Temperature effect on the conversions of phthalato and maleato manganese(II) complexes with diamine ligands

1,10-Phenanthroline hydrogen phthalato manganese(II) dimer [Mn₂(Hphth)₂(phen)₄] · 2Hphth · 6H₂O (1), monomeric phenanthroline phthalato manganese(II) monomer [Mn(phth)(phen)₂(H₂O)] · 2.5H₂O (2), 2,2′-bipyridine phthalato manganese(II) polymer [Mn(phth)(bpy)(H₂O)₂]_n (3) and 1,10-phenanthroline maleato polymer [Mn(male)(phen)(H₂O)₂]_n · 2nH₂O (4) (H₂phth = o-phthalic acid, male = maleic acid, phen = 1,10-phenanthroline and bpy = 2,2′-bipyridine) have been synthesized and characterized spectroscopically and structurally. Each Mn(II) atom in dimeric 1 is octahedrally coordinated by two oxygen atoms of phthalate anions and by two cis-phenanthroline ligands. The hydrogen phthalato anion bridges the Mn(II) ions through the deprotonated carboxyl groups, while the carboxylic acid group remains free. In the monomeric 2, the Mn(II) ion is octahedrally surrounded by four nitrogen atoms from two cis-phen ligands, one carboxyl oxygen from a monodentate phth ion, and one coordinated water molecule. The dimeric phthalato complex 1 can be cleaved into monomer 2 under heating with deprotonation, and the course of the reaction can be qualitatively traced by IR spectra. The phthalate group in the complex 3 binds to two manganese atoms through the vicinal carboxyl-oxygen atoms in syn-syn bridging mode. The Mn(II) atoms are linked by the phthalate group to yield a one-dimensional chain running along the a-axis. The coordination polymer 3 can be obtained from the reaction of dichloro dibipyridine manganese with phthalate under heating. In polymer 4, the manganese atom is six-coordinated by two nitrogen atoms from phen, two oxygen atoms from the coordinated water molecules and two oxygen atoms from two different maleate dianions. Each maleato unit links two neighboring manganese atoms to yield one-dimensional chain along b-axis in bis-monodentate mode. The single-chain polymer 4 prepared at low temperature can be converted to double-chain coordination polymer [Mn(male)(phen)]_n · nH₂O (5) with dehydration in warm solution.     

Syntheses, structures and magnetic properties of μ1,5-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(ClO₄/PF₆)₂·CH₃OH (1/2) and two heptacoordinated coordination polymers [Mn(L2)(dca)]_n(ClO₄/PF₆)_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 MnN₆ 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 MnN₇ 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.     

A dimanganese(II) complex with bridging chlorides: Synthesis, electrochemistry, magnetic behavior, structure and bonding

The synthesis of dimeric [Mn₂Cl₂(μ-Cl)₂(dipa)₂]·MeOH (3) (dipa = dipyridylmethylamine) from [MnCl₂(H₂O)₄] (1) and dipa (2) and its structural characterization is reported. In the solid state complex 3 is dimeric and possesses crystallographically imposed C₂ symmetry, which differs from similar dimanganese(II) complexes showing an inversion symmetry for the central Mn(μ-Cl)₂Mn arrangement. Each manganese atom is thereby bound by three nitrogen atoms from a facially coordinated dipa ligand, and three chlorides (1 terminal and 2 μ-bridging) in an octahedrally distorted fashion.The cylovoltammogram of 3 displays that the two manganese(II) ions can independently be oxidized. The magnetic properties of 3 were determined by susceptibility measurements versus temperature. The intramolecular J parameter was determined to a value of J = (−5.2 ± 0.5) cm⁻¹.     

Synthesis, crystal structure and photoelectric property of Mn(II/IV) coordination complexes

Three novel coordination complexes [Mn(tpha)(phen)]_n (1); [Mn(na)₂(H₂O)₂]_n (2); {[Mn(phen)₂(OH)Cl] · Cl · (OH) · (C₉H₁₁NO₂) · 2H₂O} (3) have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction (H₂tpha = terephthalic acid, Hna = nicotinic acid, phen = 1,10-phenanthroline). The tpha groups in complex 1 bridge the Mn(II) ions to an infinite 3D framework. Complex 2 exhibits a 2D network structure in which the Mn(II) ions are linked by nicotinic groups. Complex 3 is connected to a 2D coordination supramolecule by hydrogen bonds. The results of surface photovoltage spectra (SPS) of complexes 1-3 indicate that they all exhibit positive surface photovoltage (SPV) responses in the range of 300-800 nm. However, the intensity, position and numbers of SPV responses are obviously different. The distinctions can be mainly attributed to their structures, valences and coordination environments of the manganese ions in the three complexes. Moreover the external field induced surface photovoltage spectra (FISPS) of the three complexes have been measured.     

