Polynuclear Manganese Complexes Research Articles

Evaluation of Manganese Cubanoid Clusters for Water Oxidation Catalysis: From Well-Defined Molecular Coordination Complexes to Catalytically Active Amorphous Films.

With a view to developing multimetallic molecular catalysts that mimic the oxygen‐evolving catalyst (OEC) in Nature's photosystem II, the synthesis of various dicubanoid manganese clusters is described and their catalytic activity investigated for water oxidation in basic, aqueous solution. Pyridinemethanol‐based ligands are known to support polynuclear and cubanoid structures in manganese coordination chemistry. The chelators 2,6‐pyridinedimethanol (H2L1) and 6‐methyl‐2‐pyridinemethanol (HL2) were chosen to yield polynuclear manganese complexes; namely, the tetranuclear defective dicubanes [MnII 2MnIII 2(HL1)4(OAc)4(OMe)2] and [MnII 2MnIII 2(HL1)6(OAc)2] (OAc)2⋅2 H2O, as well as the octanuclear‐dicubanoid [MnII 6MnIII 2(L2)4(O)2(OAc)10(HOMe/OH2)2]⋅3MeOH⋅MeCN. In freshly prepared solutions, polynuclear species were detected by electrospray ionization mass spectrometry, whereas X‐band electron paramagnetic resonance studies in dilute, liquid solution suggested the presence of divalent mononuclear Mn species with g values of 2. However, the magnetochemical investigation of the complexes’ solutions by the Evans technique confirmed a haphazard combination of manganese coordination complexes, from mononuclear to polynuclear species. Subsequently, the newly synthesized and characterized manganese molecular complexes were employed as precursors to prepare electrode‐deposited films in a buffer‐free solution to evaluate and compare their stability and catalytic activity for water oxidation electrocatalysis.

Di-μ-benzoato-di-μ-ethano-lato-tetra-kis-[μ3-5-(hy-droxy-meth-yl)-2-methyl-4-(oxidometh-yl)pyridin-1-ium-3-olato]tetra-kis-[μ3-5-(hy-droxy-meth-yl)-2-methyl-4-(oxidometh-yl)pyridin-3-olato]di-μ3-oxido-hepta-manganese(II,III) ethanol octa-solvate.

Our work in the area of synthesis of polynuclear manganese complexes and their magnetic properties led to the synthesis and crystallization of the title compound, [Mn7(C8H9NO3)4(C8H10NO3)4(C2H5O)2(C7H5O2)2O2]·8C2H5OH. Herein, we report the molecular and crystal structure of the title compound, which was synthesized by the reaction of Mn(C6H5COO)2 with pyridoxine (PNH2, C8H11NO3) followed by the addition of tetra-methyl-ammonium hydroxide (TMAOH). The core of this centrosymmetric complex is a cage-like structure consisting of six MnIII ions and one MnII ion bound together through Mn-O bonds. The compound crystallizes in hydrogen-bonded layers formed by O-H⋯N hydrogen bonds involving the aromatic amine group of the ligand PN2- with the neighboring O atoms from the PNH- ligand. The crystal structure has large voids present in which highly disordered solvent mol-ecules (ethanol) sit. A solvent mask was calculated and 181 electrons were found in a volume of 843 Å3 in one void per triclinic unit cell. This is consistent with the presence of seven ethanol mol-ecules per formula unit, which accounts for 182 electrons per unit cell. Additionally, one ethanol mol-ecule was found to be ordered in the crystal.

Structural characterization and biological evaluation of polynuclear Mn(II) and Cd(II) complexes with 2,2-dimethyl-1,3-propanediamine-N,N,N’,N’-tetraacetate. The influence of ligand structure and counter cation on the complex nuclearity

