyl)ethylenediamine and hmpH is 2-(hydroxymethyl)pyridine. 1-5 resulted from a systematic exploration of the effect of different Mn sources, carboxylates, the presence of azide, and other conditions, on the Mn/edteH(4) reaction system. The core of 1 consists of a linear Mn(II)Mn(III)Mn(II) unit, whereas that of 2 is a planar Mn(4) rhombus within a [Mn(II)(2)Mn(III)(2)(μ(3)-OR)(2)] incomplete-dicubane unit. The core of 3 comprises a central [Mn(III)(4)(OR)(2)] incomplete-dicubane on either side of which is edge-fused a triangular [Mn(III)(3)(μ(3)-O)] unit. The cores of 4 and 5 are similar and consist of a central [Mn(II)(2)Mn(III)(2)(μ(3)-OR)(2)] incomplete-dicubane on either side of which is edge-fused a distorted [Mn(II)Mn(III)(3)(μ(3)-O)(2)(μ(3)-OR)(2)] cubane unit. Variable-temperature, solid-state direct current (dc) and alternating current (ac) magnetization studies were carried out on 1-5 in the 5.0-300 K range, and they established the complexes to have ground state spin values of S = 3 for 1, S = 9 for 2, and S = 4 for 3. The study of 3 provided an interesting caveat of potential pitfalls from particularly low-lying excited states. For 4 and 5, the ground state is in the S = 0-4 range, but its identification is precluded by a high density of low-lying excited states.     

Hexametallic manganese clusters with bulky derivatised salicylaldoximes

The reaction of Mn(ClO(4))(2)·6H(2)O with Ph-saoH(2) (Ph-saoH(2) = 2-hydroxybenzophenone oxime) in MeCN in the presence of sodium propionate forms the complex [Mn(III)(6)O(2)(Ph-sao)(6)(prop)(2)(MeCN)(2)]·5.27MeCN (1·5.27MeCN) (prop = propionate). Repeating the same reaction in EtOH produces the complex [Mn(III)(6)O(2)(Ph-sao)(6)(prop)(2)(EtOH)(4)] (2). Complexes 1 and 2 may be considered as structural isomers, since they display the same metallic core but different coordination modes of the propionate ligands; bridging in 1 and terminal in 2. Performing similar reactions and switching from sodium propionate to sodium adamantane-carboxylate (NaO(2)C-ada) and sodium pivalate (Napiv) in the presence of NEt(4)OH yields the complexes [Mn(III)(6)O(2)(Ph-sao)(6)(O(2)C-ada)(2)(MeOH)(4)] (3) and [Mn(III)(6)O(2)(Ph-sao)(6)(piv)(2)(EtOH)(4)]·0.5Et(2)O (4·0.5Et(2)O), respectively. All four complexes contain the same {Mn(III)(3)O(Ph-sao)(3)} building block. Variable temperature magnetic susceptibility and magnetization studies show that all complexes possess an S = 4 ground-state.     

A new modification of an old framework: Hofmann layers with unusual tetracyanidometallate groups

Cyanidometallate complexes are highly versatile building units for the generation of functional porous materials. Here we report five new pillared Hofmann layer compounds incorporating the tetracyanidometallates [MoO(CN)(4)](2-) and [MnN(CN)(4)](2-). These metalloligands, which are new to this class of materials, have been combined with divalent 1st-row transition metals to produce Hofmann layers that are linked into three-dimensional frameworks by ditopic bridging dipyridyls. We report the structures and anomalous thermal expansion properties of five new materials: [Mn(H(2)O)(bpy)(?){MoO(CN)(4)(bpy)(?)}]·2H(2)O (1), [Mn(H(2)O)(bpy)(?){MnN(CN)(4)(bpy)(?)}]·2H(2)O (2), [Fe(H(2)O)(bpy)(?){MnN(CN)(4)(bpy)(?)}]·2H(2)O (3), [Co(H(2)O)(bpy)(?){MnN(CN)(4)(bpy)(?)}]·2H(2)O (4) and [{Mn(H(2)O)(2)}(?){Mn(bpa)(2)}(?){MoO(CN)(4)(bpa)(?)}]·MeOH (5), (where bpy = 4,4'-bipyridine and bpa = 4,4'-bipyridylacetylene).     

