Synthesis, Structure and Magnetic Properties of a Linear Trinuclear Mn（II） Complex with a Multifunctional Group Ligand

By use of a new ligand containing both salicylic acid moiety and salicylaldehyde Schiff base moiety, 5-(2-hydroxybenzylideneamino)-2-hydroxybenzoic acid (H3L), a linear trinuclear Mn(II) complex was prepared. This complex crystallizes in triclinic, space group P1 with a = 12.0196(7), b = 13.7440(13), c = 15.7554(14) , α = 111.529(3), β = 96.691(2), γ = 94.802(2)o, C96H100Mn3N6O32, Mr = 2014.64, V = 2382.0(3) 3, Z = 1, μ = 0.478, Dc = 1.404 g/cm3, F(000) = 1049, R = 0.0554 and wR = 0.1610 for 8973 observed reflections (I 2σ(I)). The complex consists of a trinuclear cluster and two solvate ethanol molecules. Three linearly disposed Mn atoms, with an inversion center on the central one, are bridged by six carboxylate groups from six bulky mono-anionic ligands (H2L–), and the octahedral coordination spheres for each of the metal centers are thus formed, with the aid of additional ligation of two small molecules (ethanol and water) to both ends. The magnetic properties of the title complex are also included in this paper.     

Large pressure-induced red shift of the luminescence band originating from nonstacked square-planar [Pt(SCN)4]2- in a novel trimetallic complex

Luminescence of the novel trimetallic complex {Pt(SCN)2[(mu-SCN)Mn(NCS)(bipy)2]2} originates from a d-d transition of the square-planar [Pt(SCN)4]2- moiety. The band maximum shows a red shift of -99 cm(-1) kbar(-1) under external pressure up to 32 kbar at room temperature. This red shift is comparable to values for crystals where Pt-Pt interaction between stacked complexes is enhanced by pressure, but the crystal structure for the trimetallic complex shows that no metal-metal interaction can occur.     

Making "wheels" and "cubes" from triangles

[Mn(IV)Mn(II)3] triangular units directed by the presence of tripodal alcohols self-assemble in the presence of azide and acetate ligands to form either a [Mn24] "wheel" or a [Mn32] "cube".     

A novel carboxylate-free ferromagnetic trinuclear mu(3)-oxo-manganese(III) complex with distorted pentagonal-bipyramidal metal centers

In methanol, the reaction of Mn(ClO(4))(2).6H(2)O and 1,2-bis(biacetylmonoximeimino)ethane (H(2)bamen) in the presence of triethylamine affords a trinuclear complex having the formula [Mn(3)(mu(3)-O)(mu(3)-bamen)(3)]ClO(4).2H(2)O. The structure of this complex shows a symmetric planar central [Mn(III)(3)(mu(3)-O)] unit coordinated to three hexadentate bridging (via oximate groups) ligands. The N(4)O(3) coordination sphere around each metal center is very close to pentagonal-bipyramidal. A cyclic voltammogram of the complex displays two reversible and an irreversible response due to Mn(III)(3) --> Mn(III)(2)Mn(IV), Mn(III)(2)Mn(IV) --> Mn(III)Mn(IV)(2), and Mn(III)Mn(IV)(2) --> Mn(IV)(3) oxidation processes, respectively. Cryomagnetic data reveal that the complex is ferromagnetic.     

Dioxo-bridged dinuclear manganese(III) and -(IV) complexes of pyridyl donor tripod ligands: combined effects of steric substitution and chelate ring size variations on structural,spectroscopic, and electrochemical properties