Crystal structure of six and seven coordinate manganese(II) complexes with penta and hexadentate pyridylmethyl ligands

Two six-coordinated manganese(II) complexes [Mn(pydien)Cl](ClO₄) · C₂H₅OH (1), [Mn(pydien)NCS](ClO₄) (2) and two seven-coordinated manganese(II) complexes [Mn(pydado)Cl](ClO₄) (3), [Mn(pydado)NCS](ClO₄) (4) have been obtained using linear penta and hexadentate ligands pydien and pydado (pydien: 1,7-bis(2-pyridylmethyl)-1,4,7-triazaheptane and pydado: 1,10-bis(pyridylmethyl)-1,10-diaza-4,7-dioxadecane). The crystal structures for all compounds have been determined. 1 and 3 crystallize in the triclinic space group , 2 crystallizes in the orthorhombic space group Pbca, whereas 4 crystallizes in the monoclinic space group P2₁/c. The bound anion (chloro or isothiocyanato) in complexes 1 and 2 has no influence on the geometry of six-coordinate manganese(II) complexes, whereas the geometry and the wrapping of the hexadentate ligand (pydado) around Mn²⁺ cation depend on the nature of the bound anion. The complex 3 has a capped octahedron geometry with the two pyridyl groups in trans position, while the geometry of complex 4 can be described as pentagonal bipyramid with one pyridyl group and a thiocyanate anion in the axial positions.     

Trinuclear-based coordination compounds of Mn(II) and Co(II) with 4-amino-3,5-dimethyl-1,2,4-triazole and azide and thiocyanate anions: Synthesis, structure and magnetic properties

A 2D layer complex 1 and a linear trinuclear complex 2 with mixed ligands have been synthesized and characterized by elemental analyses, IR and single-crystal X-ray diffraction. In 1, the Mn(II) ions are six-coordinated and lie in distorted octahedron coordination environments. Complex 1 is connected into a 2D layer structure based on a linear trinuclear Mn₃(admtrz)₄(N₃)₆ (admtrz = 4-amino-3,5-dimethyl-1,2,4-triazole) building unit with either (6,3) topology when Mn1 cations as three-connected nodes or (4,4) network when the coordination trinuclear units being regarded as four connected nodes. In 2, the Co(II) ions are in slightly distorted octahedron coordination geometries. The magnetic behaviors are investigated in the temperature range 1.8-300 K. The magnetic susceptibility measurements show that the Mn(II) ions of complex 1 are weakly antiferromagnetically coupled with g = 1.98(1), J1 = −6.31(5) cm⁻¹ and J2 = −1.88(1) cm⁻¹. There is dominant zero field splitting (ZFS) effects with g values, g_// = 2.38(2) and g_⊥ = 4.96(4), indicated a significant presence of the spin-orbit coupling and magnetization experiment reveals large, uniaxial zero-field splitting parameters of D = −29.55 cm⁻¹ for 2.     

EPR and magnetic properties of [Mn(μ-Cl)2(bpy)]n: An unusual ferromagnetic interaction in a Mn(II) chloro-bridged polymer

The study of the magnetic properties and EPR spectra of the one-dimensional bis(μ-chloro) Mn(II) polymer [Mn(μ-Cl)₂(bpy)]_n (1) (bpy = 2,2′-bipyridine) is reported. Magnetic susceptibility measurements reveal a weak ferromagnetic interaction between the Mn(II) ions (J = +0.19 cm⁻¹). This is the first polymer of six-coordinated Mn(II) ions with a [Mn₂(μ-Cl)₂]²⁺ magnetic repeating unit, showing a ferromagnetic interaction. The coordination octahedra are elongated in the Cl?Cl direction and the elongation axes are parallel along the chain. Extended Hückel calculations show that the octahedra share an equatorial-apical edge, with the equatorial plane being parallel, and perpendicular to the Mn₂(μ-Cl)₂. Due to this disposition, the overlap through the chloride bridges is small, so the antiferromagnetic contribution must also be small and, therefore, a ferromagnetic behaviour is observed. The EPR spectra of a polycrystalline sample of 1 at different temperatures are also reported. A variation of the bandwidth with temperature is observed, which could be because this ferromagnetic interaction is weak: above 150 K the dipolar interaction is the predominant effect, while below 150 K the magnetic exchange interaction dominates.     

