Synthesis, spectroscopy and redox properties of mononuclear manganese(II) and manganese(IV) complexes with N-(aryl)-pyridine-2-aldimine (L) and its amide derivatives. X-ray structural characterization of [Mn(MeL)2(NCS)2] (MeL = N-(4-methylphenyl)-pyridine-2-aldimine)

A series of mononuclear Mn^II and Mn^IV complexes of general formulae [MnL₂(NCS)₂] (1a–1d) and [Mn(L)₂(NCS)₂] (2a–2c) have been prepared where L are Schiff bases obtained by the condensation of pyridine-2-aldehyde with para-alkyl-substituted aniline, and L are the corresponding amide ligands. The room temperature magnetic susceptibility data of (1a–1d) indicate that Mn^II is in a high spin state. The cyclic voltammograms of (1a–1d) exhibit a one-electron quasi-reversible Mn^IIMn^III oxidation. A linear correlation has been found when E⁰[Mn^III/Mn^II] is plotted against Hammett _p parameters. X-ray crystallographic data of (1b) shows that the central Mn^II ion adopts a distorted octahedral geometry with six different Mn–N distances. Upon oxidation of Mn^II complexes (1b–1d) by H₂O₂, the corresponding Mn^IV complexes (2a–2c) were obtained, and the Schiff base ligands were oxidized to the corresponding amides. The lowest energy LMCT bands of these Mn^IV complexes correlate linearly with Hammett _p parameters. The redox behavior of the Mn^IV complexes has been investigated by cyclic voltammetry. E.p.r. spectra of the Mn^II and Mn^IV complexes are also reported.     

Oxalate-bridged mixed-valence trinuclear manganese(II)-manganese(III)-manganese(II) complexes: synthesis and magnetism

Summary Two novel Mn^II-Mn^III-Mn^II oxalato complexes have been synthesized and characterized, namely [Mn₂Mn(ox)₃(L)₄](ClO₄) [L = 1,10-phenanthroline (phen) or 5-nitro-1,10-phenanthroline (NO₂-phen), respectively], where ox stands for the oxalate dianion. Based on i.r., elemental analyses and electronic spectra, these complexes are proposed to have extended oxalatobridged structures consisting of Mn^II and Mn^III ions, in which Mn^III and each Mn^II ion has a distorted octahedral environment. The temperature dependence of magnetic susceptibility for [Mn₂Mn(ox)₃(phen)₄] (ClO₄) was measured over the 4.1–300 K range and the observed data were successfully simulated by an equation based on the spin-Hamiltonian operator ( = -2J( _{1 2} + _{2 3})), giving the exchange integral J = -1.57cm^–1. This indicates weak antiferromagnetic spin exchange interaction between Mn^II and Mn^III ions.     

Synthesis,crystal structure,and magnetic characterization of two manganese Schiff-base-containing complexes

The reactions of [Mn^III(3-MeOSalen)(H₂O)₂]⁺ (Salen = N,N-ethylenebis(salicylideneaminato) dianion) with (Et₄N)₄[M(CN)₈] (M = Mo, W) have been investigated and one mononuclear manganese(II) complex [Mn^II(Salen)(H₂O)] (I) and one bimetallic ion-pair complex [Mn^III(3-MeO-Salen)(H₂O)₂]₄[W(CN)₈] · DMSO · 4H₂O (II) were obtained unexpectedly and characterized by element and single crystal structure analysis. Single crystal X-ray diffraction (CIF files CCDC nos. 1456365 (I) and 1456366 (II)) showed that the Mn²⁺ ion in complex I is five-coordinated involving in a distorted square pyramid. Furthermore, with the help of the intermolecular hydrogen bond interactions, this complex can be constructed into interesting one-dimensional zig-zag chain structure. For complex II, the coordination sphere of Mn³⁺ ion is an elongated octahedron. Additional, the four mononuclear manganese(III) units are self-complementary through the coordinated aqua ligand from one molecule and the free O(4) compartment from the neighboring molecule, giving supramolecular dimmers structure. Investigation of the magnetic susceptibility of the two complexes reveals the overall weak antiferromagnetic interactions between the adjacent manganese centers caused by H-bond interactions.     