The syntheses and structural, spectral, and electrochemical characterization of the dioxo-bridged dinuclear Mn(III) complexes [LMn(mo-O)(2)MnL](ClO(4))(2), of the tripodal ligands tris(6-methyl-2-pyridylmethyl)amine (L(1)) and bis(6-methyl-2-pyridylmethyl)(2-(2-pyridyl)ethyl)amine (L(2)), and the Mn(II) complex of bis(2-(2-pyridyl)ethyl)(6-methyl-2-pyridylmethyl)amine (L(3)) are described. Addition of aqueous H(2)O(2) to methanol solutions of the Mn(II) complexes of L(1) and L(2) produced green solutions in a fast reaction from which subsequently precipitated brown solids of the dioxo-bridged dinuclear complexes 1 and 2, respectively, which have the general formula [LMn(III)(mu-O)(2)Mn(III)L](ClO(4))(2). Addition of 30% aqueous H(2)O(2) to the methanol solution of the Mn(II) complex of L(3) ([Mn(II)L(3)(CH(3)CN)(H(2)O)](ClO(4))(2) (3)) showed a very sluggish change gradually precipitating an insoluble black gummy solid, but no dioxo-bridged manganese complex is produced. By contrast, the Mn(II) complex of the ligand bis(2-(2-pyridyl)ethyl)(2-pyridylmethyl)amine (L(3a)) has been reported to react with aqueous H(2)O(2) to form the dioxo-bridged Mn(III)Mn(IV) complex. In cyclic voltammetric experiments in acetonitrile solution, complex 1 shows two reversible peaks at E(1/2) = 0.87 and 1.70 V (vs Ag/AgCl) assigned to the Mn(III)(2) <--> Mn(III)Mn(IV) and the Mn(III)Mn(IV) <--> Mn(IV)(2) processes, respectively. Complex 2 also shows two reversible peaks, one at E(1/2) = 0.78 V and a second peak at E(1/2) = 1.58 V (vs Ag/AgCl) assigned to the Mn(III)(2) <--> Mn(III)Mn(IV) and Mn(III)Mn(IV) <--> Mn(IV)(2) redox processes, respectively. These potentials are the highest so far observed for the dioxo-bridged dinuclear manganese complexes of the type of tripodal ligands used here. The bulk electrolytic oxidation of complexes 1 and 2, at a controlled anodic potential of 1.98 V (vs Ag/AgCl), produced the green Mn(IV)(2) complexes that have been spectrally characterized. The Mn(II) complex of L(3) shows a quasi reversible peak at an anodic potential of E(p,a) of 1.96 V (vs Ag/AgCl) assigned to the oxidation Mn(II) to Mn(III) complex. It is about 0.17 V higher than the E(p,a) of the Mn(II) complex of L(3a). The higher oxidation potential is attributable to the steric effect of the methyl substituent at the 6-position of the pyridyl donor of L(3).     

The Spectrophotometry Determination of Mn(III) in the Presence of Mn(IV)

Abstract

The spectra of complex of Mn(III) and Mn(IV) with pyrophosphoric acid are investigated. The molar absorption coefficient of the complex of Mn(III) with pyrophosphoric acid is 80.6/Mcm at 510nm which is close to that of Mn(IV), 110/Mcm, however, the molar absorption coefficient of the complex of Mn(HI) with pyrophosphoric acid is only 4.98/Mcm at 398nm which is much less than that of Mn(IV), 390/Mcm. Based on this absorbance difference between Mn(III) and Mn(IV) at wavelength 398nm and 510nm, a procedure of determination of Mn(III) in the presence of Mn(IV) has been developed.     

[Mn3O(O2CC6H5)6(C3H4N2)3]·C6H5CO2·0.5H2O的 合成、晶体结构及磁性质

Mn(O2CMe)2·4H2O、咪唑、苯甲酸和N(n-Bu)4MnO4在无水乙醇溶剂中反应,制备得到锰的三核μ3-O桥联配位化合物[Mn3O(O2CC6H5)6(C3H4N2)3]·C6H5CO2·0.5H2O.该配位化合物的X射线单晶衍射表明,其属于单斜晶系,空间群P21/C,晶胞参数：a=1.52832(19)nm,b=1.9722(2)nm,c=2.1023(3)nm,β=92.597(3)°,Z=4.变温磁化率(5～280K)研究表明,该配位化合物中3个锰离子在低温下存在弱的反铁磁性耦合,交换积分J=-2.34cm^-1。     