Mn(II) Coordination Polymers Based on Bi-, Tri-, and Tetranuclear and Polymeric Chain Building Units: Crystal Structures and Magnetic Properties

Five new Mn(II) coordination polymers, namely [Mn(2)(tbip)(2)(bix)] (1), [Mn(3)(tbip)(3)(bix)(2)] (2), [Mn(3)(tbip)(2)(Htbip)(2)(bib)(2)]·4H(2)O (3), [Mn(4)(tbip)(4)(bbp)(2)(H(2)O)(2)] (4), and [Mn(4)(tbip)(4)(bip)]·2H(2)O (5), were prepared by hydrothermal reactions of Mn(II) acetate with H(2)tbip (5-tert-butyl isophthalic acid) in the presence of different di-imidazolyl coligands (bix =1,4-bis(imidazol-1-ylmethyl)benzene, bib =1,4-bis(imidazol) butane, bbp =1,3-bis(benzimidazol)propane, bip =1,3-bis(imidazol)propane). All complexes were characterized by elemental analysis, IR spectra, thermogravimetric analysis, single-crystal X-ray crystallography, and powder X-ray diffraction. Single crystal X-ray studies show that these coordination polymers contain homometallic clusters varying from dimeric, trimeric, and tetrameric motifs to polymeric chains depending upon the coligands used. Complex 1 has a 3D 6-connected polycatenane network with dinuclear [Mn(2)O(2)] secondary building units. Complex 2 possesses a 3D 8-connected structure with trinuclear [Mn(3)(COO)(6)] units. Complex 3 shows a 3D pcu net based on trinuclear [Mn(3)(COO)(6)] clusters as nodes. Complex 4 features a 3D 8-connected structure constructed from the distorted square-grid tetranuclear [Mn(4)(μ(2)-COO)(8)(μ(2)-H(2)O)] units. Complex 5 shows a 3D (4,5,6)-connected net containing 1D μ-O/μ-COO alternately bridged chains. Magnetic susceptibility measurements indicate that complexes 1 and 3-5 show weak antiferromagnetic interactions between the adjacent Mn(II) ions, whereas 2 is a three-spin center homometallic ferromagnetic system.     

Unusual structural types in manganese cluster chemistry from the use of N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine: Mn8, Mn12, and Mn20 Clusters

The syntheses, crystal structures, and magnetochemical characterization are reported for three new mixed-valent Mn clusters [Mn(8)O(3)(OH)(OMe)(O(2)CPh)7(edte)(edteH(2))](2)CPh) (1), [Mn(12)O(4)(OH)(2)(edte)(4)C(l6)(H(2)O)(2)] (2), and [Mn(20)O(8)(OH)(4)(O(2)CMe)(6)(edte)(6)](ClO(4))(2) (3) (edteH(4) = (HOCH(2)CH(2))(2)NCH(2)CH(2)N(CH(2)CH(2)OH)(2) = N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine). The reaction of edteH(4) with Mn(O(2)CPh)(2), MnCl(2), or Mn(O(2)CMe)(2) gives 1, 2, and 3, respectively, which all possess unprecedented core topologies. The core of 1 comprises two edge-sharing [Mn(4)O(4)] cubanes connected to an additional Mn ion by a micro(3)-OH- ion and two alkoxide arms of edteH(22-). The core of 2 consists of a [Mn(12)(micro(4-)O)(4)](24+) unit with S4 symmetry. The core of 3 consists of six fused [Mn(4)O(4)] cubanes in a 3 x 2 arrangement and linked to three additional Mn atoms at both ends. Variable-temperature, solid-state dc and ac magnetization (M) studies were carried out on complexes 1-3 in the 5.0-300 K range. Fitting of the obtained M/Nmicro(B) vs H/T data by matrix diagonalization and including only axial zero-field splitting (ZFS) gave ground-state spin (S) and axial ZFS parameter (D) of S = 8, D = -0.30 cm-1 for 1, S = 7, D = -0.16 cm-1 for 2, and S = 8, D = -0.16 cm-1 for 3. The combined work demonstrates that four hydroxyethyl arms on an ethylenediamine backbone can generate novel Mn structural types not accessible with other alcohol-based ligands.     