New polynuclear manganese(II) and cadmium(II) complexes with 2,2-dimethyl-1,3-propanediamine-N,N,N’,N’-tetraacetato ligand (2,2-diMe-1,3-pdta), {Ba[M(2,2-diMe-1,3-pdta)].3H2O}n (M = Mn (1) or Cd (2)) were synthesized and characterized by IR spectroscopy and single-crystal X-ray diffraction analysis. In addition, complex 2 was characterized by solution 1H and 13C NMR spectroscopy. Crystallographic analysis showed that 2,2-diMe-1,3-pdta ligand is hexadentately coordinated to each M(II) ion through the two nitrogen and four carboxylate oxygen atoms, whereas the one of these oxygen atoms is also involved in coordination to the second M(II) ion of the dinuclear [M2(2,2-diMe-1,3-pdta)2]4− unit in polymeric structures. Moreover, three of four carboxylic groups of 2,2-diMe-1,3-pdta ligand are additionally bonded to four Ba(II) ions, in three distinctive bridging coordination modes. Each Ba(II) ion is surrounded by ten oxygen atoms, seven belonging to carboxylate groups of 2,2-diMe-1,3-pdta, and three belonging to water molecules. The coordination environment around Mn(II) and Cd(II) ions could be assigned as a face capped octahedron, while coordination polyhedron around Ba(II) ion in these two complexes was described as a distorted sphenocorona. The antimicrobial potential of complexes 1 and 2 and corresponding metal salts used for their synthesis was evaluated against different bacterial and Candida spp. Both complexes showed selective antifungal activity against the tested Candida spp. compared to the bacterial strains, with the minimal inhibitory concentration (MIC) values in the range 3.12 – 12.50 µM. Moreover, complex 1 caused the slightly decrease of hyphae length, while no significant influence on hyphal length of complex 2 was observed. With aim to assess the therapeutic profile of the complexes, their cytotoxicity was evaluated against the normal human lung fibroblast cell line (MRC-5).

Tetra- and dinuclear manganese complexes of xanthene-bridged O,N,O-Schiff bases with 3-hydroxypropyl or 2-hydroxybenzyl groups: ligand substitution at a triply bridging site

Complexation properties of U-shaped ligands, L1 and L2, which are Schiff bases of 5,5'-(9,9-dimethylxanthene-4,5-diyl)bis(salicylaldehyde) (H2xansal) with 3-amino-1-propanol or 2-hydroxybenzylamine, respectively, were investigated to construct polynuclear manganese complexes. In these ligands, two O,N,O-Schiff bases are bridged by a xanthene backbone. The reactions of H4L1 or H4L2 with manganese salts afforded tetra- and dinuclear manganese complexes, including the tetramanganese(ii,ii,iii,iii) complex [Mn4(L1)2(μ-OAc)2] with a Mn4O6 core exhibiting an incomplete double-cubane structure. In the Mn4O6 core, phenolate and alkoxide O atoms bridge the manganese ions. Deprotonated 3-hydroxypropyl groups were crucial to the assembly of four manganese ions because the phenolate-bridged dimanganese(iii,iii) complex [Mn2(H2L1)2]2+ was obtained in the absence of a base, and H4L2, which has 2-hydroxybenzyl groups instead of 3-hydroxypropyl groups in H4L1, afforded the cyclic dimanganese(iv,iv) complex [Mn2(L2)2]. We disclosed that [Mn4(L1)2(μ-OAc)2] was converted to the oxo-bridged tetramanganese(iii,iii,iii,iii) complex [Mn4(L1)(HL1)(μ3-O)(μ-OAc)2]+ by treating with NH4PF6 or NH4BF4: a triply bridging alkoxide was protonated and replaced by an oxide ligand. The cyclic voltammograms of [Mn4(L1)(HL1)(μ3-O)(μ-OAc)2]+ suggested that the reverse reaction forming [Mn4(L1)2(μ-OAc)2] occurred in the electrochemical processes and was assisted by protonation.

Synthesis, Structure, and Catalytic Epoxidation Property of a New Phenolato and μ1,1,3-Azido Co-Bridged Polynuclear Manganese(III) Complex Derived from N,N′-Bis(5-methylsalicylidene)ethane-1,2-diamine

A new phenolato and μ1,1,3-azido co-bridged polynuclear manganese(iii) complex has been synthesised and characterised. The structure of the complex has been confirmed by single crystal X-ray diffraction analyses. The ability of the complex to catalyse the epoxidation of styrene using PhIO or NaOCl as oxidant has been studied. Results show the catalysis to occur efficiently in the presence of PhIO and NaOCl.