Single-molecule magnets: a large Mn30 molecular nanomagnet exhibiting quantum tunneling of magnetization

The largest single-molecule magnet (SMM) to date has been prepared and studied. Recrystallization of known [Mn(12)O(12)(O(2)CCH(2)Bu(t))(16)(H(2)O)(4)] (1; 8Mn(III), 4Mn(IV)) from CH(2)Cl(2)/MeNO(2) causes its conversion to [Mn(30)O(24)(OH)(8)(O(2)CCH(2)Bu(t))(32)(H(2)O)(2)(MeNO(2))(4)] (2; 3Mn(II), 26Mn(III), Mn(IV)). The structure of 2 consists of a central, near-linear [Mn(4)O(6)] backbone, to either side of which are attached two [Mn(13)O(9)(OH)(4)] units. Peripheral ligation around the resulting [Mn(30)O(24)(OH)(8)] core is by 32 Bu(t)CH(2)CO(2)(-), 2 H(2)O, and 4 MeNO(2) groups. The molecule has crystallographically imposed C(2) symmetry. Variable-temperature and -field magnetization (M) data were collected in the 1.8-4.0 K and 0.1-0.4 T ranges and fit by matrix diagonalization assuming only the ground state is occupied at these temperatures. The fit parameters were S = 5, D = -0.51 cm(-1) = -0.73 K, and g = 2.00, where D is the axial zero-field splitting parameter. AC susceptibility measurements in the 1.8-7.0 K range in a zero DC field and a 3.5 G AC field oscillating at frequencies in the 50-997 Hz range revealed a frequency-dependent out-of-phase (chi(M)') signal below 3 K, indicating 2 to be a single-molecule magnet (SMM), the largest yet obtained. Magnetization versus DC field sweeps show hysteresis loops but no clear steps characteristic of quantum tunneling of magnetization (QTM). However, magnetization decay data below 1 K were collected and used to construct an Arrhenius plot that revealed temperature-independent relaxation below 0.3 K. The fit of the thermally activated region above approximately 0.5 K gave U(eff)/k = 15 K, where U(eff) is the effective relaxation barrier. Resonant QTM was confirmed from the appearance of a "quantum hole" when the recent quantum hole digging method was employed. The combined results demonstrate that SMMs can be prepared that are significantly larger than any known to date and that this new, large Mn(30) complex still demonstrates quantum behavior.     

Models for the lower S states of photosystem II: a trinuclear mixed-valent MnII/MnIV/MnII complex

The trinuclear complex Mn(3)(pko)(4)(CH(3)O)(2)(SCN)(2).CH(3)OH, 1, where Hpko is 2,2'-dipyridylketonoxime, is a rare example of a complex simultaneously containing Mn(II) and Mn(IV). X-ray crystallography and XANES spectroscopy clearly distinguish the Mn(II)(2)Mn(IV) valence isomer from the more commonly observed Mn(III)(2)Mn(II) formulation. Fits to variable-temperature magnetic susceptibility data indicate that the Mn(II) and Mn(IV) are ferromagnetically coupled (J = +6.13 cm(-1)) and that 1 has an S = (13)/(2) ground state.     

Largest mixed transition metal/actinide cluster: a bimetallic Mn/Th complex with a [Mn10Th6O22(OH)2]18+ core

A high-nuclearity mixed transition metal/actinide complex has been prepared from the reaction of a Mn(III)4 complex with Th(NO3)4 in MeCN/MeOH. The complex [Th6Mn10O22(OH)2(O2CPh)16(NO3)2-(H2O)8] is the largest such complex to date and the first Th/Mn species. It is rich in oxide groups, which stabilize all of the metals in the high Th(IV) and Mn(IV) oxidation levels. Magnetic characterization establishes that the complex has an S = 3 ground-state spin value.     

Magnetic resonance and kinetic studies of the mechanism of membrane-bound sodium and potassium ion- activated adenosine triphosphatase.