Synthesis and characterization of complexes of the first transition series cations with 2,2′-biimidazole and 2,2′-biimidazolate

Mononuclear [M(hfacac)₂(H₂biim)] complexes, where M = Mn^II, Fe^II, Co^II, Ni^II, Cu^II or Zn^II, hfacac = hexafluoroacetylacetonate, H₂biim = 2,2-biimidazole; dinuclear K₂[M₂(acac)₄(-biim)] (M = Cu^II or Zn^II) and tetranuclear K₂[M₄(acac)₈( ₄-biim)] (M = Co^II or Ni^II) complexes have been prepared and characterized by chemical analysis, conductance measurements, i.r., electronic and e.p.r. spectroscopies and by magnetic susceptibility measurements (in the 2–300 K range). Mn^II, Fe^II and Co^II are in a high spin state. The e.p.r. spectra of Cu^II and Mn^II compounds have been recorded.     

Binuclear and mononuclear cobalt(II), nickel(II) and copper(II) complexes of 4,4′-bis(alkylaminoisonitrosoacetyl)diphenyl-methane derivatives

4,4-Bis(chloroacetyl)diphenylmethane has been prepared from ClCH₂COCl and Ph₂CH₂. 4,4-Methylenebis(phenylglyoxylohydroximoyl chloride has also been obtained. Four new substituted 4,4-bis(alkylaminoisonitrosoacetyl)diphenylmethanes (ligands) have been prepared from 4,4-methylenebis(phenylglyoxylohydroximoyl chloride) and the corresponding amines. The Ni^II, Cu^II and Co^II complexes of these ligands were prepared and their structures were identified using AAS, i.r., ¹H-n.m.r. spectral data, elemental analyses and magnetic susceptibility measurements.     

Synthesis,structures, and magnetic properties of two closely-related manganese(II) coordination polymers

The reactions of Mn²⁺ ion with 4-nitrobenzene-1,2-bicarboxylic acid in the presence of bipyridyl-type coligands gave two new manganese(II) coordination polymers, [Mn₂(Nbdc)₂(Bipyp)(H₂O)₄] _n (I) and [Mn₂(Nbdc)₂(Bipye)(H₂O)₄] _n (II) (H₂Nbdc = 4-nitrobenzene-1,2-bicarboxylic acid, Bipyp = 1,3-bi(4-pyridyl)propane, and Bipye = 1,2-bi(4-pyridyl)ethane). Both two complexes contain uniform carboxyl-bridged manganese chains with the composition of [Mn₂(Nbdc)₂(H₂O)₄] _n , which are interlinked by interchain Bipyp/Bipye spacers to afford two closely-related layers (CIF files CCDC nos. 1008182 (I) and 1008183 (II)). Magnetic studies for two compounds show the presence of similar antiferromagnetic couplings between the adjacent Mn²⁺ ions through the carboxyl bridges, the best fittings to the experimental magnetic susceptibilities gave J =–0.20 cm^–1 and g = 1.96 for I, and J =–0.24 cm^–1 and g = 1.98 for II. Similar magnetic parameters and thermal behaviors further verify that two compounds possess closely-related structures.     

A New Mixed‐Valence Tetranuclear Manganese [MnII2MnIII2] Cluster

A new tetranuclear manganese complex [Mn₂^IIMn₂^III(bhmcpH)₂(hmp)₄Cl₂(MeOH)₂] ( 1 ) [bhmcpH₃ = 2, 6‐bis(hydroxymethyl)‐4‐chlorophenol, hmpH = 2‐(hydroxymethyl)pyridine] was synthesized and characterized. X‐ray diffraction analyses reveal that complex 1 crystallizes in the monoclinic space group P2₁/c. It has a mixed‐valence tetranuclear dicubane unit, which comprises two Mn^II and two Mn^III ions. The temperature dependence of the magnetic susceptibilities of 1 indicates ferromagnetic interactions between the manganese ions.     