A new Cu-Mn heterobinuclear complex exhibiting magnetization relaxation

A new heterometallic complex [CuMn(5-Brsap)₂(MeOH)(Ac)] ⋅ CH₃OH (1) (5-Brsap = 5-bromo-2-salicylideneamino-1-propanol) has been synthesized and characterized structurally as well as magnetically. Complex 1 has an alkoxo-bridged Cu(II) and Mn(III) heterobinuclear core, where the Mn(III) and Cu(II) ions have elongated octahedral and square-pyramidal geometries, respectively. In dc magnetic susceptibility measurements reveal that there is strong ferromagnetic interaction between the Mn(III) and Cu(II) ions with an exchange coupling constant J = 67.64 cm⁻¹. The ac magnetic susceptibility measurements, frequency dependence in both the real and imaginary signals is observed, which indicates slow relaxation of magnetization. An Arrhenius plot gave the effective anisotropy barrier Δ/k_B = 11.58 K and the pre-exponential factor ι₀ = 1.28 × 10⁻⁶ s.     

Structure and characterization of a μ-phenoxo-bis μ-acetato dinuclear Mn(II,II) complex [Mn2(LO)(μ-OAc)2](ClO4) (LOH = 2,6-bis{bis(2-(2-pyridyl)ethyl)aminomethyl}-4-methylphenol): Substituent effects

The synthesis, structure and characterization of the dinuclear Mn(II) complex [Mn₂(LO)(μ-OAc)₂](ClO₄) (1) where LOH = 2,6-bis{bis(2-(2-pyridyl)ethyl)aminomethyl)}-4-methylphenol are reported. The reaction of Mn(ClO₄)₂ · 6H₂O with the dinucleating ligand LOH and H₃CCOONa in the presence of NEt₃ in dry, degassed methanol and under an argon atmosphere, yields 1 as a colorless powder. The crystal structure of 1, determined by X-ray diffraction methods, shows a dinuclear Mn(II) complex in which two Mn(II) ions, each in six-coordinate approximate octahedral coordination, are bridged by the phenolate oxygen of LO⁻ and by two acetate ions in a syn,syn-1,3-bridging mode. The Mn-Mn distance is 3.557(1) Å and Mn-O_phenolate-Mn angle is 112.50(9)°. Cyclic voltammetry of 1 in acetonitrile solution shows a quasi-reversible wave at E_1/2 = 0.65 V, for the Mn₂(II,II)/Mn₂(II,III) redox process, and an irreversible oxidation peak at E_p,c = 1.22 V versus Ag/AgCl for the Mn₂(II,III) to Mn₂(III,III) oxidation process. Controlled potential electrolysis of 1 in acetonitrile solution at 0.85 V (versus Ag/AgCl) takes up 1 F of charge per mole of 1 to yield a brown solution of the Mn₂(II,III) state of the complex, which, however, is unstable and reverts back to the Mn₂(II,II) state in solution at room temperature. Least square fitting of the variable temperature magnetic susceptibility measurements on powdered sample of 1 is obtained with g = 1.888, J = −2.75 cm⁻¹, Par = 0.008, TIP = 0. The low −J value and the room temperature calculated magnetic moment of the complex (5.30 BM per Mn(II)), which is less than the spin-only moment of Mn(II), show that the two Mn(II) ions are weakly antiferromagnetically coupled.     