EPR and water proton relaxation rate (1/T1) studies of partially (40%) and "fully" (90%) purified preparations of membrane-bound (Na+ + K+) activated ATPase from sheep kidney indicate one tight binding site for Mn2+ per enzyme dimer, with a dissociation constant (KD = 0.88 muM) in agreement with the kinetically determined activator constant, identifying this Mn2+-binding site as the active site of the ATPase. Competition studies indicate that Mg2+ binds at this site with a dissociation constant of 1 mM in agreement with its activator constant. Inorganic phosphate and methylphosphonate bind to the enzyme-Mn2+ complex with similar high affinities and decrease 1/T1 of water protons due to a decrease from four to three in the number of rapidly exchanging water protons in the coordination sphere of enzyme-bound Mn2+. The relative effectiveness of Na+ and K+ in facilitating ternary complex formation with HPO2-4 and CH3PO2-3 as a function of pH indicates that Na+ induces the phosphate monoanion to interact with enzyme-bound Mn2+. Thus protonation of an enzyme-bound phosphoryl group would convert a K+-binding site to a Na+-binding site. Dissociation constants for K+ and Na+, estimated from NMR titrations, agreed with kinetically determined activator constants of these ions consistent with binding to the active site. Parallel 32Pi-binding studies show negligible formation (less than 7%) of a covalent E-P complex under these conditions, indicating that the NMR method has detected an additional noncovalent intermediate in ion transport. Ouabain, which increases the extent of phosphorylation of the enzyme to 24% at pH 7.8 and to 106% at pH 6.1, produced further decreases in 1/T1 of water protons. Preliminary 31P- relaxation studies of CH3PO2-3 in the presence of ATPase and Mn2+ yield an Mn to P distance (6.9 +/- 0.5 A) suggesting a second sphere enzyme-Mn-ligand-CH3PO2-3 complex. Previous kinetic studies have shown that T1+ substitutes for K+ in the activation of the enzyme but competes with Na+ at higher levels. From the paramagnetic effect of Mn2+ at the active site on the enzyme on I/T1 of 205T1 bound at the Na+ site, a Mn2+ to T1+ distance of 4.0 +/- 0.1 A is calculated, suggesting the sharing of a common ligand atomy by Mn2+ and T1+ on the ATPase. Addition of Pi increases this distance to 5.4 A consistent with the insertion of P between Mn2+ and T1+. These results are consistent with a mechanism for the (Na+ + K+)-ATPase and for ion transport in which the ionization state of Pi at a single enzyme active site controls the binding and transport of Na+ and K+, and indicate that the transport site for monovalent cations is very near the catalytic site of the ATPase. Our mechanism also accounts for the order of magnitude weaker binding of Na+ compared to K+.     

Magnetic behavior control in niccolite structural metal formate frameworks [NH2(CH3)2][Fe(III)M(II)(HCOO)6] (M = Fe, Mn, and Co) by varying the divalent metal ions

By changing template cation but introducing trivalent iron ions in the known niccolite structural metal formate frameworks, three complexes formulated [NH(2)(CH(3))(2)][Fe(III)M(II)(HCOO)(6)] (M = Fe for 1, Mn for 2, and Co for 3) were synthesized and magnetically characterized. The variation in the compositions of the complexes leads to three different complexes: mixed-valent complex 1, heterometallic but with the same spin state complex 2, and heterometallic heterospin complex 3. The magnetic behaviors are closely related to the divalent metal ions used. Complex 1 exhibits negative magnetization assigned as Ne?el N-Type ferrimagnet, with an asymmetric magnetization reversal in the hysteresis loop, and complex 2 is an antiferromagnet with small spin canting (α(canting) ≈ 0.06° and T(canting) = 35 K), while complex 3 is a ferrimagnet with T(N) = 32 K.     