Discrete polynuclear manganese(ii) complexes with thiacalixarene ligands: synthesis, structures and photophysical properties.

The synthesis, crystal structure and photophysical properties of the new compound [Mn4(ThiaSO2)2F][K(18-crown-6)], ThiaSO2 = p-tert-butylsulphonylcalix[4]arene, are presented and compared to the ones of [Mn4(ThiaSO2)2F]K. The strong orange luminescence is attributed to the Mn(2+) centred (4)T1→(6)A1 transition. Its temperature and pressure dependence and quenching by molecular dioxygen are reported. The latter is attributed to energy transfer from the (4)T1 state exciting dioxygen to its (1)∑(+)g state. In the solid state, the quenching is much more efficient in [Mn4(ThiaSO2)2F][K(18-crown-6)] than in [Mn4(ThiaSO2)2F]K. This is attributed to the open pore structure of the former allowing fast diffusion of dioxygen into the crystal lattice.

Formation of octapod MnO nanoparticles with enhanced magnetic properties through kinetically-controlled thermal decomposition of polynuclear manganese complexes

Polynuclear manganese complexes are used as precursors for the synthesis of manganese oxide nanoparticles (MnO NPs). Altering the thermal decomposition conditions can shift the nanoparticle product from spherical, thermodynamically-driven NPs to unusual, kinetically-controlled octapod structures. The resulting increased surface area profoundly alters the NP's surface-dependent magnetism and may have applications in nanomedicine.

A Spin-Canted Polynuclear Manganese Complex Comprised of Alternating Linkage of Cyclic Tetra-and Mononuclear Fragments

A polynuclear manganese complex composed of alternating cyclic tetramer and monomer has been solvothermally prepared and magnetically characterized. Magnetic analyses indicate that the title compound shows spin-canting behavior.

Coordination Polymers Containing Manganese(II)-Azido Layers Connected by Dipyridyl-tetrazine and 4,4′-Azobis(pyridine) Linkers

Two new polynuclear manganese(II) complexes [Mn(dptz)(N(3))(2)](n) (1) and [Mn(azpy)(N(3))(2)](n) (2) (where dptz = dipyridyl-tetrazine and azpy = 4,4'-azobis(pyridine)) have been synthesized by self-assembly of the ligand azide, together with dptz and azpy as secondary spacers. The compounds are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. The structural analyses reveal that in complex 1, which is the first reported Mn(II) complex with the ligand dptz, two μ(1,3) bridging azides connect neighboring manganese ions in a zigzag manner to generate a neutral two-dimensional (2D) sheet which is further connected by the dptz ligands to form a three-dimensional (3D) framework. By contrast, complex 2 contains dimeric [Mn(2)(μ(1,1)-N(3))(2)](2+) fragments linked to four identical motifs by means of four single μ(1,3)-N(3) bridges, that generates a neutral 2D Mn(II)-azide sheet which is further interconnected by azpy ligands to neighboring manganese ions forming an unprecedented 3D network. Variable-temperature (2-300 K) magnetic susceptibility measurements show the presence of predominantly antiferromagnetic coupling for both complexes that has been reproduced with a regular antiferromagnetic S = 5/2 chain (J) with interchain interactions (j) modeled with the molecular field approximation with J = -7.1 cm(-1) and j' = -0.8 cm(-1) for 1 and J = -4.2 cm(-1) and j' = 0.1 cm(-1) for 2.

A facile “bottom-up” approach to prepare free-standing nano-films based on manganese coordination clusters

We present herein a novel method to prepare free-standing Dried Foam Films (DFFs) whereby individual polynuclear manganese complexes cover quantitatively the holes of micro-grids; the fabricated, homogeneous films have a cross-sectional thickness of only ca. 5 nm and are characterised by high mechanical stability.