Synthesis, crystal structure and magnetic characterization of a series of four phenoxo-bridged binuclear manganese(III) Schiff base complexes

A family of four new phenoxo-bridged binuclear manganese(III) complexes of the general formula, [Mn(L)(X)]₂ where L = [N,N′-bis(salicylidene)]propane-1,2-diamine and X = salicylaldehyde anion (sal⁻) (1); NCS⁻ (2); NCO⁻ (3) and [Mn(L′)(N₃)]₂·2C₂H₅OH (4) where L′ = [N,N′-bis(2-hydroxyacetophenylidene)]propane-1,2-diamine has been prepared. The syntheses have been achieved by reacting manganese perchlorate with 1,2-diaminopropane and salicylaldehyde (or 2-hydroxyacetophenone for 4) or along with the respective pseudohalides so that the tetradentate Schiff base H₂L or H₂L′ is obtained in situ to bind the Mn(III) ion. The complexes have been characterized by IR spectroscopy, elemental analysis, crystal structure analysis and variable-temperature magnetic susceptibility measurements. The single crystal X-ray diffraction studies show that the compounds are isostructural containing dimeric Mn(III) units with bridging phenolate oxygen atoms. Low temperature magnetic studies indicate that the complexes 1-3 exhibit intradimer ferromagnetic exchange as well as single-molecule magnet (SMM) behavior while complex 4 is found to undergo an intradimer antiferromagnetic coupling.     

Synthesis, structures and magnetic properties of oxamido-bridged trinuclear Cu-M-Cu macrocyclic complexes (M = Mn(II) and Co(II))

Two oxamido-bridged trinuclear complexes of formula {[(LCu)(EtOH)]₂Mn(EtOH)₂}(ClO₄)₂ (1) and {[(LCu)(EtOH)]₂Co(EtOH)₂}(ClO₄)₂ · 2H₂O (2) (H₂L = 2,3-dioxo-5,6:13,14-dichlorobenzo-7,12-diphenyl-1,4,8,11-tetraazacyclo-pentadeca-7,11-diene) have been synthesized and structurally characterized. The central ions of complexes 1-2 (Mn(II), Co(II)) are all bridged by macrocyclic oxamido groups. Their magnetic properties were studied by susceptibility versus temperature measurement, the best fitting of the experimental data led to J = −16.91 cm⁻¹ for 1 and J = −27.73 cm⁻¹ for 2.     

Structural variability in manganese(II) complexes of N,N′-bis(2-pyridinylmethylene) ethane (and propane) diamine ligands

Manganese(II) complexes, Mn₂L¹₃(ClO₄)₄, MnL¹(H₂O)₂(ClO₄)₂, MnL²(H₂O)₂(ClO₄)₂, and {(μ-Cl)MnL²(PF₆)}₂ based on N,N′-bis(2-pyridinylmethylene) ethanediamine (L¹) and N,N′-bis(2-pyridinylmethylene) propanediamine (L²) ligands have been prepared and characterized. The single crystal X-ray diffraction analysis of Mn₂L²₃(ClO₄)₄ shows that each of the two Mn(II) ion centers with a Mn-Mn distance of 7.15 Å are coordinated by one ligand while a common third ligand bridges the metal centers. Solid-state magnetic susceptibility measurements as well as DFT calculations confirm that each of the manganese centers is high-spin S = 5/2. The electronic structure obtained shows no orbital overlap between the Mn(II) centers indicating that the observed weak antiferromagentism is a result of through space interactions between the two Mn(II) centers. Under different reaction conditions, L¹ and Mn(II) yielded a one-dimensional polymer, MnL¹(H₂O)₂(ClO₄)₂. Ligand L² when reacted with manganese(II) perchlorate gives contrarily to L¹ mononuclear MnL²(H₂O)₂(ClO₄)₂ complex. The analysis of the structural properties of the MnL²(H₂O)₂(ClO₄)₂ lead to the design of dinuclear complex {(μ-Cl)MnL²(PF₆)} where two chlorine atoms were utilized as bridging moieties. This complex has a rhomboidal Mn₂Cl₂ core with a Mn-Mn distance of 3.726 Å. At room temperature {(μ-Cl)MnL²(PF₆)} is ferromagnetic with observed μ_eff = 4.04 μ_B per Mn(II) ion. With cooling, μ_eff grows reaching 4.81 μ_B per Mn(II) ion at 8 K, and then undergoes ferromagnetic-to-antiferromagnetic phase transition.     