Bridging nitrate groups in [Mn(4)O(3)(NO(3))(O(2)CMe)(3)(R(2)dbm)(3)] (R = H, Et) and [Mn(4)O(2)(NO(3))(O(2)CEt)(6)(bpy)(2)](ClO(4)): acidolysis routes to tetranuclear manganese carboxylate complexes

New synthesis procedures are described to tetranuclear manganese carboxylate complexes containing the [Mn(4)O(2)](8+) or [Mn(4)O(3)X](6+) (X(-) = MeCO(2)(-), F(-), Cl(-), Br(-), NO(3)(-)) core. These involve acidolysis reactions of [Mn(4)O(3)(O(2)CMe)(4)(dbm)(3)] (1; dbm is the anion of dibenzoylmethane) or [Mn(4)O(2)(O(2)CEt)(6)(dbm)(2)] (8) with HX (X(-) = F(-), Cl(-), Br(-), NO(3)(-)); high-yield routes to 1 and 8 are also described. The X(-) = NO(3)(-) complexes [Mn(4)O(3)(NO(3))(O(2)CR)(3)(R'(2)dbm)(3)] (R = Me, R' = H (6); R = Me, R' = Et (7); R = Et, R' = H (12)) represent the first synthesis of the [Mn(4)O(3)(NO(3))](6+) core, which contains an unusual eta(1):mu(3)-NO(3)(-) group. Treatment of known [Mn(4)O(2)(O(2)CEt)(7)(bpy)(2)](ClO(4)) with HNO(3) gives [Mn(4)O(2)(NO(3))(O(2)CEt)(6)(bpy)(2)](ClO(4)) (15) containing a eta(1):eta(1):mu-NO(3)(-) group bridging the two body Mn(III) ions of the [Mn(4)O(2)](8+) butterfly core. Complex 7 x 4CH(2)Cl(2) crystallizes in space group P2(1)2(1)2(1) with (at -168 degrees C) a = 21.110(3) A, b = 22.183(3) A, c = 15.958(2) A, Z = 4, and V = 7472.4(3) A(3). Complex 15 x (3)/(2)CH(2)Cl(2) crystallizes in space group P2(1)/c with (at -165 degrees C) a = 26.025(4) A, b = 13.488(2) A, c = 32.102(6) A, beta = 97.27(1) degrees, Z = 8, and V = 11178(5) A(3). Complex 7 contains a [Mn(4)(mu(3)-O)(3)(mu(3)-NO(3))](6+) core (3Mn(III), Mn(IV)) as seen for previous [Mn(4)O(3)X](6+) complexes. Complex 15 contains a butterfly [Mn(4)(mu(3)-O)(2)](8+) core. (1)H NMR spectra have been recorded for all complexes reported in this work and the various resonances assigned. All complexes retain their structural integrity on dissolution in chloroform and dichloromethane. Magnetic susceptibility (chi(M)) data were collected on 12 in the 5-300 K range in a 10.0 kG (1 T) field. Fitting of the data to the theoretical chi(M) vs T expression appropriate for a [Mn(4)O(3)X](6+) complex of C(3)(v)() symmetry gave J(34) = -23.9 cm(-)(1), J(33) = 4.9 cm(-)(1), and g = 1.98, where J(34) and J(33) refer to the Mn(III)Mn(IV) and Mn(III)Mn(III) pairwise exchange interactions, respectively. The ground state of the molecule is S = 9/2, as found previously for other [Mn(4)O(3)X](6+) complexes. This was confirmed by magnetization data collected at various fields and temperatures. Fitting of the data gave S = 9/2, D = -0.45 cm(-1), and g = 1.96, where D is the axial zero-field splitting parameter.     