Two different coordination geometries in polynuclear manganese(II) complexes with bis(μ-phosphinato) bridges

Four new polynuclear phosphinato-bridged manganese(II) complexes, three dinuclear compounds [Mn(μ-dpp)(5-dmbpy)(NO3)]2 (1), [Mn(μ-dpp)(Me-phen)(NO3)]2 (2), [Mn(μ-bmp)(neocuproine)(NO3)]2 (3) and a 1D compound [Mn(μ-bmp)2]n (4) where Hdpp is diphenylphosphinic acid, Hbmp is bis(4-methoxyphenyl)phosphinic acid, 5-dmbpy=5,5′-dimethyl-2,2′-dipyridyl, Me-phen=methyl-1,10-phenanthroline and neocuproine=2,9-dimethyl-1,10-phenanthroline, have been synthesized and structurally characterized by X-ray crystallography. In this series, the dinuclear structures consist in a bis(diphenylphosphinato) (dpp) or a bis(4-methoxyphenyl)phosphinato (bmp) anion bridging the two Mn(II) centers in a syn–syn coordination mode for 1–3. The monodimensional compound 4 is built from double bridging syn–syn bis(4-methoxyphenyl)phosphinato anions. The coordination geometry around the Mn(II) ions in 1–3 is six-coordinate with distorted octahedral environment. Moreover, the coordination geometry around the Mn(II) ions in 4 is tetrahedral. The magnetic behavior of these complexes is reported. The complexes show weak antiferromagnetic coupling with J in the range 0.05–0.43cm−1 for 1–3 and 0.88cm−1 for 4. The magnetic properties are discussed in relation to the structural data.

Syntheses, structures and magnetic properties of μ 1,5-dicyanamide bridged di- and polynuclear manganese(II) complexes containing neutral N-donor Schiff bases: Control of coordination number and nuclearity by varying denticity

Two hexacoordinated dinuclear compounds [Mn(L1)(dca)] 2(ClO 4/PF 6) 2·CH 3OH ( 1/2) and two heptacoordinated coordination polymers [Mn(L2)(dca)] n (ClO 4/PF 6) n ( 3/ 4) [L1 = N, N′-(bis-(pyridin-2-yl)benzylidene)-1,3-propanediamine; L2 = N, N′-(bis-(pyridin-2-yl)benzylidene)diethylenetriamine; dca = dicyanamide] are synthesized and characterized. Structures of 1– 3 have been solved by X-ray diffraction measurements. Each manganese(II) center in 1/ 2 is located in a distorted octahedral environment with an MnN 6 chromophore coordinated by the four N atoms of L1 and two nitrile N atoms of bibridged μ 1,5 dca. Interestingly, the coordination polymer 3 forms a 1D chain through single Mn–(NCNCN)–Mn units in which each manganese(II) center adopts a pentagonal bipyramidal geometry with an MnN 7 chromophore occupied with five N atoms of L2 and two nitrile N atoms of monobridged μ 1,5 dca. Magnetic susceptibility measurements of 1– 3 in the 2–300 K temperature range reveal weak antiferromagnetic interactions.

Polynuclear manganese amino acid complexes

The reaction of MnCl(2).4H(2)O with DL-valine (Val) in MeOH in the presence of Et-saoH(2) (2-hydroxypropiophenone oxime) and NEt(4)OH forms the complex [Mn(III)(3)Mn(IV)(2)O(2)(CH(3)O)(Et-sao)(6)(Val)].Val.1.5H(2)O (1.Val.1.5H(2)O) in very good yields. A similar reaction of MnCl(2).4H(2)O with Glycine (Gly) in MeOH in the presence of saoH(2) (salicylaldoxime) and Ca(OH)(2) yields the complex [Mn(III)(3)O(sao)(3)(Gly)Cl(MeOH)(3)].1.87 MeOH.0.13H(2)O (2.1.87 MeOH.0.13H(2)O). Replacing saoH(2) with Me-saoH(2) (2-hydroxyethanone oxime) and Gly with HPABA (para-aminobenzoic acid) in the presence of CH(3)ONa in MeOH forms the complex [Mn(6)O(2)(PABA)(2)(Me-sao)(6)(MeOH)(4)(H(2)O)(2)].2[Mn(6)O(2)(PABA)(2)(Me-sao)(6)(MeOH)(2)].11 MeOH (3.11 MeOH) in moderate yields. Magnetic studies for 1 and 2 reveal the presence of both ferromagnetic and antiferromagnetic interactions, leading to S = 2 ground states for both complexes. Complexes 1 and 2 represent the first examples of polynuclear manganese complexes with any naturally occurring alpha-amino acid, while 3 is the first structurally characterised example of a manganese para-aminobenzoate complex.

