Efficient Olefin Epoxidation by Robust Re4 Cluster‐Supported MnIII Complexes with Peracids: Evidence of Simultaneous Operation of Multiple Active Oxidant Species,MnVO,MnIVO,and MnIII?OOC(O)R

Two new tetranuclear chalcocyanide cluster complexes, [{Mn(saloph)H₂O}₄Re₄Q₄(CN)₁₂]?4 CH₃OH? 8 H₂O (saloph=N,N′‐o‐phenylenebis(salicylidenaminato), Q=Se ( 1 ‐Se), Te ( 2 ‐Te)), have been synthesized by the diffusion of a methanolic solution of [PPh₄]₄[Re₄Q₄(CN)₁₂] into a methanolic solution of [Mn(saloph)]⁺. The structure of 2 ‐Te has been determined by X‐ray crystallography. These rhenium cluster‐supported [Mn^III(saloph)] complexes have been found to efficiently catalyze a wide range of olefin epoxidations under mild experimental conditions in the presence of meta‐chloroperbenzoic acid (mCPBA). Olefin epoxidation by these catalysts is proposed to involve the multiple active oxidants Mn^V?O, Mn^IV?O, and Mn^III? OOC(O)R. Evidence in support of this interpretation has been derived from reactivity and Hammett studies, H₂¹⁸O‐exchange experiments, and the use of peroxyphenylacetic acid as a mechanistic probe. Moreover, it has been observed that the participation of Mn^V?O, Mn^IV?O, and Mn^III? OOC(O)R can be controlled by changing the substrate concentration. This mechanism provides the greatest congruity with related oxidation reactions that employ certain Mn complexes as catalysts.     

Amide‐Based Nonheme Cobalt(III) Olefin Epoxidation Catalyst: Partition of Multiple Active Oxidants CoVO,CoIVO,and CoIII?OO(O)CR

A mononuclear nonheme cobalt(III) complex of a tetradentate ligand containing two deprotonated amide moieties, [Co(bpc)Cl₂][Et₄N] ( 1 ; H₂bpc=4,5‐dichloro‐1,2‐bis(2‐pyridine‐2‐carboxamido)benzene), was prepared and then characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy, and X‐ray crystallography. This nonheme Co^III complex catalyzes olefin epoxidation upon treatment with meta‐chloroperbenzoic acid. It is proposed that complex 1 shows partitioning between the heterolytic and homolytic cleavage of an O? O bond to afford Co^V?O ( 3 ) and Co^IV?O ( 4 ) intermediates, proposed to be responsible for the stereospecific olefin epoxidation and radical‐type oxidations, respectively. Moreover, under extreme conditions, in which the concentration of an active substrate is very high, the Co? OOC(O)R ( 2 ) species is a possible reactive species for epoxidation. Furthermore, partitioning between heterolysis and homolysis of the O? O bond of the intermediate 2 might be very sensitive to the nature of the solvent, and the O? O bond of the Co? OOC(O)R species might proceed predominantly by heterolytic cleavage, even in the presence of small amounts of protic solvent, to produce a discrete Co^V?O intermediate as the dominant reactive species. Evidence for these multiple active oxidants was derived from product analysis, the use of peroxyphenylacetic acid as the peracid, and EPR measurements. The results suggest that a less accessible Co^V?O moiety can form in a system in which the supporting chelate ligand comprises a mixture of neutral and anionic nitrogen donors.     

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^?.     

Dramatic Influence of an Anionic Donor on the Oxygen‐Atom Transfer Reactivity of a MnV–Oxo Complex

Addition of an anionic donor to an Mn^V(O) porphyrinoid complex causes a dramatic increase in 2‐electron oxygen‐atom‐transfer (OAT) chemistry. The 6‐coordinate [Mn^V(O)(TBP₈Cz)(CN)]^? was generated from addition of Bu₄N⁺CN^? to the 5‐coordinate Mn^V(O) precursor. The cyanide‐ligated complex was characterized for the first time by Mn K‐edge X‐ray absorption spectroscopy (XAS) and gives Mn?O=1.53 Å, Mn?CN=2.21 Å. In combination with computational studies these distances were shown to correlate with a singlet ground state. Reaction of the CN^? complex with thioethers results in OAT to give the corresponding sulfoxide and a 2e^?‐reduced Mn^III(CN)^? complex. Kinetic measurements reveal a dramatic rate enhancement for OAT of approximately 24 000‐fold versus the same reaction for the parent 5‐coordinate complex. An Eyring analysis gives ΔH^≠=14 kcal mol^?1, ΔS^≠=?10 cal mol^?1 K^?1. Computational studies fully support the structures, spin states, and relative reactivity of the 5‐ and 6‐coordinate Mn^V(O) complexes.     