Syntheses, crystal structures and magnetic properties of 1D and 2D cobaltous coordination polymers with mixed ligands

Two new Co(II) coordination polymers with mixed ligands, {[Co(BTA)_0.5(DBI)₂]·DBI·H₂O}_n (1) and [Co(PDA)(DBI)(H₂O)]_n (2) (H₄BTA = benzene-1,2,4,5-tetracarboxylic acid; H₂PDA = 2,2′-(1,2-phenylene)diacetic acid; DBI = 5,6-dimethyl-1H-benzoimidazole) have been synthesized under hydrothermal conditions, respectively. Both of them are characterized by elemental analyses, powder X-ray diffraction, thermogravimetric analysis, single-crystal X-ray diffraction, and magnetic susceptibilities. In 1, the Co(II) ions are four-coordinated and lie in distorted tetrahedron coordination environment. 1D ladder-like chain structure is formed by the bridging BTA⁴⁻ ligand. In 2, the Co(II) ions are in slightly distorted octahedral coordination geometry, and linked by PDA²⁻ ligand exhibiting a 2D layer structure. Temperature-dependent magnetic susceptibility measurements of 1 and 2 revealed that there are antiferromagnetic interactions between Co(II) ions.     

Formation of coordination polymer and molecular complex of 4,4′-bipyridyl-N,N′-dioxide of manganese and zinc

A 1D-coordination polymer [{Mn₃(C₆H₅COO)₆(BPNO)₂(MeOH)₂}(MeOH)₂]_n (1) having benzoate as the anionic ligand and 4,4′-bipyridyl-N,N′-dioxide (BPNO) as bridging ligand is synthesized by reacting benzoic acid with manganese(II) acetate tetrahydrate followed by reaction with 4,4′-bipyridyl-N N′-dioxide. The bridging bidentate BPNO ligands in this coordination polymer along with the benzoate bridges hold the repeated units. The chain like structure in one dimension by benzoate bridges are connected to each other through the μ³-η²:η¹ bridges of BPNO ligands. This coordination polymer can be transformed to a molecular complex [Mn(H₂O)₆](C₆H₅COO)_2.4BPNO (2). In this complex the BPNO remains outside the coordination sphere but they are hydrogen bonded to water molecules to form self assembled structure. The reaction of 3,5-pyrazoledicarboxylic acid (L₁H2) and BPNO with manganese(II) acetate or zinc(II) acetate led to molecular complexes with composition [M₂(L₁)₂(H₂O)₆].BPNO·xH₂O {where M = Mn(II) (3), Zn(II)(4)}. These molecular complexes of BPNO are characterised by X-ray crystallography. The complexes 3-4 are binuclear carboxylate complexes having M₂O₂ core formed from carboxylate ligands with two metal ions.     

New pyridine-monoacylhydrazidate-coordinated transition-metal complexes

By applying the hydrothermal in situ acylation reactions between alkyl-substituted pyridine-2,3-dicarboxylic acids and hydrazine hydrate, six pyridine-monoacylhydrazidate-coordinated transition-metal complexes [Mn(MPDH)₂] 1, [M(MPDH)₂(H₂O)₂]·2H₂O (M²⁺ = Co²⁺2, Zn²⁺3), [Mn(EPDH)₂(H₂O)₂] 4 and [M(EPDH)₂(H₂O)₂] (M²⁺ = Zn²⁺5, Co²⁺6) (MPDH = 6-methylpyridine-2,3-dicarboxylhydrazidate; EPDH = 5-ethylpyridine-2,3-dicarboxylhydrazidate) were obtained. Although only compound 1 is a 1-D chained coordination polymer and the others are the mononuclear molecular entities, they all further self-assemble into the interesting supramolecular networks via hydrogen-bonded interactions between pyridine-monoacylhydrazidate ligands. Two Zn²⁺ compounds 3 and 5 possess the fluorescence properties with maximum emissions at 517 nm for 3 and 530 nm for 5 upon excitation, respectively. The magnetic analysis for compound 1 indicates there exists the antiferromagnetic interactions between the Mn(II) ions.     

