Spectroscopic properties of neodymium(III)-containing polyoxometalates in aqueous solution

The spectroscopic properties of the neodymium(III)-containing polyoxometalates (POMs) [Nd(PW(11)O(39))(2)](11-), [Nd(PMo(2)W(9)O(39))(2)](11-), [Nd(PMo(4)W(7)O(39))(2)](11-), [Nd(PMo(6)W(5)O(39))(2)](11-), [Nd(SiMo(2)W(9)O(39))(2)](13-), [Nd(P(2)W(17)O(61))(2)](17-), [NdW(10)O(36)](9-), [NdP(5)W(30)O(110)](12-) and [NdAs(4)W(40)O(140)](25-) are described. Absorption spectra of aqueous solutions of the complexes have been recorded and the transition intensities are parameterised in terms of the Judd-Ofelt intensity parameters Omega(lambda) (lambda=2, 4, 6). Marked differences were found between the luminescence lifetimes of the complexes of the type Nd(POM) and those of the type Nd(POM)(2), due to a better shielding of the neodymium(III) ions from the bulk water molecules in the latter type of complexes.     

Manganese(III,IV) and manganese(III) oxide clusters trapped by copper(II) complexes

Reactions of quinquedentate Schiff base ligands with Mn and Cu ions afforded icosa- and hexadecanuclear mixed-metal clusters in which dinuclear CuII complexes trapped oxo-bridged [MnIII8MnIV4O12] and [MnIII6O6] cores, respectively. Maximum entropy method analysis for synchrotron X-ray diffraction data was used to determine the oxidation states of the Mn ions.     

Redox chemistry of mononuclear manganese(II), binuclear manganese(III) and binuclear mixed manganese(II)-manganese(III) complexes with 3-aminopyrazine-2-carboxylate in dimethylsulphoxide

Summary Mn^II forms a yellow mononuclear species with the title ligand having a 12 stoichiometry and whose conditional stability constant is 8.9 × 10¹⁰ m ^–2. The c.v. of this complex shows an oxidation at +0.78V versus s.c.e. Controlled-potential electrolysis at +0.80V versus s.c.e. yields a binuclear species of Mn^III with a 12 metal:ligand stoichiometry.The addition of Mn^III(urea)₆(ClO₄)₃ to a solution of the ligand produces a mononuclear complex of Mn^III if the concentration of the metal ion is less than 1 mM. At higher concentrations a binuclear species is obtained. The latter is reduced in two steps, at +0.24 and –0.58 V versus s.c.e. Controlled-potential electrolysis at 0.0 V produces a dark green complex after the transfer of 0.5 equivalents of charge per mole of Mn. This binuclear L₂Mn^II-Mn^IIIL₂ mixed-valence complex can be obtained only by electrolysis of the binuclear L₂Mn^IIIMn^IIIL₂ species. Attempts to prepare the complex chemically were unsuccessful - the binuclear Mn^III species was obtained in every case.Author to whom all correspondence should be directed.     

Manganese(II/II/II) and Manganese(III/II/III) Trinuclear Compounds. Structure and Solid and Solution Behavior