Remarkable Solvent,Porphyrin Ligand,and Substrate Effects on Participation of Multiple Active Oxidants in Manganese(III) Porphyrin Catalyzed Oxidation Reactions

The participation of multiple active oxidants generated from the reactions of two manganese(III) porphyrin complexes containing electron‐withdrawing and ‐donating substituents with peroxyphenylacetic acid (PPAA) as a mechanistic probe was studied by carrying out catalytic oxidations of cyclohexene, 1‐octene, and ethylbenzene in various solvent systems, namely, toluene, CH₂Cl₂, CH₃CN, and H₂O/CH₃CN (1:4). With an increase in the concentration of the easy‐to‐oxidize substrate cyclohexene in the presence of [(TMP)MnCl] ( 1 a ) with electron‐donating substituents, the ratio of heterolysis to homolysis increased gradually in all solvent systems, suggesting that [(TMP)Mn? OOC(O)R] species 2 a is the major active species. When the substrate was changed from the easy‐to‐oxidize one (cyclohexene) to difficult‐to‐oxidize ones (1‐octene and ethylbenzene), the ratio of heterolysis to homolysis increased a little or did not change. [(F₂₀TPP)Mn? OOC(O)R] species 2 b generated from the reaction of [(F₂₀TPP)MnCl] ( 1 b ) with electron‐withdrawing substituents and PPAA also gradually becomes involved in olefin epoxidation (although to a much lesser degree than with [(TMP)Mn? OOR] 2 a ) depending on the concentration of the easy‐to‐oxidize substrate cyclohexene in all aprotic solvent systems except for CH₃CN, whereas Mn^V?O species is the major active oxidant in the protic solvent system. With difficult‐to‐oxidize substrates, the ratio of heterolysis to homolysis did not vary except for 1‐octene in toluene, indicating that a Mn^V?O intermediate generated from the heterolytic cleavage of 2 b becomes a major reactive species. We also studied the competitive epoxidations of cis‐2‐octene and trans‐2‐octene with two manganese(III) porphyrin complexes by meta‐chloroperbenzoic acid (MCPBA) in various solvents under catalytic reaction conditions. The ratios of cis‐ to trans‐2‐octene oxide formed in the reactions of MCPBA varied depending on the substrate concentration, further supporting the contention that the reactions of manganese porphyrin complexes with peracids generate multiple reactive oxidizing intermediates.     

Manganese(III)-carboxylate binding: Chemistry and structure of a hydrated pyridinedicarboxylate

The reaction of Mn(CH₃COO)₃ 2H₂O with the carboxyl-rich ligand pyridine-2,6-dicarboxylic acid (H₂L) in methanol affords a high-spin (S = 2) hydratedbis-complex. Structure determination has revealed the solid to be [Mn^III(H₂ L)(L)] [Mn^IIIL₂] 5H₂ O: space group P−1;Z = 2;a = 7.527(3)?³,b= 14.260(4)?,c = 16.080(6)?,α = 91.08(3)°,β = 103.58(3)°,γ= 105.41(3)° andV= 1611.2(10)?³. Each ligand is planar and is bonded in the tridentate O₂N fashion. The MnO₄N₂ coordination spheres show large distortions from octahedral symmetry. The lattice is stabilised by an extensive network of O…O hydrogen-bonding involving water molecules and carboxyl functions. Upon dissolution in water, protic redistribution occurs and the complex acts as the mono-basic acid Mn(HL)(L) (pK, 4.3 ±0.05). The deprotonated complex displays high metal reduction potentials: Mn^IVL₂-Mn^IIIL ₂ ⁻ , 1.05V; Mn^IIIL ₂ ⁻ Mn^IIL ₂ ²⁻ -, 0.28V vs. SCE     