A mixed‐valence diacetate‐bridged MnII–MnIII complex incorporating a bridging phenolate ligand

The synthesis and characterization of a new unsymmetrical dinucleating N,O‐donor ligand, 2‐[N,N‐bis­(2‐pyridyl­methyl)­amino­methyl]‐6‐[N‐(3,5‐di‐tert‐butyl‐2‐oxidobenzyl)‐N‐(2‐pyridyl­amino)­aminomethyl]‐4‐methyl­phenol (H₂Ldtb), as well as the X‐ray crystal structure of its corresponding mixed‐valence diacetate‐bridged manganese complex, di‐μ‐acetato‐μ‐{2‐[N,N‐bis­(2‐pyridylmethyl)amino­methyl]‐6‐[N‐(3,5‐di‐tert‐butyl‐2‐oxidobenzyl)‐N‐(2‐pyridyl­amino)­aminomethyl]‐4‐methylphenolato}dimanganese(II,III) tetra­phenyl­borate, [Mn^IIMn^III(C₄₂H₄₉N₅O₂)(C₂H₃O₂)₂](C₂₄H₂₀B), are reported. The complex may be regarded as an inter­esting structural model for the mixed‐valence Mn^II–Mn^III state of manganese catalase.     

Tetranuclear Manganese Complex Incorporating 2‐Pyridyloximate Ligand: Synthesis,Crystal Structure and Magnetic Property

A tetranuclear manganese complex of the composition {Mn₄[(Py)C(Ph)NO]₄(CH₃CH₂OH)₃(CH₃CH₂O)Cl₃}·2H₂O ( 1 ) was synthesized by solvothermal reaction, and characterized by X‐ray single crystal diffraction, IR spectroscopy, and elemental analysis. X‐ray analysis revealed that complex 1 contains a [Mn₄(NO)₄]⁴⁺ core with three Mn^II atoms displaying distorted octahedral arrangements and one Mn^II ion exhibiting a trigonal bipyramidal arrangement. Low‐temperature magnetic susceptibility measurement for the solid sample of 1 revealed antiferromagnetic Mn^II ··· Mn^II interactions.     

Mononuclear manganese(II) and manganese(III) complexes of N<Subscript>2</Subscript>O donors involving amine and phenolate ligands: absorption spectra,electrochemistry and crystal structure of [Mn(L<Subscript>3</Subscript>)<Subscript>2</Subscript>](ClO<Subscript>4</Subscript>)

A number of mononuclear manganese(II) and manganese(III) complexes have been synthesized from tridentate N₂O aminophenol ligands (HL₁–HL₅) formed by reduction of corresponding Schiff bases with NaBH₄. Three types of tridentate N₂O aminophenols have been prepared by reducing with NaBH₄which are (a) Schiff bases obtained by bromo salicylaldehyde reaction with N,N-dimethyl/N,N-diethyl ethylene diamine (HL₁, HL₂), (b) Schiff bases obtained by condensing salicylaldehyde/bromo salicylaldehyde and picolyl amine (HL₃, HL₄), (c) pyridine-2-aldehyde and 2-aminophenol (HL₅). All the manganese complexes have been prepared by direct addition of manganese perchlorate to the corresponding ligands and were characterized by the combination of i.r., u.v.–vis spectroscopy, magnetic moments and electrochemical studies. The u.v.–vis spectra of all of the manganese(III) complexes show two weak d–d transitions in the 630–520 nm region, which support a distorted octahedral geometry. The electron transfer properties of all of the manganese(III) complexes (1–4 and 6) exhibit mostly similar characteristics consisting two redox couples corresponding to the Mn^III → Mn^II reductions and Mn^III → Mn^IV oxidations. The electronic effect on the potential has also been studied by changing different substituents in the ligands. In all cases, an electron-donating group stabilizes the higher oxidation state and electron withdrawing group prefers the lower oxidation state. The cyclic voltammogram of [Mn^II(L₅)₂] shows an irreversible oxidation Mn^II → Mn^III at −0.88 V, followed by another quasi-reversible oxidation Mn^III → Mn^IV at +0.48 V. The manganese(III) complex (3) [Mn(L₃)₂]ClO₄has been characterized by X-ray crystallography.     