A supramolecular aggregate of four exchange-biased single-molecule magnets

The reaction between 3-phenyl-1,5-bis(pyridin-2-yl)pentane-1,5-dione dioxime (pdpdH(2)) and triangular [Mn(III)(3)O(O(2)CMe)(py)(3)](ClO(4)) (1) affords [Mn(12)O(4)(O(2)CMe)(12)(pdpd)(6))](ClO(4))(4) (3). Complex 3 has a rectangular shape and consists of four [Mn(III)(3)O](7+) triangular units linked covalently by the dioximate ligands into a supramolecular [Mn(3)](4) tetramer. Solid-state dc and ac magnetic susceptibility measurements revealed that [Mn(3)](4) contains four Mn(3) single-molecule magnets (SMMs), each with an S = 6 ground state. Magnetization versus dc-field sweeps on a single crystal gave hysteresis loops below 1 K that exhibited exchange-biased quantum tunneling of magnetization steps, confirming 3 to be a supramolecular aggregate of four weakly exchange-coupled SMM units.     

Structure and magnetic exchange in heterometallic 3d-3d transition metal triethanolamine clusters

Synthetic methods are described that have resulted in the formation of seven heterometallic complexes, all of which contain partially deprotonated forms of the ligand triethanolamine (teaH(3)). These compounds are [Mn(III)(4)Co(III)(2)Co(II)(2)O(2)(teaH(2))(2)(teaH)(0.82)(dea)(3.18)(O(2)CMe)(2)(OMe)(2)](BF(4))(2)(O(2)CMe)(2)·3.18MeOH·H(2)O (1), [Mn(II)(2)Mn(III)(2)Co(III)(2)(teaH)(4)(OMe)(2)(acac)(4)](NO(3))(2)·2MeOH (2), [Mn(III)(2)Ni(II)(4)(teaH)(4)(O(2)CMe)(6)]·2MeCN (3), [Mn(III)(2)Co(II)(2)(teaH)(2)(sal)(2)(acac)(2)(MeOH)(2)]·2MeOH (4), [Mn(II)(2)Fe(III)(2)(teaH)(2)(paa)(4)](NO(3))(2)·2MeOH·CH(2)Cl(2) (5), [Mn(II)Mn(III)(2)Co(III)(2)O(teaH)(2)(dea)(Iso)(OMe)(F)(2)(Phen)(2)](BF(4))(NO(3))·3MeOH (6) and [Mn(II)(2)Mn(III)Co(III)(2)(OH)(teaH)(3)(teaH(2))(acac)(3)](NO(3))(2)·3CH(2)Cl(2) (7). All of the compounds contain manganese, combined with 3d transition metal ions such as Fe, Co and Ni. The crystal structures are described and examples of 'rods', tetranuclear 'butterfly' and 'triangular' Mn(3) cluster motifs, flanked in some cases by diamagnetic cobalt(III) centres, are presented. Detailed DC and AC magnetic susceptibility and magnetization studies, combined with spin Hamiltonian analysis, have yielded J values and identified the spin ground states. In most cases, the energies of the low-lying excited states have also been obtained. The features of note include the 'inverse butterfly' spin arrangement in 2, 4 and 5. A S = 5/2 ground state occurs, for the first time, in the Mn(III)(2)Mn(II) triangular moiety within 6, the many other reported [Mn(3)O](6+) examples having S = ? or 3/2 ground states. Compound 7 provides the first example of a Mn(II)(2)Mn(III) triangle, here within a pentanuclear Mn(3)Co(2) cluster.     

New routes to high nuclearity clusters: fluoride-based octametallic and tridecametallic clusters of manganese

The reaction of MnF(3) with 5,6-dimethylbenzotriazole (Me(2)BTAH) gives the [Mn(III)(8)] complex [Mn(8)O(4)(OMe)(2)(Me(2)BTA)(6)F(8)(Me(2)BTAH)(MeOH)(8)] and the [Mn(IV)(3)Mn(III)(10)] complex [Mn(13)O(12)(Me(2)BTA)(12)F(6)(MeOH)(10)(H(2)O)(2)]. The octametallic species is an "intermediate" in the formation of the tridecametallic cluster.     

