Mechanistic disparity in the electron transfer reactions of thiosulfate with di‐μ‐oxo‐bis(1,4,8,11‐tetraazacyclotetradecane)‐dimanganese(III,IV) and di‐μ‐oxo‐bis(1,4,7,10‐tetraazacyclododecane)‐dimanganese(III,IV) complexes

A comparative kinetic study of the reactions of two mixed valence manganese(III,IV) complexes of macrocyclic ligands, [L¹Mn^IV(O)₂Mn^IIIL¹], 1 (L¹ = 1,4,8,11‐tetraazacyclotetradecane) and [L²Mn^IV(O)₂Mn^IIIL²], 2 (L² = 1,4,7,10‐tetraazacyclododecane) with thiosulfate has been carried out by spectrophotometry in aqueous buffer at 30°C. Reaction between complex 1 and thiosulfate follows a first‐order rate saturation kinetics. The pH dependency and kinetic evidences suggest the participation of two complex species of Mn^III(μ‐O)₂Mn^IV under the experimental conditions. Detailed kinetic study shows that reduction of 2 proceeds through an autocatalytic path where the intermediate (Mn^III)₂ species has been assumed to catalyze the reaction. The difference in the reaction mechanisms is ascribed to the difference in stability of the intermediate complex species, the evidence for which comes from the electrochemical behavior of the complexes and time dependent EPR spectroscopic measurements during the reduction of 2 . © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 119–128, 2004     

Kinetics and mechanism of oxidation of 2‐mercaptosuccinic acid by bis(μ‐oxo)‐ manganese(III,IV)‐cyclam complex in aqueous medium: Influence of externally added copper(II)

Kinetic studies on the oxidation of 2‐mercaptosuccinic acid by dinuclear [Mn₂^III/IV(μ‐O)₂(cyclam)₂](ClO₄)₃] ( 1 ) (abbreviated as Mn^III–Mn^IV) (cyclam = 1,4,8,11‐tetraaza‐cyclotetradecane) have been carried out in aqueous medium in the pH range of 4.0–6.0, in the presence of acetate buffer at 30°C by UV–vis spectrophotometry. In the pH region, two species of complex 1 (Mn^III–Mn^IV and Mn^III–Mn^IVH, the later being μ‐O protonated form) were found to be kinetically significant. The first‐order dependence of the rate of the reactions on [Thiol] both in presence and absence of externally added copper(II) ions, first‐order dependence on [Cu²⁺] and a decrease of rate of the reactions with increase in pH have been rationalized by suitable sequence of reactions. Protonation of μ‐O bridge of 1 is evidenced by the perchloric acid catalyzed decomposition of 1 to mononuclear Mn(III) and Mn(IV) complex observed by UV–vis and EPR spectroscopy. The kinetic features have been rationalized considering Cu(RSH) as the reactive intermediate. EPR spectroscopy lends support for this. The formation of a hydrogen bonded outer‐sphere adduct between the reductant and the complex in the lower pH range prior to electron transfer reactions is most likely to occur. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 170–177 2004     

Bis[μ3‐1,8‐bis(triisopropylsilylamido)naphthalene]bis(tetrahydrofuran)di‐μ3‐oxido‐dimanganese(III)disodium

The solid‐state structure of the title compound, [Na₂Mn₂(C₃₂H₅₆N₂OSi₂)₂O₂] or [1,8‐C₁₀H₆(NSiⁱPr₃)₂Mn(μ₃‐O)Na(THF)]₂, which lies across a crystallographic twofold axis, exhibits a central [Mn₂O₂Na₂]⁴⁺ core, with two oxide groups, each triply bridging between the two Mn^III ions and an Na⁺ ion. Additional coordination is provided to each Mn^III centre by a 1,8‐C₁₀H₆(NSiⁱPr₃)₂ [1,8‐bis(triisopropylsilylamido)naphthalene] ligand and to the Na⁺ centres by a tetrahydrofuran molecule. The presence of an additional Na...H—C agostic interaction potentially contributes to the distortion around the bridging oxide group.     