Synthesis,crystal structure and properties of a tetrametallic 3-ferrocenyl-2-crotonic acid-bridged manganese(II) complex [Mn2(phen)4(FCA)2](ClO4)2·H2O

The title complex [Mn₂(phen)₄(FCA)₂](ClO₄)₂·H₂O (1) (FCA = dianion of 3-ferrocenyl-2-crotonic acid, phen = 1,10-phenanthroline) has been prepared, and its structure determined by single crystal X-ray diffraction analysis. The structure consists of a dinuclear cation [Mn₂(phen)₄(FCA)₂]²⁺, non-coordinated perchlorate anions and a water molecule. The two Mn^II ions are separated by 4.374 Å in the cation and are dicarboxylate-bridged by carboxylate ligands containing ferrocenyl units. Each FCA is bound to two Mn^II ions through carboxylate oxygens with the syn–anti bridging mode. The Mn^II ion is coordinated in an octahedral N₄O₂ geometry by two chelate phen ligands and two -carboxylate oxygen atoms. Electrochemical properties of (1) are discussed.     

Structure and Magnetic Ordering of the Anomalous Layered (2D) Ferrimagnet [NEt4]2MnII3(CN)8 and 3D Bridged‐Layered Antiferromagnet [NEt4]MnII3(CN)7 Prussian Blue Analogues

The reaction of Mn^II and [NEt₄]CN leads to the isolation of solvated [NEt₄]Mn₃(CN)₇ ( 1 ) and [NEt₄]₂Mn₃(CN)₈ ( 2 ), which have hexagonal unit cells [ 1 : R$\bar 3$ m, a=8.0738(1), c=29.086(1) Å; 2 : P$\bar 3$ m1, a=7.9992(3), c=14.014(1) Å] rather than the face centered cubic lattice that is typical of Prussian blue structured materials. The formula units of both 1 and 2 are composed of one low‐ and two high‐spin Mn^II ions. Each low‐spin, octahedral [Mn^II(CN)₆]^4? bonds to six high‐spin tetrahedral Mn^II ions through the N atoms, and each of the tetrahedral Mn^II ions are bound to three low‐spin octahedral [Mn^II(CN)₆]^4? moieties. For 2 , the fourth cyanide on the tetrahedral Mn^II site is C bound and is terminal. In contrast, it is orientationally disordered and bridges two tetrahedral Mn^II centers for 1 forming an extended 3D network structure. The layers of octahedra are separated by 14.01 Å (c axis) for 2 , and 9.70 Å (c/3) for 1 . The [NEt₄]⁺ cations and solvent are disordered and reside between the layers. Both 1 and 2 possess antiferromagnetic superexchange coupling between each low‐spin (S=1/2) octahedral Mn^II site and two high‐spin (S=5/2) tetrahedral Mn^II sites within a layer. Analogue 2 orders as a ferrimagnet at 27(±1) K with a coercive field and remanent magnetization of 1140 Oe and 22 800 emuOe mol^?1, respectively, and the magnetization approaches saturation of 49 800 emuOe mol^?1 at 90 000 Oe. In contrast, the bonding via bridging cyanides between the ferrimagnetic layers leads to antiferromagnetic coupling, and 3D structured 1 has a different magnetic behavior to 2 . Thus, 1 is a Prussian blue analogue with an antiferromagnetic ground state [T_c=27 K from d(χT)/dT].     

Complexes of 2-(2-hydroxyacetophenone)imino-5-(p-anisyl)-1,3,4-oxadiazole with some bivalent metals ions

Summary The metal complexes of the type [M(SB)₂(H₂O)₂] and [M(SB)₂][where M = Mn^II, Co^II, Ni^II or Cu^II, M = Zn^II Cd^II, Hg^II and Pb^II and SBH = 2-(2-hydroxyacetophenone)imino-5-(p-anisyl)-1,3,4-oxadiazole] have been prepared and characterised by elemental analyses, thermal analyses, magnetic measurements, electronic and infrared spectral studies. The complexes [M(SB)₂(H₂O)₂] possess octahedral structures, whereas complexes [M(SB)₂] are tetrahedral. The crystal field parameters of the Co^II and Ni^II complexes are also calculated.     