Single-molecule magnets: a new family of Mn(12) clusters of formula [Mn(12)O(8)X(4)(O(2)CPh)(8)L(6)

The reaction of (NBu(n)(4))[Mn(8)O(6)Cl(6)(O(2)CPh)(7)(H(2)O)(2)] (1) with 2-(hydroxymethyl)pyridine (hmpH) or 2-(hydroxyethyl)pyridine (hepH) gives the Mn(II)(2)Mn(III)(10) title compounds [Mn(12)O(8)Cl(4)(O(2)CPh)(8)(hmp)(6)] (2) and [Mn(12)O(8)Cl(4)(O(2)CPh)(8)(hep)(6)] (3), respectively, with X = Cl. Subsequent reaction of 3 with HBr affords the Br(-) analogue [Mn(12)O(8)Br(4)(O(2)CPh)(8)(hep)(6)] (4). Complexes 2.2Et(2)O.4CH(2)Cl(2), 3.7CH(2)Cl(2), and 4.2Et(2)O.1.4CH(2)Cl(2) crystallize in the triclinic space group P1, monoclinic space group C2/c, and tetragonal space group I4(1)/a, respectively. Complexes 2 and 3 represent a new structural type, possessing isomeric [Mn(III)(10)Mn(II)(2)O(16)Cl(2)] cores but with differing peripheral ligation. Complex 4 is essentially isostructural with 3. A magnetochemical investigation of complex 2 reveals an S = 6 or 7 ground state and frequency-dependent out-of-phase signals in ac susceptibility studies that establish it as a new class of single-molecule magnet. These signals occur at temperatures higher than those observed for all previously reported single-molecule magnets that are not derived from [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(x)]. A detailed investigation of forms of complex 2 with different solvation levels reveals that the magnetic properties of 2 are extremely sensitive to the latter, emphasizing the importance to the single-molecule magnet properties of interstitial solvent molecules in the samples. In contrast, complexes 3 and 4 are low-spin molecules with an S = 0 ground state.     

Aggregation of tetranuclear Mn building blocks with alkali ion. Syntheses, crystal structures and chemical behaviors of monomer, dimer and polymer containing [Mn4(mu3-O)2]8+ units

Aggregation of tetranuclear Mn(4)O(2) building blocks with alkali ion was studied. Several Mn(iii) complexes containing [Mn(4)O(2)(AcO)(7)(pyz)(2)](-) (pyz = pyrazinate) anion(s) were obtained from an assembly system containing Mn(ii), MnO(4)(-), HOAc and Hpyz (Napyz or Kpyz). These [Mn(4)O(2)](8+) complexes have monomeric (1 and 2), dimeric (4 and 5) and one-dimensional chain () structures of which alkali metal ion connects the Mn ions of adjacent [Mn(4)O(2)](8+) units through mu(1,1)- and mu(1,3)-carboxylate bridges. Complexes 2 or 3 were converted into [Mn(12)O(12)(AcO)(16)(H(2)O)(4)] in EtOH solution in the presence of HOAc. However, in MeOH solution, a coordination polymer [Mn(2)(HCOO)(4)(H(2)O)(4)](n) was obtained accompanying the oxidation of MeOH to become HCHO and HCOOH. Tracing the (1)H NMR spectra of 2 or 3 in CD(3)OD, the disappearance of the resonance signals in 3 h indicated the decomposition of the [Mn(4)O(2)](8+) cores. Complex 2 exhibits its proton NMR signals in CDCl(3) which are similar to those of its pic analogue but accompany downfield shift to various extents for all the corresponding signals. Variable-temperature magnetic susceptibilities of complexes 2-5 in the range 5-300 K were recorded and were fitted for an Mn(4)O(2) butterfly core, giving the fitting parameters J(bb) = -2.67 to -3.76 cm(-1) and J(wb) = -1.16 to -3.14 cm(-1). Small J values indicate weak antiferromagnetic coupling interactions of the Mn(iii) sites and the spin ground states are considered as S(T) = 0 based on the J(bb)/J(wb) ratio approximately 1 for these complexes. The ESR spectra were recorded for complex 2 in dual-mode at liquid-helium temperatures and no obvious signal could be found. The addition of p-cresol gives rise to the reduction of the [Mn(4)O(2)](8+), resulting in observable signals.     