Can theoretical methods go beyond the experimental data? The case of molecular magnetism

The complexity of polynuclear transition metal complexes with the most appealing magnetic properties makes it impossible to extract the values of exchange interactions between the paramagnetic centers using experimental techniques. Hence, theoretical methods based on density functional theory are used because they allow the accurate estimation of such values. Three Mn(6) complexes were studied and the calculated exchange coupling constants used to plot a magnetic susceptibility curve that can be compared with the experimental ones. We propose a new tool to facilitate the understanding of the magnetic properties in systems of this kind. We employed magnetostructural maps to correlate the calculated exchange coupling constants with structural parameters for the dinuclear or polynuclear manganese complexes that we have studied.

Synthesis, structures and magnetic properties of polynuclear mixed-valence MnIIMnIII complexes containing 3-(2-phenol)-5-(pyridin-2-yl)-1,2,4-triazole ligand

This paper reports the synthesis, crystal structures, and magnetic properties of a series of mixed-valence polynuclear manganese complexes bridged by a dianionic 1,2,4-triazole-based ligand L(2-) (H(2)L = 3-(2-phenol)-5-(pyridin-2-yl)-1,2,4-triazole). Complexes 1 to 3 show a similar binuclear structure, with the central core of [Mn(II)Mn(III)(L)(2)] and some other small molecules also coordinated to the two Mn centers. The two [Mn(II)Mn(III)(L)(2)] subunits can be further connected by different dicarboxylic acids to construct non-charged tetranuclear complexes 4 to 7. In these complexes, each deprotonated dianionic ligand L(2-) acts as a mu(2)-bridged ligand to coordinate two Mn centers via the 1,2,4-triazole ring. Bond valence sum (BVS) calculations and Mn surrounding bond lengths indicate that the Mn center coordinated to the pyridine N atoms in the +2 oxidation state, while another Mn center coordinated to the phenolic O atoms is in the +3 oxidation state. The Mn(III) centre shows Jahn-Teller elongation along one of the axes. Magnetic studies show the presence of ferromagnetic Mn(III)-Mn(II) coupling in the binuclear (1-3) and tetranuclear (4-7) complexes with the magnetic coupling constant (J) ranging from 0.58 to 1.17 cm(-1), based on the Hamiltonian H = -2JS(1) x S(2) (S(1) = 5/2 and S(2) = 2). In all cases both z'J' (intermolecular interactions) and D parameter (Zero Field Splitting of the Mn (III) ion) has been introduced to improve the corresponding fit. The relationship of the coupling interaction between the Mn(II)/Mn(III) and their electronic structures is discussed.

Desulfuration and Cyclization of (Z)‐2‐[Amino(pyridine‐2‐yl)methylene]‐ hydrazonecarbothioamide in the Presence of Manganese(II)

AbstractThe reaction of (Z)‐2‐[amino(pyridine‐2‐yl)methylene]hydrazonecarbothioamide (HAm4DH) with Mn(ClO4)2·6H2O afforded different mononuclear or polynuclear manganese(II) complexes, the nature of which apparently depended on the solvent used. For example, in ethanol a compound of formula [Mn(HAm4DH)2](ClO4)2 (1) was obtained, where HAm4DH coordinates as a common tridentate NNS donor, but the [Mn(bpy)2(NCS)2] complex (2) (bpy = 2,2'‐bipyridine) has also been obtained – probably due to C–N bond cleavage of the thiosemicarbazone. Nevertheless, in a basic aqueous medium [Mn(bpy)3](ClO4)2·0.5bpy (3) is formed and there is structural evidence for chemical transformations of the thiosemicarbazone promoted by MnII. Thus, the sulfate in {[Mn(py)4Mn(py)2(H2O)2(μ‐SO4)2]·4H2O}n (4) or sulfate and cyclooctasulfur in [Mn(pta)2(pdo)]4(SO4)2·4H2O·S8] (5), where pta is 3‐(pyridin‐2‐yl)‐1,2,4‐triazol‐5‐amine and pdo is (2R,4R/2S,4S)‐pentane‐2,4‐diolato, arise from the desulfuration and oxidation of the thiosemicarbazone ligand. The structures of complexes 2 to 5 were established by single‐crystal X‐ray diffraction. The formation of pta is the result of the oxidative cyclization of HAm4DH. In the polynuclear complex 4, the sulfate acts as an (O,O') bridge between alternating Mn(py)2(H2O)2 and Mn(py)4 centers. In the tetranuclear complex 5, pta acts as a bischelating ligand through the N‐pyridine and N‐triazole, and pdo act as a bridge between two manganese atoms. It is also noteworthy that in complexes 4 and 5 hydrogen bonds give rise to different self‐assembly behaviour that leads to complicated supramolecular structures.