A mixed‐valence manganese(III)–manganese(IV) di‐μ‐oxo complex, [(cyclam)MnO]2(ClO4)2(NO3)

The title dinuclear di‐μ‐oxo‐bis­[(1,4,8,11‐tetra­aza­cyclo­tetra­decane‐κ⁴N)­manganese(III,IV)] diperchlorate nitrate complex, [Mn₂O₂(C₁₀H₂₄N₄)₂](ClO₄)₂(NO₃) or [(cyclam)Mn­O]₂(ClO₄)₂(NO₃), was self‐assembled by the reaction of Mn²⁺ with 1,4,8,11‐tetra­aza­cyclo­tetra­decane in aqueous media. The structure of this compound consists of a centrosymmetric binuclear [(cyclam)MnO]³⁺ unit, two perchlorate anions and one nitrate anion. While the low‐temperature electron paramagnetic resonance spectra show a typical 16‐line signal for a di‐μ‐oxo Mn^III/Mn^IV dimer, the magnetic susceptibility studies also confirm a characteristic antiferromagnetic coupling between the electronic spins of the Mn^IV and Mn^III ions.     

A novel heterometallic dinuclear compound: rac‐pentaaqua‐1κ5O‐(μ‐2‐sulfidoacetato‐1:2κ3O:O′,S)bis(2‐sulfidoacetato‐2κ2O,S)manganese(II)tin(IV)

The title racemic heterometallic dinuclear compound, [MnSn(C₂H₂O₂S)₃(H₂O)₅], (I), contains one main group Sn^IV metal centre and one transition metal Mn^II centre, and, by design, links the Mn^II centre to the building unit of the (Δ/Λ) [SnL₃]²⁻ complex anion (L is the 2‐sulfidoacetate dianion). In this cluster, the Sn^IV centre of the (Δ/Λ) [SnL₃]²⁻ unit is coordinated by three O atoms and three S atoms from three L ligands to form an [SnO₃S₃] octahedral coordination environment. The Mn^II centre is in an [MnO₆] octahedral coordination environment, with five O atoms from five water molecules and the sixth from the μ₂‐L ligand of the (Δ/Λ) [SnL₃]²⁻ unit. Between adjacent dinuclear molecules, there are many hydrogen‐bond interactions of O—H...O, O—H...S, C—H...O and C—H...S types. Of these, eight pairs of O—H...O hydrogen bonds fuse all the dinuclear molecules into two‐dimensional supramolecular sheets along the bc plane. Adjacent supramolecular sheets are further connected through O—H...S hydrogen bonds to give a three‐dimensional supramolecular network.     

Bis(μ‐6‐hydroxy­picolinato)‐μ‐oxo‐bis­[di­pyridine­manganese(III)] monohydrate

The title compound, [Mn₂(μ‐O)(C₆H₃NO₃)₂(C₅H₅N)₄]·H₂O, was isolated from the reaction of 2,6‐pyridine­di­carboxylic acid with [Mn₁₂O₁₂(CH₃COO)₁₆(H₂O)₄] in pyridine. The dimanganese complex has twofold symmetry; the Mn^III atoms are bridged by one oxo and two amidate ligands and show compressed octahedral Jahn–Teller distortion. The molecular packing comprises a three‐dimensional structure constructed by means of extensive intermolecular interactions, including three kinds of hydrogen bonds and π–π interactions.     

catena‐Poly[[bis(μ‐2‐sulfonatobenzoato)bis[triaquagadolinium(III)]]‐μ‐oxalato]

The asymmetric unit of the title coordination polymer, [Gd₂(C₇H₄O₅S)₂(C₂O₄)(H₂O)₆]_n or [Gd(2‐SB)(ox)_0.5(H₂O)₃]_2n (2‐SB is 2‐sulfonatobenzoate and ox is oxalate), (I), consists of one Gd^III ion, one 2‐SB anion, three coordinated water molecules and one half of an ox ligand. The ox ligand is located on a crystallographic inversion centre. The Gd^III centre shows a distorted tricapped trigonal–prismatic coordination formed by nine O atoms from two 2‐SB anions, one ox ligand and three coordinated water molecules. The carboxylate and sulfonate groups of the 2‐SB anions adopt μ₂‐η¹:η² and μ₁‐η⁰:η⁰:η¹ coordination modes to link two Gd^III ions, generating a centrosymmetric binuclear [Gd₂(2‐SB)₂(H₂O)₆]²⁻ subunit. The ox ligand acts as a bridge, linking the binuclear [Gd₂(2‐SB)₂(H₂O)₆]²⁻ subunits into a one‐dimensional chain structure parallel to the b axis. Furthermore, extensive O—H...O hydrogen bonds connect the chains into a three‐dimensional supramolecular architecture.     