New approach to the synthesis of polynuclear heterometallic pivalates with iron and manganese atoms

New hexanuclear Fe(III)–Mn(II, III) pivalates [Fe₂ ^III Mn₄ ^II(O)₂(Piv)₁₀(HPiv)₄] (I) or [Fe₄ ^III Mn₂ ^III(O)₂(Piv)₁₂(CH₂O₂)(HPiv)₂] · Et₂O (II) are synthesized using the solid-state thermolysis of [Fe₂Mn(O)(Piv)₆(HPiv)₃] (90°С). Complexes I and II differ by the ratio of iron and manganese ions, which depends on the atmospheric composition during thermolysis. The structures of compounds I and II are determined by X-ray diffraction studies. According to the parameters of the Mössbauer spectrum, complex I contains the Fe³⁺ ions in the high-spin state in the octahedral environment of oxygen atoms.     

Two new clusters with MnII-MnIV magnetic exchange from the use of polyalcohol ligands

Two mixed-valence Mn(II,IV) complexes, [Mn^II₄Mn^IV₃(teaH)₃(tea)(thmeH)₃(thme)](ClO₄)₂·3MeCN (1) and [Mn^II₂Mn^IV₂(edteH)₂(peolH)₂]·4MeOH (2), where H₄edte = N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine, teaH₃ = tris(2-hydroxyethyl)amine, H₄peol = pentaerythritol, and H₃thme = 1,1,1-tris(hydroxymethyl)ethane, were prepared from the corresponding manganese salts and mixed ligands with polyalcohols. The two clusters consist of a trapped-valence polynuclear core comprising 4Mn^II and 3Mn^IV for 1, 2Mn^II and 2Mn^IV ions for 2. Complex 1 crystallizes in the rhombohedral space group R3c, while 2 crystallizes in the monoclinic space group P2₁/c. Complex 1 consists of a near-planar Mn₇ unit that comprises a Mn₆ hexagon of alternating Mn^II and Mn^IV ions surrounding a central Mn^II ion. The remaining coordinated sites are occupied by eight different deprotonation degrees of H₃tea or H₃thme. The tetranuclear cluster of 2 consists of a fused defective dicubane Mn₄O₆ core, and the four Mn ions are coordinated by oxygens from edteH^3? and peolH^3? into an unusual butterfly-like [Mn^II₂Mn^IV₂] topology. The two clusters are also characterized by mass spectra and X-ray photoelectron spectroscopy. Direct current magnetization studies reveal ferromagnetic interactions within both Mn clusters.     

Valence Tautomerism in a o-Benzoquinone Adduct of a Tetraazamacrocycle Complex of Manganese

Two different charge distributions of the complex cation [Mn^III(cth)(diox)]⁺ (cth=a tetraazamacrocycle, diox=3,5-di-tert-butyl-o-benzoquinone; structure shown in the picture) can be isolated by varying the counteranion: [Mn^III(cth)(cat)]BPh₄ and [Mn^II(cth)(sq)]ClO₄ (cat and sq denote the catecholato and semiquinonato forms of the ligand). The complex undergoes noncooperative entropy-driven valence tautomeric transitions.     

Anomalous Stoichiometry and Antiferromagnetic Ordering for the Extended Hydroxymanganese(II) Cubes/Hexacyanometalate-Based 3D-Structured [MnII4(OH)4][MnII(CN)6](OH2)6⋅H2O

The reaction of Mn^II(O₂CMe)₂ and NaCN or LiCN in water forms a light green insoluble material. Structural solution and Rietveld refinement of high-resolution synchrotron powder diffraction data for this unprecedented, complicated compound of previously unknown composition revealed a new alkali-free ordered structural motif with [Mn^II₄(μ₃-OH)₄]⁴⁺ cubes and octahedral [Mn^II(CN)₆]⁴⁻ ions interconnected in 3D by Mn^II-N≡C-Mn^II linkages. The composition is {[Mn^II(OH₂)₃][Mn^II(OH₂)]₃}(μ₃-OH)₄][Mn^II(μ-CN)₂(CN)₄] ⋅ H₂O=[Mn^II₄(μ₃-OH)₄(OH₂)₆][Mn^II(μ-CN)₂(CN)₄] ⋅ H₂O, which is further simplified to [Mn₄(OH)₄][Mn(CN)₆](OH₂)₇ ( 1 ). 1 has four high-spin (S=5/2) Mn^II sites that are antiferromagnetically coupled within the cube and are antiferromagnetically coupled to six low-spin (S=1/2) octahedral [Mn^II(CN)₆]⁴⁻ ions. Above 40 K the magnetic susceptibility, χ(T), can be fitted to the Curie–Weiss expression, χ ∝(T−θ)⁻¹, with θ=−13.4 K, indicative of significant antiferromagnetic coupling and 1 orders as an antiferromagnet at T_c=7.8 K.     