Syntheses and structural determinations of the nine-coordinate rare earth metal: Na4[DyIII(dtpa)(H2O)]2·16H2O,Na[DyIII(edta)(H2O)3]·3.25H2O and Na3[DyIII(nta)2(H2O)]·5.5H2O

Three complexes, Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O, Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O and Na₃[Dy^III (nta)₂(H₂O)]?·?5.5H₂O, have been synthesized in aqueous solution and characterized by FT–IR, elemental analyses, TG–DTA and single-crystal X-ray diffraction. Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O crystallizes in the monoclinic system with P2₁/n space group, a?=?18.158(10)?Å, b?=?14.968(9)?Å, c?=?20.769(12)?Å, β?=?108.552(9)°, V?=?5351(5)?ų, Z?=?4, M?=?1517.87?g?mol^?1, D _c?=?1.879?g?cm^?3, μ?=?2.914?mm^?1, F(000)?=?3032, and its structure is refined to R ₁(F)?=?0.0500 for 9384 observed reflections [I?>?2σ(I)]. Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O crystallizes in the orthorhombic system with Fdd2 space group, a?=?19.338(7)?Å, b?=?35.378(13)?Å, c?=?12.137(5)?Å, β?=?90°, V?=?8303(5)?ų, Z?=?16, M?=?586.31?g?mol^?1, D _c?=?1.876?g?cm^?3, μ?=?3.690?mm^?1, F(000)?=?4632, and its structure is refined to R ₁(F)?=?0.0307 for 4027 observed reflections [I?>?2σ(I)]. Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O crystallizes in the orthorhombic system with Pccn space group, a?=?15.964(12)?Å, b?=?19.665(15)?Å, c?=?14.552(11)?Å, β?=?90°, V?=?4568(6)?ų, Z?=?8, M?=?724.81?g?mol^?1, D _c?=?2.102?g?cm^?3, μ?=?3.422?mm^?1, F(000)?=?2848, and its structure is refined to R ₁(F)?=?0.0449 for 4033 observed reflections [I?>?2?σ(I)]. The coordination polyhedra are tricapped trigonal prism for Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O and Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O, but monocapped square antiprism for Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O. The crystal structures of these three complexes are completely different from one another. The three-dimensional geometries of three polymers are 3-D layer-shaped structure for Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O, 1-D zigzag type structure for Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O and a 2-D parallelogram for Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O. According to thermal analyses, the collapsing temperatures are 356°C for Na₄[Dy^III(dtpa)(H₂O)]₂?·?16H₂O, 371°C for Na[Dy^III(edta)(H₂O)₃]?·?3.25H₂O and 387°C for Na₃[Dy^III(nta)₂(H₂O)]?·?5.5H₂O, which indicates that their crystal structures are very stable.     

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].     

Synthesis,crystal structures,and magnetic properties of methoxido-bridged dinuclear MnIII complexes derived from tri-dentate chelating ligands

Two new doubly methoxido-bridged Mn^III dinuclear complexes, [Mn^III(mphp)(μ-OCH₃)(CH₃OH)]₂·2CH₃OH (1) and ([Mn^III(ahbz)(μ-OCH₃)(CH₃OH)]₂·2CH₃OH (2), have been synthesized by using the tridentate ligands H₂mphp (H₂mphp = 2-methyl-6-(pyrimidin-2-yl-hydrazonomethyl)-phenol) and H₂ahbz (H₂ahbz = N-(2-amino-propyl)-2-hydroxy-benzamide). The complexes have been characterized by single-crystal X-ray diffraction analysis and magnetic measurements. Complexes 1 and 2 have a similar dimeric molecular structure. Two [Mn(L)(CH₃OH)]⁺ moieties (L^2? = mphp^2? or ahbz^2?) are bridged by two μ-OCH₃^? groups in the axial-equatorial asymmetric manner. The coordination geometry of Mn^III is an axially elongated octahedron with two oxygens of a methanol ligand and a methoxido ligand situated at the axial positions. Magnetic measurements indicate that 1 and 2 exhibit antiferromagnetic behavior with the fitting parameter of J = ?1.49(3) cm^?1, D = ?1.3(1) cm^?1, g = 1.98(1) and zJ′ = ?0.18(4) cm^?1 for 1, and J = ?1.6(2) cm^?1, D = 4.5(3) cm^?1, g = 2.06(1) and zJ′ = 1.4(1) cm^?1 for 2 on the basis of the spin Hamiltonian ? = ?2J?_Mn1?_Mn2.     