Poly[[bis(pyridin‐3‐ol)manganese(II)]‐di‐μ‐pyridin‐3‐olato]

In the title complex, [Mn(C₅H₄NO)₂(C₅H₅NO)₂]_n or [Mn(μ‐3‐PyO)₂(3‐PyOH)₂]_n (3‐PyO⁻ is the pyridin‐3‐olate anion and 3‐PyOH is pyridin‐3‐ol), the Mn^II atom lies on an inversion centre and has octahedral geometry, defined by two N atoms and two deprotonated exocyclic O atoms of symmetry‐related pyridin‐3‐olate ligands [Mn—N = 2.3559 (14) Å and Mn—O = 2.1703 (11) Å], as well as two N atoms of terminal 3‐PyOH ligands [Mn—N = 2.3482 (13) Å]. The Mn^II atoms are bridged by the deprotonated pyridin‐3‐olate anion into a layer structure, generating sheets in the (01) plane. These sheets are linked by O—H⋯O hydrogen bonds. There are also π–π and C—H⋯π interactions in the crystal structure.     

Di‐μ‐oxido‐bis{bis[N,N′‐bis(2‐pyridylmethyl)ethane‐1,2‐diamine]manganese(III,IV)} tris(perchlorate) hexahydrate: clarification of an order–disorder phase transition

The title compound, [Mn₂O₂(C₁₄H₁₈N₄)₂](ClO₄)₃·6H₂O, contains a mixed‐valent Mn^III/Mn^IV complex. In accordance with a previous report [Collins, Hodgson, Michelsen & Towle (1987). J. Chem. Soc. Chem. Commun. pp. 1659–1660], the structure at 295 K is best described in the space group C2/c, with the complex exhibiting twofold rotational symmetry, and with half site occupancy for one perchlorate anion and several solvent water molecules. At 180 K, the structure is ordered in the subgroup P2₁/n and is clearly shown to be a hexahydrate, rather than the previously reported trihydrate. The origin of the order–disorder phase transition lies in the thermal motion of the perchlorate anions.     

Mechanistic Insight into the Nitric Oxide Dioxygenation Reaction of Nonheme Iron(III)–Superoxo and Manganese(IV)–Peroxo Complexes

Reactions of nonheme Fe^III–superoxo and Mn^IV–peroxo complexes bearing a common tetraamido macrocyclic ligand (TAML), namely [(TAML)Fe^III(O₂)]^2? and [(TAML)Mn^IV(O₂)]^2?, with nitric oxide (NO) afford the Fe^III–NO₃ complex [(TAML)Fe^III(NO₃)]^2? and the Mn^V–oxo complex [(TAML)Mn^V(O)]^? plus NO₂^?, respectively. Mechanistic studies, including density functional theory (DFT) calculations, reveal that M^III–peroxynitrite (M=Fe and Mn) species, generated in the reactions of [(TAML)Fe^III(O₂)]^2? and [(TAML)Mn^IV(O₂)]^2? with NO, are converted into M^IV(O) and ^.NO₂ species through O?O bond homolysis of the peroxynitrite ligand. Then, a rebound of Fe^IV(O) with ^.NO₂ affords [(TAML)Fe^III(NO₃)]^2?, whereas electron transfer from Mn^IV(O) to ^.NO₂ yields [(TAML)Mn^V(O)]^? plus NO₂^?.     

A novel one‐dimensional complex: catena‐poly­[[manganese(III)‐di‐μ‐2‐[(2‐hydroxy­ethyl)­imino­methyl]­phenolato‐κ2O1,N:κO2;κO2:κ2O1] chloride]

In the title one‐dimensional complex, {[Mn^III(C₉H₁₀NO₂)₂]Cl}_n, the Schiff base ligand 2‐[(2‐hydroxy­ethyl)­imino­methyl]­phenolate (Hsae⁻) functions as both a bridging and a chelating ligand. The Mn^III ion is six‐coordinated by two N and four O atoms from four different Hsae⁻ ligands, yielding a distorted MnO₄N₂ octahedral environment. Each [Mn^III(Hsae)₂]⁺ cationic unit has the Mn atom on an inversion centre and each [Mn^III(Hsae)₂]⁺ cation lies about another inversion centre. The chain‐like complex is further extended into a three‐dimensional network structure through Cl⋯H—O hydrogen bonds and C—H⋯π contacts involving the Hsae⁻ rings.     