A systematic study on the thermal decomposition reactions of coordination polymers based on metal(II) selenocyanates and 4,4′-bipyridine: Directed synthesis of a μ-1,3 bridging selenocyanate

Reaction of manganese(II), iron(II), cobalt(II) and nickel(II) selenocyanate with 4,4′-bipyridine (bipy) in water at room temperature leads to the formation of the ligand-rich 1:2 hydrates [{M(bipy)(NCSe)₂(H₂O)₂}·bipy]_n (bipy = 4,4′-bipyridine) with M = Mn (1-Mn), Fe (1-Fe), Co (1-Co) and Ni (1-Ni). In their crystal structures, the metal cations are coordinated by two terminally N-bonded selenocyanato anions, two water molecules, and two bridging bipy ligands in an octahedral coordination mode. These building blocks are connected into linear M-bipy-M chains, which are further linked by hydrogen bonds between the water molecules and non-coordinated bipy ligands into layers. On heating these precursor compounds, they decompose into ligand-rich 1:2 anhydrates [M(NCSe)₂(bipy)₂]_n with M = Mn (2-Mn), Fe (2-Fe), Co (2-Co) and Ni (2-Ni). After water removal the coordination spheres of the metal cations are completed by N-coordination of the bipy ligand which formerly was involved in OH···N hydrogen bonding. On further heating, the manganese(II) compound loses half of its bipy ligands leading to a new ligand-deficient 1:1 intermediate [Mn(NCSe)₂(bipy)]_n (3-Mn) with μ-1,3-bridging selenocyanato anions. In contrast, all other compounds decompose without the formation of ligand-deficient intermediates. These structural changes are accompanied with a dramatic change in their magnetic properties: Whereas all ligand-rich 1:2 compounds 1-M and 2-M (M = metal) show only Curie-Weiss paramagnetism, in the ligand-deficient 1:1 intermediate 3-Mn an antiferromagnetic long-range ordering at T_N = 10.5 K is found. The thermal and magnetic properties are qualitatively compared with those of the related ligand-rich and ligand-deficient selenocyanato and thiocyanato compounds based on bipy, pyrazine and pyrimidine as ligand.     

Chlorido-bridged polymeric and dinuclear copper(II) complexes with tridentate Schiff base: Synthesis, crystal structure and magnetic properties

Two copper(II) complexes, [Cu(qsal)Cl](DMF) (1) and [Cu₂(qsalBr)₂Cl₂](DMF) (2), with tridentate Schiff base ligands, 8-(salicylideneamino)quinoline (Hqsal) and 8-(5-bromo-salicylideneamino)quinoline (HqsalBr), respectively, were synthesised and structurally characterized. Each copper(II) ion in the two complexes is in a distorted square pyramidal N₂OCl₂ environment. Complex 1 exists as a polymeric species via equatorial-apical chloride bridges, whereas 2 is a di-chlorido-bridged dinuclear complex, where each bridging chloride simultaneously occupies an in-plane coordination site on one copper(II) ion and an apical site on the other copper(II) ion. Variable-temperature magnetical susceptibility measurements on the two complexes in the temperature range 2-300 K indicate the occurrence of intrachain ferromagnetic (J = +6.58 cm⁻¹) and intramolecular antiferromagnetical (J = −6.91 cm⁻¹) interactions.     

Unprecedented formation of binuclear copper(II) complex with a perylene derived ligand by the oxidative reaction

A new perylene-pendent tridentate ligand, N-(3-perylenylmethyl)-N,N-bis(2-pyridylmethyl)amine (perbpa) 1 and its Cu(II) complex, [Cu(perbpa)Cl₂] (2) were prepared and structurally characterized by the X-ray diffraction method. In the packing structure of ligand 1, perylene groups were aggregated to form a π-π stacked layer of dimerized pelylene moieties similar to the packing of pristine perylene. This result suggests both that the π-π interactions among the perylene moieties predominate for the arrangement of perbpa molecules in the crystal and that this ligand is a good candidate for constructing electron conducting path. A complex 2 was prepared from the ligand 1 and a copper(II) chloride dehydrate. Complex 2 had a mononuclear and 5-coordinate distorted square pyramidal structure with a perbpa and two coordinated chloride ions. The chemical oxidation of 2 by iodine resulted in the unprecedented binuclear Cu(II) species, [Cu₂(μ-Cl)₂(perbpa)₂](I₃)₂, 3·(I₃)₂. An X-ray crystal structure analysis of 3·(I₃)₂ revealed the binuclear structure bridged by the chloride ions. A temperature dependent magnetic susceptibility measurement of 3 showed a weak ferromagnetic exchange interaction with S = 1 ground state, g = 2.12 and J = +1.17 cm⁻¹, based on H = −2JS₁ · S₂. The UV-Vis absorption and the EPR spectra of 3 showed that the perylene groups are not oxidized. These results indicate a couple of Cu(II) constructed S = 1 ground state with intermolecular ferromagnetic interaction. The electrochemical study suggested that the crystallization of 3·(I₃)₂ was initiated by the oxidation of the N,N-bis-(2-pyridylmethyl)amino (bpa) groups of 2 by I₂.     