Syntheses, structures, and magnetic properties of a family of tetra-, hexa-, and nonanuclear Mn/Ni heterometallic clusters

A family of Mn(III)/Ni(II) heterometallic clusters, [Mn(III)(4)Ni(II)(5)(OH)(4)(hmcH)(4)(pao)(8)Cl(2)]·5DMF (1·5DMF), [Mn(III)(3)Ni(II)(6)(N(3))(2)(pao)(10)(hmcH)(2)(OH)(4)]Br·2MeOH·9H(2)O (2·2MeOH·9H(2)O), [Mn(III)Ni(II)(5)(N(3))(4)(pao)(6)(paoH)(2)(OH)(2)](ClO(4))·MeOH·3H(2)O (3·MeOH·3H(2)O), and [Mn(III)(2)Ni(II)(2)(hmcH)(2)(pao)(4)(OMe)(2)(MeOH)(2)]·2H(2)O·6MeOH (4·2H(2)O·6MeOH) [paoH = pyridine-2-aldoxime, hmcH(3) = 2, 6-Bis(hydroxymethyl)-p-cresol], has been prepared by reactions of Mn(II) salts with [Ni(paoH)(2)Cl(2)], hmcH(3), and NEt(3) in the presence or absence of NaN(3) and characterized. Complex 1 has a Mn(III)(4)Ni(II)(5) topology which can be described as two corner-sharing [Mn(2)Ni(2)O(2)] butterfly units bridged to an outer Mn atom and a Ni atom through alkoxide groups. Complex 2 has a Mn(III)(3)Ni(II)(6) topology that is similar to that of 1 but with two corner-sharing [Mn(2)Ni(2)O(2)] units of 1 replaced with [Mn(3)NiO(2)] and [MnNi(3)O(2)] units as well as the outer Mn atom of 1 substituted by a Ni atom. 1 and 2 represent the largest 3d heterometal/oxime clusters and the biggest Mn(III)Ni(II) clusters discovered to date. Complex 3 possesses a [MnNi(5)(μ-N(3))(2)(μ-OH)(2)](9+) core, whose topology is observed for the first time in a discrete molecule. Careful examination of the structures of 1-3 indicates that the Mn/Ni ratios of the complexes are likely associated with the presence of the different coligands hmcH(2-) and/or N(3)(-). Complex 4 has a Mn(III)(2)Ni(II)(2) defective double-cubane topology. Variable-temperature, solid-state dc and ac magnetization studies were carried out on complexes 1-4. Fitting of the obtained M/(Nμ(B)) vs H/T data gave S = 5, g = 1.94, and D = -0.38 cm(-1) for 1 and S = 3, g = 2.05, and D = -0.86 cm(-1) for 3. The ground state for 2 was determined from ac data, which indicated an S = 5 ground state. For 4, the pairwise exchange interactions were determined by fitting the susceptibility data vs T based on a 3-J model. Complex 1 exhibits out-of-phase ac susceptibility signals, indicating it may be a SMM.     

Binuclear manganese compounds of potential biological significance. Part 2. Mechanistic study of hydrogen peroxide disproportionation by dimanganese complexes: the two oxygen atoms of the peroxide end up in a dioxo intermediate