A pentanuclear bimetallic complex of manganese(II) and aluminium(III) ions: tetra‐μ2‐iodido‐iodidobis(μ3‐2‐methoxyethanolato)bis(μ2‐2‐methoxyethanolato)dimethyl(tetrahydrofuran‐κO)aluminium(III)tetramanganese(II)

The molecule of the title compound, [Mn₄Al(CH₃)₂(C₃H₇O₂)₄I₅(C₄H₈O)], contains one Al^III and four Mn^II ions. Two Mn atoms are five‐coordinate in the form of a trigonal bipyramid or a square pyramid. The two other Mn atoms are six‐coordinate with an octahedral geometry. The fourcoordinate Al atom is linked to the manganese core by μ‐O_alkoxo bridges, forming an almost planar five‐membered ring.     

Coordination Chemistry of Homoleptic Actinide(IV)–Thiocyanate Complexes

The synthesis, X‐ray crystal structure, vibrational and optical spectroscopy for the eight‐coordinate thiocyanate compounds, [Et₄N]₄[Pu^IV(NCS)₈], [Et₄N]₄[Th^IV(NCS)₈], and [Et₄N]₄[Ce^III(NCS)₇(H₂O)] are reported. Thiocyanate was found to rapidly reduce plutonium to Pu^III in acidic solutions (pH<1) in the presence of NCS^?. The optical spectrum of [Et₄N][SCN] containing Pu^III solution was indistinguishable from that of aquated Pu^III suggesting that inner‐sphere complexation with [Et₄N][SCN] does not occur in water. However, upon concentration, the homoleptic thiocyanate complex [Et₄N]₄[Pu^IV(NCS)₈] was crystallized when a large excess of [Et₄N][NCS] was present. This compound, along with its U^IV analogue, maintains inner‐sphere thiocyanate coordination in acetonitrile based on the observation of intense ligand‐to‐metal charge‐transfer bands. Spectroscopic and crystallographic data do not support the interaction of the metal orbitals with the ligand π system, but support an enhanced An^IV–NCS interaction, as the Lewis acidity of the metal ion increases from Th to Pu.     

Aquachloro[N,N′‐ethylenebis(salicylideneiminato)]manganese(III)

The title compound, aqua­chloro{2,2′‐[1,2‐ethanediyl­bis­(nitrilo­methyl­idyne)]­diphenolato‐κ⁴O,N,N′,O′}manganese(III),[MnCl(C₁₆H₁₄N₂O₂)(H₂O)], is a neutral manganese(III) complex with a pseudo‐octahedral metal centre. The equatorial plane comprises the four donor atoms of the tetradentate Schiff base ligand [Mn—O 1.886 (4) and 1.893 (4) Å, and Mn—N 1.978 (5) and 1.982 (5) Å], with a water mol­ecule [Mn—O 2.383 (4) Å] and a Cl^? ligand [Mn—Cl 2.4680 (16) Å] completing the coordination sphere. The distorted geometry is highlighted by the marked displacement of the Mn^III ion out of the least‐squares plane of the four Schiff base donor atoms by 0.165 (2) Å. These monomeric Mn^III centres are then linked into a polymeric array via hydrogen bonds between the coordinated water mol­ecule and the phenolic O‐atom donors of an adjacent Mn^III centre [O—H?O 2.789 (5) and 2.881 (5) Å].     

Kinetics of oxidation of hydrazine by a dioxo-bridged dimanganese(III,IV) complex ion

In aqueous acidic media containing an excess of Hbipy⁺–bipy buffer in the pH 3.5–4.5 range, the complex ion [(bipy)₂Mn^III(-O)₂Mn^IV(bipy)₂]³⁺ (1) coexists in rapid equilibrium with its diaqua derivative [Mn^III,IV ₂ (-O)₂(bipy)₃(H₂O)₂]³⁺ (1a) (bipy = 2,2-bipyridine). An excess of N₂H₅ ⁺ quantitatively reduces the mixture to Mn^II, itself being oxidised to N₂. The first order rate constant, k _o decreases with increasing C _bipy (C _bipy = [Hbipy⁺] + [bipy]) but increases with increasing [N₂H₅ ⁺] and [H⁺]. The observed kinetic dependence can be explained in terms of a reaction between (1a) and N₂H₅ ⁺. Replacement of solvent H₂O with D₂O decreases k _o substantially and the effect suggests simultaneous transfer of an electron and a proton in the rate-determining step. The relevance of this observation to the delayed oxidation of H₂O in the hydrazine-treated photosystem II is discussed.     

catena‐Poly[[diaquamanganese(II)]‐di‐μ‐1,1,3,3‐tetracyano‐2‐ethoxypropenido‐κ4N1:N3]

The crystal structure of the title compound, [Mn(C₉H₅N₄O)₂(H₂O)₂], conventionally denoted Mn(EtO‐TCA)₂(H₂O)₂, where EtO‐TCA is 2‐ethoxy‐1,1,3,3‐tetra­cyano­propenide, is described. The EtO‐TCA anions bridge Mn^II centers through one of the nitrile N atoms of each of their two di­cyano­methanide groups, thus forming dibridged chains along ab. These chains are linked into two‐dimensional sheets through hydrogen bonding. The seven‐atom bridge, which results in a long Mn⃛Mn intrachain interaction [9.0044 (4) Å], as well as the large interchain separations [8.3288 (4) and 8.5220 (4) Å] prohibit long‐range magnetic ordering down to temperatures as low as 1.55 K.     