Synthesis and spectral studies on heterobimetallic complexes of manganese and ruthenium derived from N-(2-hydroxynaphthalen-1-yl)methylenebenzoylhydrazide

The complex [Mn^IV(napbh)₂] (napbhH₂ = N-(2-hydroxynaphthalen-1-yl)methylenebenzoylhydrazide) reacts with activated ruthenium(III) chloride in methanol in 1 : 1.2 molar ratio under reflux, giving heterobimetallic complexes, [Mn^IV(napbh)₂Ru^IIICl₃(H₂O)] · [Ru^III(napbhH)Cl₂(H₂O)] reacts with Mn(OAc)₂·4H₂O in methanol in 1 : 1.2 molar ratio under reflux to give [Ru^III(napbhH)Cl₂(H₂O)Mn^II(OAc)₂]. Replacement of aquo in these heterobimetallic complexes has been observed when the reactions are carried out in the presence of pyridine (py), 3-picoline (3-pic), or 4-picoline (4-pic). The molar conductances for these complexes in DMF indicates 1 : 1 electrolytes. Magnetic moment values suggest that these heterobimetallic complexes contain Mn^IV and Ru^III or Ru^III and Mn^II in the same structural unit. Electronic spectral studies suggest six coordinate metal ions. IR spectra reveal that the napbhH₂ ligand coordinates in its enol form to Mn^IV and bridges to Ru^III and in the keto form to Ru^III and bridging to Mn^II.     

Cyano‐Bridged MnIII?MIII Single‐Chain Magnets with MIII=CoIII,FeIII, MnIII,and CrIII

A series of isostructural cyano‐bridged Mn^III(h.s.)–M^III(l.s.) alternating chains, [Mn^III(5‐TMAMsalen)M^III(CN)₆] ? 4H₂O (5‐TMAMsalen^2?=N,N′‐ethylenebis(5‐trimethylammoniomethylsalicylideneiminate), Mn^III(h.s.)=high‐spin Mn^III, M^III(l.s.)=low‐spin Co^III, Mn? Co ; Fe^III, Mn? Fe ; Mn^III, Mn? Mn ; Cr^III, Mn? Cr ) was synthesized by assembling [Mn^III(5‐TMAMsalen)]³⁺ and [M^III(CN)₆]^3?. The chains present in the four compounds, which crystallize in the monoclinic space group C2/c, are composed of an [‐Mn^III‐NC‐M^III‐CN‐] repeating motif, for which the ‐NC‐M^III‐CN‐ motif is provided by the [M^III(CN)₆]^3? moiety adopting a trans bridging mode between [Mn^III(5‐TMAMsalen)]³⁺ cations. The Mn^III and M^III ions occupy special crystallographic positions: a C₂ axis and an inversion center, respectively, forming a highly symmetrical chain with only one kind of cyano bridge. The Jahn–Teller axis of the Mn^III(h.s.) ion is perpendicular to the N₂O₂ plane formed by the 5‐TMAMsalen tetradentate ligand. These Jahn–Teller axes are all perfectly aligned along the unique chain direction without a bending angle, although the chains are corrugated with an Mn‐N_axis‐C angle of about 144°. In the crystal structures, the chains are well separated with the nearest inter‐chain M???M distance being relatively large at 9 Å due to steric hindrance of the bulky trimethylammoniomethyl groups of the 5‐TMAMsalen ligand. The magnetic properties of these compounds have been thoroughly studied. Mn? Fe and Mn? Mn display intra‐chain ferromagnetic interactions, whereas Mn? Cr is characterized by an antiferromagnetic exchange that induces a ferrimagnetic spin arrangement along the chain. Detailed analyses of both static and dynamic magnetic properties have demonstrated without ambiguity the single‐chain magnet (SCM) behavior of these three systems, whereas Mn? Co is merely paramagnetic with S_Mn=2 and D/k_B=?5.3 K (D being a zero‐field splitting parameter). At low temperatures, the Mn? M compounds with M=Fe, Mn, and Cr display remarkably large M versus H hysteresis loops for applied magnetic fields along the easy magnetic direction that corresponds to the chain direction. The temperature dependence of the associated relaxation time for this series of compounds systematically exhibits a crossover between two Arrhenius laws corresponding to infinite‐chain and finite‐chain regimes for the SCM behavior. These isostructural hetero‐spin SCMs offer a unique series of alternating [‐Mn‐NC‐M‐CN‐] chains, enabling physicists to test theoretical SCM models between the Ising and Heisenberg limits.     