Oxidative atom-transfer to a trimanganese complex to form Mn6(μ6-E) (E = O, N) clusters featuring interstitial oxide and nitride functionalities

Utilizing a hexadentate ligand platform, a trinuclear manganese complex of the type ((H)L)Mn(3)(thf)(3) was synthesized and characterized ([(H)L](6-) = [MeC(CH(2)N(C(6)H(4)-o-NH))(3)](6-)). The pale-orange, formally divalent trimanganese complex rapidly reacts with O-atom transfer reagents to afford the μ(6)-oxo complex ((H)L)(2)Mn(6)(μ(6)-O)(NCMe)(4), where two trinuclear subunits bind the central O-atom and the ((H)L) ligands cooperatively bind both trinuclear subunits. The trimanganese complex ((H)L)Mn(3)(thf)(3) rapidly consumes inorganic azide ([N(3)]NBu(4)) to afford a dianionic hexanuclear nitride complex [((H)L)(2)Mn(6)(μ(6)-N)](NBu(4))(2), which subsequently can be oxidized with elemental iodine to ((H)L)(2)Mn(6)(μ(6)-N)(NCMe)(4). EPR and alkylation of the interstitial light atom substituent were used to distinguish the nitride from the oxo complex. The oxo and oxidized nitride complexes give rise to well-defined Mn(II) and Mn(III) sites, determined by bond valence summation, while the dianionic nitride shows a more symmetric complex, giving rise to indistinguishable ion oxidation states based on crystal structure bond metrics.     

A highly reactive mononuclear non-heme manganese(IV)-oxo complex that can activate the strong C-H bonds of alkanes

A mononuclear non-heme manganese(IV)-oxo complex has been synthesized and characterized using various spectroscopic methods. The Mn(IV)-oxo complex shows high reactivity in oxidation reactions, such as C-H bond activation, oxidations of olefins, alcohols, sulfides, and aromatic compounds, and N-dealkylation. In C-H bond activation, the Mn(IV)-oxo complex can activate C-H bonds as strong as those in cyclohexane. It is proposed that C-H bond activation by the non-heme Mn(IV)-oxo complex does not occur via an oxygen-rebound mechanism. The electrophilic character of the non-heme Mn(IV)-oxo complex is demonstrated by a large negative ρ value of -4.4 in the oxidation of para-substituted thioanisoles.     

Visible light-induced electron transfer from di-mu-oxo-bridged dinuclear Mn complexes to Cr centers in silica nanopores

The compound (bpy) 2Mn (III)(mu-O) 2Mn (IV)(bpy) 2, a structural model relevant for the photosynthetic water oxidation complex, was coupled to single Cr (VI) charge-transfer chromophores in the channels of the nanoporous oxide AlMCM-41. Mn K-edge EXAFS spectroscopy confirmed that the di-mu-oxo dinuclear Mn core of the complex is unaffected when loaded into the nanoscale pores. Observation of the 16-line EPR signal characteristic of Mn (III)(mu-O) 2Mn (IV) demonstrates that the majority of the loaded complexes retained their nascent oxidation state in the presence or absence of Cr (VI) centers. The FT-Raman spectrum upon visible light excitation of the Cr (VI)-O (II) --> Cr (V)-O (I) ligand-to-metal charge transfer reveals electron transfer from Mn (III)(mu-O) 2Mn (IV) (Mn-O stretch at 700 cm (-1)) to Cr (VI), resulting in the formation of Cr (V) and Mn (IV)(mu-O) 2Mn (IV) (Mn-O stretch at 645 cm (-1)). All initial and final states are directly observed by FT-Raman or EPR spectroscopy, and the assignments are corroborated by X-ray absorption spectroscopy measurements. The endoergic charge separation products (Delta E o = -0.6 V) remain after several minutes, which points to spatial separation of Cr (V) and Mn (IV)(mu-O) 2Mn (IV) as a consequence of hole (O (I)) hopping as a major contributing mechanism. This is the first observation of visible light-induced oxidation of a potential water oxidation complex by a metal charge-transfer pump in a nanoporous environment. These findings will allow for the assembly and photochemical characterization of well-defined transition metal molecular units, with the ultimate goal of performing endothermic, multielectron transformations that are coupled to visible light electron pumps in nanostructured scaffolds.     