The dimanganese(II,II) complexes 1a [Mn(2)(L)(OAc)(2)(CH(3)OH)](ClO(4)) and 1b [Mn(2)(L)(OBz)(2)(H(2)O)](ClO(4)), where HL is the unsymmetrical phenol ligand 2-(bis-(2-pyridylmethyl)aminomethyl)-6-((2-pyridylmethyl)(benzyl)aminomethyl)-4-methylphenol, react with hydrogen peroxide in acetonitrile solution. The disproportionation reaction was monitored by electrospray ionization mass spectrometry (ESI-MS) and EPR and UV-visible spectroscopies. Extensive EPR studies have shown that a species (2) exhibiting a 16-line spectrum at g approximately 2 persists during catalysis. ESI-MS experiments conducted similarly during catalysis associate 2a with a peak at 729 (791 for 2b) corresponding to the formula [Mn(III)Mn(IV)(L)(O)(2)(OAc)](+) ([Mn(III)Mn(IV)(L)(O)(2)(OBz)](+) for 2b). At the end of the reaction, it is partly replaced by a species (3) possessing a broad unfeatured signal at g approximately 2. ESI-MS associates 3a with a peak at 713 (775 for 3b) corresponding to the formula [Mn(II)Mn(III)(L)(O)(OAc)](+) ([Mn(II)Mn(III)(L)(O)(OBz)](+) for 3b). In the presence of H(2)(18)O, these two peaks move to 733 and to 715 indicating the presence of two and one oxo ligands, respectively. When H(2)(18)O(2) is used, 2a and 3a are labeled showing that the oxo ligands come from H(2)O(2). Interestingly, when an equimolar mixture of H(2)O(2) and H(2)(18)O(2) is used, only unlabeled and doubly labeled 2a/b are formed, showing that its two oxo ligands come from the same H(2)O(2) molecule. All these experiments lead to attribute the formula [Mn(III)Mn(IV)(L)(O)(2)(OAc)](+) to 2a and to 3a the formula [Mn(II)Mn(III)(L)(O)(OAc)](+). Freeze-quench/EPR experiments revealed that 2a appears at 500 ms and that another species with a 6-line spectrum is formed transiently at ca. 100 ms. 2a was prepared by reaction of 1a with tert-butyl hydroperoxide as shown by EPR and UV-visible spectroscopies and ESI-MS experiments. Its structure was studied by X-ray absorption experiments which revealed the presence of two or three O atoms at 1.87 A and three or two N/O atoms at 2.14 A. In addition one N atom was found at a longer distance (2.3 A) and one Mn at 2.63 A. 2a can be one-electron oxidized at E(1/2) = 0.91 V(NHE) (DeltaE(1/2) = 0.08 V) leading to its Mn(IV)Mn(IV) analogue. The formation of 2a from 1a was monitored by UV-visible and X-ray absorption spectroscopies. Both concur to show that an intermediate Mn(II)Mn(III) species, resembling 4a [Mn(2)(L)(OAc)(2)(H(2)O)](ClO(4))(2), the one-electron-oxidized form of 1a, is formed initially and transforms into 2a. The structures of the active intermediates 2 and 3 are discussed in light of their spectroscopic properties, and potential mechanisms are considered and discussed in the context of the biological reaction.     

Mn8 and Mn16 clusters from the use of 2-(hydroxymethyl)pyridine, and comparison with the products from bulkier chelates: a new high nuclearity single-molecule magnet

The synthesis, crystal structures, and magnetochemical characterization of two new Mn clusters [Mn(8)O(2)(O(2)CPh)(10)(hmp)(4)(MeOH)(2)] (1; 6Mn(II), 2Mn(III)) and [Mn(16)O(8)(OH)(2)(O(2)CPh)(12)(hmp)(10)(H(2)O)(2)](O(2)CPh)(2) (2; 6Mn(II), 10Mn(III)) are reported. They were obtained from the use of 2-(hydroxymethyl)pyridine (hmpH) under the same reaction conditions but differing in the presence or absence of added base. Thus, the reaction of hmpH with Mn(O(2)CPh)(2) in CH(2)Cl(2)/MeOH led to isolation of octanuclear complex 1, whereas the analogous reaction in the presence of NEt(3) gave hexadecanuclear complex 2. Complexes 1 and 2 possess either very rare or unprecedented core structures that are related to each other: that of 1 can be described as a linked pair of incomplete [Mn(4)O(3)] cubanes, while that of 2 consists of a linked pair of complete [Mn(4)O(4)] cubanes, on either side of which is attached a tetrahedral [Mn(4)(μ(4)-O)] unit. Solid-state direct current (dc) and alternating current (ac) magnetic susceptibility measurements on 1 and 2 establish that they possess S = 5 and 8 ground states, respectively. Complex 2 exhibits frequency-dependent out-of-phase (χ(M)") ac susceptibility signals at temperatures below 3 K suggestive of a single-molecule magnet (SMM). Magnetization versus applied dc field sweeps on single crystals of 2·10MeOH down to 0.04 K exhibited hysteresis, confirming 2 to be a new SMM. Comparison of the structure of 2 (Mn(16)) with Mn(12) or Mn(6) clusters previously obtained under the same reaction conditions but with two Me or two Ph groups, respectively, added next to the alkoxide O atom of hmp(-) indicate their influence on the nuclearity and structure of the products as being due to the overall bulk of the chelate plus the decreased ability of the O atom to bridge.     