Crystal structure of a cyanide-bridged heptanuclear manganese(III)–chromium(III) complex with a ground state S = 21/2

K₃[Cr(CN)₆] reacts with the mononuclear Mn^III complex Mn(salen)ClO₄ · 2H₂O [salen: N,N-ethylenebis(salicylideneiminato)dianion] to give a bimetallic heptanuclear complex cation salt [Cr{(CN)Mn(salen · H₂O)}₆][Cr(CN)₆]6H₂O. In the complex anion, [Cr{(CN)Mn(salen · H₂O)}₆]³⁺, six Mn^III ions coordinate to a Cr^III center via cyano bridges, forming a spherical species with 3 symmetry. A study of magnetic properties shows the presence of antiferromagnetic interaction through the cyanide bridge between Cr^III (S = 3/2) and Mn^III (S = 4/2) and results in a ground state S = 21/2.     

Homo‐ and Heterovalent Polynuclear Cerium and Cerium/Manganese Aggregates

Reactions of Ce^III(NO₃)₃?6 H₂O or (NH₄)₂[Ce^IV(NO₃)₆] with Mn‐containing starting materials result in seven novel polynuclear Ce or Ce/Mn complexes with pivalato (^tBuCO ) and, in most cases, auxiliary N,O‐ or N,O,O‐donor ligands. With nuclearities ranging from 6–14, the compounds present aesthetically pleasing structures. Complexes [Ce^IV₆(μ₃‐O)₄(μ₃‐OH)₄(μ‐O₂C^tBu)₁₂] ( 1 ), [Ce^IV₆Mn^III₄(μ₄‐O)₄(μ₃‐O)₄(O₂C^tBu)₁₂(ea)₄(OAc)₄]?4 H₂O?4 MeCN (ea^?=2‐aminoethanolato; 2 ), [Ce^IV₆Mn^III₈(μ₄‐O)₄(μ₃‐O)₈(pye)₄(O₂C^tBu)₁₈]₂[Ce^IV₆(μ₃‐O)₄(μ₃‐OH)₄(O₂C^tBu)₁₀(NO₃)₄] [Ce^III(NO₃)₅(H₂O)]?21 MeCN (pye^?=pyridine‐2‐ethanolato; 3 ), and [Ce^IV₆Ce^III₂Mn^III₂(μ₄‐O)₄(μ₃‐O)₄(^tbdea)₂(O₂C^tBu)₁₂(NO₃)₂(OAc)₂]?4 CH₂Cl₂ (^tbdea^2?=2,2′‐(tert‐butylimino]bis[ethanolato]; 4 ) all contain structures based on an octahedral {Ce^IV₆(μ₃‐O)₈} core, in which many of the O‐atoms are either protonated to give (μ₃‐OH)^? hydroxo ligands or coordinate to further metal centers (Mn^III or Ce^III) to give interstitial (μ₄‐O)^2? oxo bridges. The decanuclear complex [Ce^IV₈Ce^IIIMn^III(μ₄‐O)₃(μ₃‐O)₃(μ₃‐OH)₂(μ‐OH)(bdea)₄(O₂C^tBu)_9.5(NO₃)_3.5(OAc)₂]?1.5 MeCN (bdea^2?=2,2′‐(butylimino]bis[ethanolato]; 5 ) contains a rather compact Ce^IV₇ core with the Ce^III and Mn^III centers well‐separated from each other on the periphery. The aggregate in [Ce^IV₄Mn^IV₂(μ₃‐O)₄(bdea)₂(O₂C^tBu)₁₀(NO₃)₂]?4 MeCN ( 6 ) is based on a quasi‐planar {Mn^IV₂Ce^IV₄(μ₃‐O)₄} core made up of four edge‐sharing {Mn^IVCe^IV₂(μ₃‐O)} or {Ce^IV₃(μ₃‐O)} triangles. The structure of [Ce^IV₃Mn^IV₄Mn^III(μ₄‐O)₂(μ₃‐O)₇(O₂C^tBu)₁₂(NO₃)(furan)]?6 H₂O ( 7 ?6 H₂O) can be considered as {Mn^IV₂Ce^IV₂O₄} and distorted {Mn^IV₂Mn^IIICe^IVO₄} cubane units linked through a central (μ₄‐O) bridge. The Ce₆Mn₈ equals the highest nuclearity yet reported for a heterometallic Ce/Mn aggregate. In contrast to most of the previously reported heterometallic Ce/Mn systems, which contain only Ce^IV and either Mn^IV or Mn^III, some of the aggregates presented here show mixed valency, either Mn^IV/Mn^III (see 7 ) or Ce^IV/Ce^III (see 4 and 5 ). Interestingly, some of the compounds, including the heterovalent Ce^IV/Ce^III 4 , could be obtained from either Ce^III(NO₃)₃?6 H₂O or (NH₄)₂[Ce^IV(NO₃)₆] as starting material.     