离子液体功能化手性salen Mn(Ⅲ)配合物不对称催化仲醇氧化动力学拆分反应

采用共价键联法,将亲水性咪唑类离子液体结构引入手性salen Mn(Ⅲ)配合物的C5位,制备了离子液体功能化手性salen Mn(Ⅲ)配合物.傅里叶变换红外光谱、紫外光谱和旋光分析等结果表明,咪唑类离子液体结构已嫁接到手性salen Mn(Ⅲ)配合物结构中,且嫁接过程未破坏催化活性中心.在以PhI(OAc)2为氧化剂,H2O/CH2Cl2为溶剂的(+/-)-α-甲基苯甲醇不对称氧化动力学拆分反应中,该催化剂表现出比传统手性salen Mn(Ⅲ)催化剂更高的催化活性,仲醇的转化率达到63%以上,对映选择性为99%,拆分效率为18.3%.可通过调变溶剂实现催化剂的分离并重复使用3次以上.实验结果表明,亲水性咪唑离子液体可改善水相反应传质问题且有利于稳定催化活性中间体,从而提高催化活性及稳定性.     

Dimer-of-dimers model for the oxygen-evolving complex of photosystem II. Synthesis and properties of [MnIV4O5(terpy)4(H2O)2](ClO4)6

A dimer-of-dimers model compound for the oxygen-evolving complex of photosystem II, [[(H(2)O)(terpy)Mn(IV)(micro-O)(2)Mn(IV)(terpy)](2)(micro-O)](ClO(4))(6) (terpy = 2,2':6',2' '-terpyridine), has been prepared and characterized by X-ray crystallography and ESI-MS. Low pH was found to promote the disproportionation of [Mn(III/IV)(2)O(2)(terpy)(2)(OH(2))(2)](3+) to Mn(2+) and a Mn(IV/IV)(2)O(2)(terpy)(2) species; the latter complex slowly dimerizes to form the title complex. Protonation of a micro-oxo bridge is proposed to initiate the disproportionation, based on analogy with the [Mn(III/)(IV)(2)O(2)(bpy)(4)](3+) system.     

Magnetic structure of the large-spin Mn10 and Mn19 complexes: a theoretical complement to an experimental milestone

High-spin molecules have been proposed as candidates for the storage of information at the molecular level. The electronic structure of two complex magnetic molecular systems, Mn 10 and Mn 19, is characterized by means of a computational study based on density functional theory. All the exchange interactions in the recently reported Mn 19 complex with the highest known spin value of 83/2, and in its highly symmetric Mn 10 parent compound, are ferromagnetic. In these complexes, there are two kinds of ferromagnetic coupling: the first one corresponds to Mn (II)-Mn (III) interactions through a double mu 2-alkoxo-mu 4-oxo bridge where the high coordination number of the Mn (II) cations results in long Mn (II)-O bond distances, while the second one involves Mn (III)-Mn (III) interactions through mu 2-alkoxo-mu 3-eta (1):eta (1):eta (1) azido bridging ligands with long Mn (III)-N distances due to a Jahn-Teller effect.     

Generation of an isolable, monomeric manganese(V)-oxo complex from O2 and visible light

The direct conversion of a Mn(III) complex [(TBP(8)Cz)Mn(III) (1)] to a Mn(V)-oxo complex [(TBP(8)Cz)Mn(V)(O) (2)] with O(2) and visible light is reported. Complex 1 is also shown to function as an active photocatalyst for the oxidation of PPh(3) to OPPh(3). Mechanistic studies indicate that the photogeneration of 2 does not involve singlet oxygen but rather likely occurs via a free-radical mechanism upon photoactivation of 1.     

Synthesis, structure and magnetic properties of the first Mn(II)-Gd(III) heteronuclear complex

The synthesis and crystal structure of a novel pentanuclear Mn(II)-Gd(III) complex is reported; the magnetic measurement conclusively demonstrated anti-ferromagnetic behaviour between Mn(II) and Gd(III) for this complex.