Synthesis,spectral and thermal studies of monomeric,homobimetallic and polymeric complexes containing benzoyldithiocarbazate

New mixed ligand complexes of benzoyldithiocarbazate (H₂BDT) have been synthesized and characterized by elemental analyses, spectral studies (i.r., u.v.–vis., mass), thermal analysis and electrical conductivity measurements. The complexes have the general formulae: [M₂(BDT)(OX)₂] · xH₂O; [Co₂(BDT)(OX)₂(H₂O)₄]; [M(HBDT)(OX)-(H₂O)], [Ni(BDT)(py)₂] _n and [Ni(BDT)(L)] _n where M = Mn^II, Ni^II and Cu^II; BDT = dithiocarbazate dianion; OX = 8-hydroxyquinolinate; x = 1 or 2; M = Zn^II or Cd^II; HBDT = dithiocarbazate anion and L = 2,2-bipyridyl or 1,10-o-phenanthroline. For the [M₂(BDT)(OX)₂] · xH₂O, [Co₂(BDT)(OX)₂(H₂O)₄], [Ni(BDT)(py)₂] _n and [Ni(BDT)(L)] _n complexes, benzoyldithiocarbazate acts as a dibasic-tetradentate ligand in the enol form via the enolic oxygen, the hydrazide nitrogens and the thiolate sulphur, while it acts as a monobasic-tridentate ligand in the keto form in the [M(HBDT)(OX)(H₂O)] complexes. The thermal behaviour of the complexes has been studied by t.g.–d.t.g. techniques. Kinetic parameters of the thermal decomposition process have been computed by Coats–Redfern and Horowitz–Metzger methods. It is obvious that the thermal decomposition in the complexes occurs directly at the metal–ligand bonds except for the Zn^II and Cd^II complexes in which decomposition seems to be at a point in the benzoyldithiocarbazate moiety. From the calculated kinetic data it can be concluded that the dehydration processes in all complexes have been described as phase-boundary controlled reactions. The activation energy values reveal that the thermal stabilities of the homobimetallic complexes lie in the order: Mn^II < Ni^II < Co^II, while the monomeric Cd^II complex has more enhanced thermal stability than the Zn^II complex.     

The chemistry of pyridine thiols and related ligands, Part 5. Synthesis and spectroscopy of nickel(II) and copper(II) complexes containing 1-oxopyridine-2-thione and 2,2′-bipyridine or 1,10-phenanthroline

Summary Reactions of bis(1-oxopyridine-2-thione) Ni^II or Cu^II with 2,2-bipyridine (bipy) or 1,10-phenanthroline (phen) yield complexes of stoichiometry: Ni(C₅H₄NOS)₂L {L = bipy, two isomers: (1) and (2), L = phen, one isomer (3)} and Cu(C₅H₄NOS)₂(phen)·0.75CHCl₃ (4). The spectroscopy (i.r., u.v.-vis., e.s.r.) and magnetism studies of the above complexes are described. On the basis of conductivity, the Cu^II-phen complex has been formulated as [Cu(C₅H₄NOS)(phen)₂][Cu(C₅H₄NOS)₃]·1.5CHCl₃ (4). The vis. absorption spectra support similar octahedral structures for the minor bipy isomer (2) and for the Ni^II-phen complex [(3)], whereas the major isomer [(1)] has a different structure. The e.s.r. spectrum of the Cu^II-phen complex (4) is commensurate with an elongated octahedral structure. New methods for the preparation and spectroscopy of M(C₅H₄NOS)₂ (M = Mn, Ni, Cu or Zn) compounds have been investigated.