A Single‐Chain Magnet Tape Based on Hexacyanomanganate(III)

The tape‐like chain {[(tptz)Mn^II(H₂O)Mn^III(CN)₆]₂Mn^II(H₂O)₂}_n?4n MeOH?2n H₂O based on the anisotropic building block hexacyanomanganate(III) exhibits long‐range magnetic ordering below 5.1 K as well as single‐chain magnetic behavior at lower temperatures with an effective energy barrier of 40.5(7) K.     

Mechanistic Insight into Peroxo‐Shunt Formation of Biomimetic Models for Compound II,Their Reactivity toward Organic Substrates,and the Influence of N‐Methylimidazole Axial Ligation

High‐valent iron‐oxo species have been invoked as reactive intermediates in catalytic cycles of heme and nonheme enzymes. The studies presented herein are devoted to the formation of compound II model complexes, with the application of a water soluble (TMPS)Fe^III(OH) porphyrin ([meso‐tetrakis(2,4,6‐trimethyl‐3‐sulfonatophenyl)porphinato]iron(III) hydroxide) and hydrogen peroxide as oxidant, and their reactivity toward selected organic substrates. The kinetics of the reaction of H₂O₂ with (TMPS)Fe^III(OH) was studied as a function of temperature and pressure. The negative values of the activation entropy and activation volume for the formation of (TMPS)Fe^IV?O(OH) point to the overall associative nature of the process. A pH‐dependence study on the formation of (TMPS)Fe^IV?O(OH) revealed a very high reactivity of OOH^? toward (TMPS)Fe^III(OH) in comparison to H₂O₂. The influence of N‐methylimidazole (N‐MeIm) ligation on both the formation of iron(IV)‐oxo species and their oxidising properties in the reactions with 4‐methoxybenzyl alcohol or 4‐methoxybenzaldehyde, was investigated in detail. Combined experimental and theoretical studies revealed that among the studied complexes, (TMPS)Fe^III(H₂O)(N‐MeIm) is highly reactive toward H₂O₂ to form the iron(IV)‐oxo species, (TMPS)Fe^IV?O(N‐MeIm). The latter species can also be formed in the reaction of (TMPS)Fe^III(N‐MeIm)₂ with H₂O₂ or in the direct reaction of (TMPS)Fe^IV?O(OH) with N‐MeIm. Interestingly, the kinetic studies involving substrate oxidation by (TMPS)Fe^IV?O(OH) and (TMPS)Fe^IV?O(N‐MeIm) do not display a pronounced effect of the N‐MeIm axial ligand on the reactivity of the compound II mimic in comparison to the OH^? substituted analogue. Similarly, DFT computations revealed that the presence of an axial ligand (OH^? or N‐MeIm) in the trans position to the oxo group in the iron(IV)‐oxo species does not significantly affect the activation barriers calculated for C?H dehydrogenation of the selected organic substrates.     