PH-Directed assembly and magnetic properties of two polynuclear Mn II complexes: (Δ, Λ)-{Mn 3(phen) 2(OOCCH 3) 6} and 1-D [Mn(phen)Cl 2] n

When the reaction conditions are deliberately controlled by the pH, two different polynuclear manganese complexes, (Δ, Λ)-{Mn 3(phen) 2 (CH 3COO) 6} ( 1) and [Mn(phen)Cl 2] n ( 2) (phen = 1,10-phenanthroline), have been synthesized from the same raw materials. The structural analyses show that 1 has a structure formed by neutral chiral linear trinuclear molecules, while 2 has a structure consisting of one-dimensional infinite chains. A study of the temperature dependent magnetic susceptibilities reveal that 1 is an antiferromagnetically coupled trimer molecule while 2 shows ferromagnetic interactions within the chain.

Synthesis, Crystal Structure, and Cytochrome P450-Like Hydroxylation Property of a Novel Azido-Bridged Manganese(III) Complex Derived from 2-[(2-Phenylaminoethylimino)Methyl]Phenol

A novel end-to-end azido-bridged polynuclear manganese(III) complex, [MnL 2 ( μ 1,3 -N 3 )] · 2MeCN (HL = 2-[(2-phenylaminoethylimino)methyl]phenol), has been synthesized and characterized by elemental analysis, IR, and single crystal X-ray diffraction. Each Mn III atom in the complex has an octahedral coordination, being coordinated by two phenolic O and two imine N atoms from two Schiff base ligands, and by two terminal N atoms from two bridging azide groups. The determination studied by GC/MS analysis indicated that the complex has catalytic property for the dioxygen oxidization of cyclohexane.

Families of Polynuclear Manganese, Cobalt, Nickel and Copper Complexes Stabilized by Various Forms of Di‐2‐pyridyl Ketone

AbstractFor Abstract see ChemInform Abstract in Full Text.

Families of Polynuclear Manganese, Cobalt, Nickel and Copper Complexes Stabilized by Various Forms of Di-2-pyridyl Ketone

The synthetic and structural chemistry of polynuclear manganese, cobalt, nickel and copper carboxylate complexes, stabilized by various forms of di-2-pyridyl ketone, is discussed. The structural diversity displayed by the described complexes stems from the ability of the doubly and singly deprotonated forms of the gem-diol form of di-2-pyridyl ketone, or the monoanion of the hemiacetal form of this ligand, to adopt a variety of coordination modes. The nuclearities of the clusters vary from four to fourteen. Perhaps the most aesthetically pleasing families are the "flywheel Cu 12 clusters, and the Co 9 and Ni 9 complexes in which the nine metal ions adopt a topology of two square pyramids sharing a common apex. A means of increasing the ground-state total spin value of a polynuclear 3d-metal cluster is also proposed. The approach is based on the replacement of hydroxo bridges, that most often propagate antiferromagnetic exchange interactions in clusters, by the end-on azido ligand, which is a well known ferromagnetic coupler. This approach involves "true" reactivity chemistry on pre-isolated clusters and the products are not undergone significant structural changes, except for the azido-for-hydroxo substitution, compared to the starting materials/clusters.