Dodecanuclear manganese(III) phosphonates with cage structures

Treatments of Mn(O(2)CR)(2) (R = Me, Ph) with NBu(4)MnO(4) in CH(3)CN or CH(3)CN/CH(2)Cl(2) in the presence of acetic acid, delta(1)-cyclohexenephosphonic acid (C(6)H(9)PO(3)H(2)), and 2,2'-bipyridine or 1,10-phenanthroline result in three novel dodecamanganese(III) clusters [Mn(12)O(8)(O(2)CMe)(6)(O(3)PC(6)H(9))(7)(bipy)(3)] (1), [Mn(12)O(8)(O(2)CPh)(6)(O(3)PC(6)H(9))(7)(bipy)(3)] (2), and [Mn(12)O(8)(O(2)CPh)(6)(O(3)PC(6)H(9))(7)(phen)(3)] (3). They have a similar Mn(12) core of [Mn(III)(12)(mu(4)-O)(3)(mu(3)-O)(5)(mu-O(3)P)(3)] with a new type of topologic structure. Solid-state dc magnetic susceptibility measurements of complexes 1-3 reveal that dominant antiferromagnetic interactions are propagated between the magnetic centers. The ac magnetic measurements suggest an S = 2 ground state for compounds 1 and 3 and an S = 3 ground state for compound 2.     

High turnover catalysis of water oxidation by Mn(II) complexes of monoanionic pentadentate ligands

Capillary electrophoresis (CE) and electrospray ionisation (ESI) mass spectra of aqueous solutions of manganese(II) complexes of the monoanions of the pentadentate ligands N-methyl-N'-carboxymethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine (mcbpen(-)) and N-benzyl-N'-carboxymethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine (bcbpen(-)), show the presence of a mixture of closely related Mn(II) species, assigned to the mono, di-, tri- and poly-cationic complexes [Mn(II)(L)(H(2)O)](n)(n+), L = mcbpen(-) or bcbpen(-) with n = 1, 2, 3, etc. In solution, these complexes are reversibly oxidized by tert-butyl hydrogen peroxide (TBHP), (NH(4))(2)[Ce(NO(3))(6)], Ce(ClO(4))(4), oxone and [Ru(bipy)(3)](3+) to form metastable (t(?) = min to h) higher valent (hydr)oxide species, showing a collective maximum absorbance at 430 nm. The same species can be produced by [Ru(bipy)(3)](2+)-mediated photooxidization in the presence of an electron acceptor. TBHP oxidation of the complexes, in large excesses of the TBHP, is concurrent with an O(2) evolution with turnovers of up to 1.5 × 10(4) mol of O(2) per mol of [Mn] and calculated rate constants from two series of experiments of 0.039 and 0.026 mol[O(2)] s(-1) M(-2). A 1:1 reaction of TBHP with [Mn] is rate determining and the resultant species is proposed to be the mononuclear, catalytically competent, [Mn(IV)(O)(mcbpen)](+). At very close m/z values [Mn(III)(OH)(mcbpen)](+), [Mn(2)(III/IV)(O)(2)(mcbpen)(2)](+) and [Mn(IV)(2)(O)(2)(mcbpen)(2)](2+) are detected by ESI MS and CE when the concentration of TBHP is comparable to or lower than that of [Mn]. These are conditions that occur post catalysis and these species are derived from [Mn(IV)(O)(mcbpen)](+) through condensation reactions.