Two-step one-electron transfer reaction of chromium(III) complex containing levodopa and uridine with N-bromosuccinimide

[Cr^III(LD)(Urd)(H₂O)₄](NO₃)₂?·?3H₂O (LD?=?Levodopa; Urd?=?uridine) was prepared and characterized. The product of the oxidation reaction was examined using HPLC. Kinetics of the oxidation of [Cr^III(LD)(Urd)(H₂O)₄]²⁺ with N-bromosuccinimide (NBS) in an aqueous solution was studied spectrophotometrically, with 1.0–5.0?×?10^?4?mol?dm^?3 complex, 0.5–5.0?×?10^?2?mol?dm^?3 NBS, 0.2–0.3?mol?dm^?3 ionic strength (I), and 30–50°C. The reaction is first order with respect to [Cr^III] and [NBS], decreases as pH increases in the range 5.46–6.54 and increases with the addition of sodium dodecyl sulfate (SDS, 0.0–1.0?×?10^?3?mol?dm^?3). Activation parameters including enthalpy, ΔH*, and entropy, ΔS*, were calculated. The experimental rate law is consistent with a mechanism in which the protonated species is more reactive than its conjugate base. It is assumed that the two-step one-electron transfer takes place via an inner-sphere mechanism. A mechanism for this reaction is proposed and supported by an excellent isokinetic relationship between ΔH* and ΔS* for some Cr^III complexes. Formation of [Cr^III(LD)(Urd)(H₂O)₄]²⁺ in vivo probably occurs with patients who administer the anti-Parkinson drug (Levodopa), since Cr^III is a natural food element. This work provides an opportunity to identify the nature of such interactions in vivo similar to that in vitro.     

A binuclear manganese(II) complex,deca­aqua(μ‐1,2,4,5‐benzene­tetra­carboxyl­ato‐O1:O4)­di­manganese(II) hydrate

In the title Mn^II complex, [Mn₂(C₁₀H₂O₈)(H₂O)₁₀]·H₂O, two independent binuclear mol­ecules bridged by the 1,2,4,5‐benzene­tetra­carboxyl anion exist in a unit cell, with each anion lying about an inversion centre. One of the Mn—O_water distances [2.2922 (13) Å] is significantly longer than the Mn^II—O_water distances reported so far for Mn^II complexes and very close to the Mn—O_water distances found in the axial direction of Mn^III complexes.     

Synthesis and structural determination of the first eight-coordinate rare earth metal complex with a six-member ring, (NH4)[EuIII(pdta)(H2O)] · H2O

(NH₄)[Eu^III(pdta)(H₂O)]?·?H₂O has been synthesized and characterized by infrared spectrum, fluorescence spectrum, elemental analyses and single-crystal X-ray diffraction techniques. It crystallizes in the monoclinic system with space group P2₁/n, a?=?12.7700(15)?Å, b?=?9.3885(11)?Å, c?=?14.4070(18)?Å, α?=?90°, β?=?95.950(2)°, γ?=?90°, V?=?1718.0(4)?ų, Z?=?4, M?=?508.28, D _c?=?1.965?g?cm^?3, μ?=?3.708?mm^?1, F(000)?=?1108. The structure was refined to R ₁?=?0.0238 for 3469 observed reflections (I?>?2σ(I)). The Eu^IIIN₂O₆ part in the [Eu^III(pdta)(H₂O)]^? complex anion has an eight-coordinate structure with a distorted square anti-prismatic conformation, in which six coordination positions, two nitrogen atoms and four oxygen atoms are from one pdta (=propylenediaminetetraacetic acid) ligand, the seventh position is an oxygen (O(8A)) from another pdta and the eighth coordination site is occupied by a water molecule. (NH₄)[Eu^III(pdta)(H₂O)]?·?H₂O is the first eight-coordinate complex with a six-member ring in the rare earth metal complexes with aminopolycarboxylic acid ligands.     

Complexes of chromium(III) and manganese(II) with N-naphthylideneamino acids

Summary New Cr^III and Mn^II complexes of N-naphthylideneamino acids were prepared and characterized by elemental analysis, conductance measurements, electronic and i.r. spectra. The complexes are six coordinate with the general formulae Cr(naph:AA)₂ and Mn(naph:AA)₂·2H₂O; the ligands act as mono- and/or divalent tridentate Schiff bases in an octahedral structure.