Stabilization of Mn(II) and Mn(III) in mononuclear complexes derived from tridentate ligands with N2O donors: Synthesis, crystal structure, superoxide dismutase activity and DNA interaction studies

A new family of tridentate ligands PhimpH (2-((2-phenyl-2-(pyridin-2-yl)hydazono)methyl)phenol), N-PhimpH (2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)napthalen-1-ol), Me-PhimpH (2-(1-(2-phenyl-2-(pyridine-2-yl)hydrazono)ethyl)phenol) have been synthesized and characterized. The ligands PhimpH and N-PhimpH after deprotonation react with manganese(II) and manganese(III) starting materials affording [Mn(Phimp)₂] (1), [Mn(Phimp)₂](ClO₄) (2), [Mn(N-Phimp)₂] (3), [Mn(N-Phimp)₂](ClO₄) (4). Complexes [Mn(Phimp)₂] (1) and [Mn(N-Phimp)₂] (3) convert to [Mn(Phimp)₂]⁺ (cation of 2) and [Mn(N-Phimp)₂]⁺ (cation of 4) respectively upon oxidation. Ligand Me-PhimpH stabilized only manganese(III) centre resulting [Mn(Me-Phimp)₂](ClO₄) (5). The molecular structures of [Mn(Phimp)₂], 1 and [Mn(Phimp)₂](ClO₄), 2 were determined by single crystal X-ray diffraction. X-ray crystal structures of 1 and 2 have revealed the presence of distorted octahedral MnN₄O₂ coordination sphere having meridionally spanning ligands. Electrochemical studies for the complexes showed Mn(II)/Mn(III), (E_1/2 = 0.14-0.40 V) and Mn(III)/Mn(IV), (E_1/2 = 0.80-1.06 V) couples vs. Ag/AgCl. The redox properties were exploited to examine superoxide dismutase (SOD) activity using Mn(II)/Mn(III) couple. The complexes 1, 2, 4 and 5 have been revealed to catalyze effectively the dismutation of superoxide () in xanthine-xanthine oxidase-nitro blue tetrazolium assay and IC₅₀ values were found to be 0.29, 0.39, 1.12 and 0.76 μM respectively. DNA interaction studies with complex 2 showed binding of DNA in a non-intercalative pathway. Complexes 1, 2 and 4 exhibited nuclease activity in presence of H₂O₂ and inhibition of activity was noted in presence of KI.     

Structure and magnetism of two new linear trinuclear copper(II) clusters obtained from the tetradentate N2O2 ligand bis(2-hydroxybenzyl)-1,3-diaminopropane

Reaction of bis(2-hydroxybenzyl)-1,3-diaminopropane (H₂bhbd) with copper(II) perchlorate and copper(II) chloride in methanol, respectively, leads to linear trinuclear clusters, namely [Cu₃(bhbd)₂(CH₃OH)₂(ClO₄)₂] (1) and [Cu₃(bhbd)₂Cl₂](CH₃OH)₄ (2). These coordination compounds were characterized by X-ray crystallography, UV-Vis, IR and EPR spectroscopy, and magnetic susceptibility measurements. Both complexes have a linear trinuclear array of copper ions bridged by means of phenolato O atoms and separated by a distance of 2.985(4) Å (1) and 2.937(4) Å (2). Strong antiferromagnetic interactions between these adjacent Cu^II ions govern the magnetochemistry of 1 (J = −303(1) cm⁻¹) and 2 (J = −482(3) cm⁻¹) resulting in S = 1/2 ground states fully populated below 150 K. A correlation between the interaction parameter J and the angles within the trinuclear clusters is proposed.