Bis(2‐amino‐1H‐benzimidazol‐3‐ium) tetrakis(μ‐but‐2‐enoato)‐κ4O:O′;κ3O,O′:O;κ3O:O,O′‐bis[bis(but‐2‐enoato‐κ2O,O′)holmium(III)]

The title ionic compound, (C₇H₈N₃)₂[Ho₂(C₄H₅O₂)₈], is constructed from two almost identical independent centrosymmetric anionic dimers balanced by two independent 2‐amino‐1H‐benzimidazol‐3‐ium (Habim⁺) cations. The asymmetric part of each dimer is made up of one Ho^III cation and four crotonate (crot or but‐2‐enoate) anions, two of them acting in a simple η²‐chelating mode and the remaining two acting in two different μ₂:η² fashions, viz. purely bridging and bridging–chelating. Symmetry‐related Ho^III cations are linked by two Ho—O—Ho and two Ho—O—C—O—Ho bridges which lead to rather short intracationic Ho...Ho distances [3.8418 (3) and 3.8246 (3) Å]. In addition to the obvious Coulombic interactions linking the cations and anions, the isolated [Ho₂(crot)₈]²⁻ and Habim⁺ ions are linked by a number of N—H...O hydrogen bonds, in which all N—H groups of the cation are involved as donors and all (simple chelating) crot O atoms are involved as acceptors. These interactions result in compact two‐dimensional structures parallel to (110), which are linked to each other by weaker π–π contacts between Habim⁺ benzene groups.     

Di‐μ‐chlorido‐bis[dichloridobis(methylamido‐κN)bis(methylamine‐κN)titanium(IV)]

The title compound, [Ti₂Cl₆(C₂H₆N)₂(C₂H₇N)₂], is a binuclear octahedral complex lying about an inversion centre. There are four different chloride environments, two terminal [Ti—Cl = 2.2847 (5) and 2.3371 (5) Å] and two bridging [Ti—Cl = 2.4414 (5) and 2.6759 (5) Å], with the Ti—Cl distances being strongly influenced by both the ligand trans to the chloride and whether or not the chloride anion is bridging between the two Ti^IV centres. The compound forms a two‐dimensional network in the solid state, with weak intermolecular C—H...Cl interactions giving rise to a planar network in the (10) plane.     

catena‐Poly[[[diaqua­[trans‐3‐(4‐pyri­dyl)acrylato]samarium(III)]‐di‐μ‐trans‐3‐(4‐pyrid­yl)acrylato] dihydrate]

In the title compound, {[Sm(4‐pya)₃(H₂O)₂]·2H₂O}_n [4‐pya is trans‐3‐(4‐pyrid­yl)acrylate, C₈H₆NO₂], each Sm^III atom is ten‐coordinated and has a bicapped square‐antiprismatic coordination geometry. There is a crystallographic center of symmetry at the mid‐point of the Sm⋯Sm line within each [Sm(4‐pya)₃(H₂O)₂]₂ dimer. Each dimer is inter­connected by two pairs of bridging 4‐pya ligands to form a one‐dimensional chain. Neighboring chains are connected via hydrogen bonds to form a three‐dimensional network.     

Binuclear Homoleptic Manganese(III,III) and Manganese(IV,III) Complexes with Deprotonated D-Mannose from Aqueous Solution

Just a “reducing” sugar —namely, D -mannose—is a starting material in the synthesis of a mixed-valence complex of manganese in the oxidation states +III and +IV . Ba₂[Mn^IIIMn^IV(β-D -ManfH₋₅)₂]Cl⋅14 H₂O (Manf=mannofuranose; the structure of the anion is shown on the right) is prepared in aqueous solution by oxidation of an analogous Mn₂^III complex with oxygen. In neutral solutions the Mn^IIIMn^IV binuclear complex is formed by disproportionation of the Mn₂^III precursor.