Two mixed-valence Mn(III)Mn(II) complexes and a homo-valence Mn(II) trinuclear manganese complex of stoichiometry Mn(III)Mn(II)Mn(III)(5-Cl-Hsaladhp)(2)(AcO)(4)(MeOH)(2).4CH(3)OH (1a), Mn(III)Mn(II)Mn(III) (Hsaladhp)(2)(AcO)(2)(5-Cl-Sal)(2)(thf)(2) (3a) and Mn(II)Mn(II)Mn(II) (AcO)(6)(pybim)(2) (1b) where H(3)saladhp is a tridentate Schiff base ligand and pybim a neutral bidentate donor ligand, have been structurally characterized by using X-ray crystallography. The structurally characterized mixed-valence complexes have strictly 180 degrees Mn(III)-Mn(II)-Mn(III) angles as required by crystallographic inversion symmetry. The complexes are valence trapped with two terminal Mn(III) ions showing Jahn-Teller distortion along the acetate or salicylate-Mn(III)-X axis. The Mn.Mn separation is 3.511 ? and 3.507 ? respectively. The mixed-valence complexes have S = (3)/(2) ground state and the homovalence complex S = (5)/(2), with small antiferromagnetic exchange J couplings, -5.6 and -1.8 cm(-1), respectively, while the powder ESR spectra at 4 K show a broad low field signal with g approximately 4.3 for Mn(III)Mn(II)Mn(III) and a broad temperature-dependent signal at g = 2 for Mn(II)Mn(II)Mn(II). Crystal data for 1a: [C(36)H(60)O(20)N(2)Cl(2)Mn(3)], triclinic, space group P&onemacr;, a = 9.272(7) ?, b = 11.046(8) ?, c = 12.635(9) ?, alpha = 76.78(2) degrees, beta = 81.84(2) degrees, gamma = 85.90(2) degrees, Z = 1. Crystal data for 3a: [C(48)H(56)O(18)N(2)Cl(2)Mn(3)], monoclinic, space group P2(1)/n, a = 8.776(3) ?, b = 22.182(7) ?, c = 13.575(4) ?, beta = 94.44(1) degrees, Z = 2. Crystal data for 1b: [C(36)H(36)O(12)N(6)Mn(3)], triclinic, space group P&onemacr;, a = 13.345(6) ?, b = 8.514(4) ?, c = 9.494(4) ?, alpha = 75.48(1) degrees, beta = 75.83(1) degrees, gamma = 76.42(1) degrees, Z = 1.     

Redox chemistry of 1,2-dihydroxynaphthalene, 1,2-naphthosemiquinone and 1,2-naphthoquinone and their complexes with manganese(II) and manganese(III)

Cyclic voltammetry and controlled-potential electrolyses were carried out on solutions of 1,2-naphthoquinone (1,2-NQ), 1,2-dihydroxynaphthalene [1,2-Di(OH)-Cat] and their reduction and oxidation products in dimethyl sulfoxide. A study of the interaction of these species with MnII and MnIII has been undertaken. The complexes MnIII(Cat2–)33–, MnII(Cat2–)22– and MnII-(Cat2–), where Cat2– represents the dianion of 1,2-dihydroxynaphthalene, were obtained in solution and the species MnIISQ has been detected only on the surface of the electrode. An attempt to obtain the latter complex quantitatively caused intramolecular charge-transfer yielding the more stable MnIII-catechol complex. The MnIII–semiquinone complex is unstable and the ligand is easily oxidized. The charge-transfer reaction between MnIII(Cat2–)33– and MnII(Cat2–)22– is observed at –0.54/–0.52 V versus s.c.e. whereas the MnII complexes are reduced beyond the electrochemical window (at a potential more negative than –2.00 V versus s.c.e). On the other hand, all these species are destroyed when the coordinated ligand is oxidized. U.v.-vis. spectroscopy and magnetic susceptibility measurements were performed on the compounds in solution in order to characterize and to confirm the oxidation states of the metal ion in the species.     

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.     

Synthesis of Iron(II,III)-containing Derivatives of Arabinogalactan

A synthesis of iron(II, III) derivatives of arabinogalactan, involving formation in an alkaline solution of a hydrated iron(II, III) oxide biopolymer, is proposed. Optimal conditions of the synthesis are determined.     

Synthesis of bis(diethyldithiocarbamato)manganese(II) and tris(diethyldithiocarbamato)manganese(III)

An ideal undergraduate introduction to the challenges of synthesis and characterization of air-sensitive compounds is accomplished in the preparation of bis(diethyldithiocarbamato)manganese(II). This economical experiment employs a glovebag, low-cost and low-toxicity chemicals, and is completed in one undergraduate laboratory period. For comparison purposes, the synthesis and characterization of air-stable tris(diethyldithiocarbamato)manganese(III) is also described.     

Synthesis and characterization of phase-pure manganese(II) and manganese(III) silicalite-2

Manganese silicalite-2 was synthesized at high pH using the molecular cluster Mn 12O 12(O 2CCH 3) 16 as a Mn source. The silicalite-2 (ZSM-11) materials were synthesized using 3,5-dimethyl- N, N-diethylpiperdinium hydroxide as a structure-directing agent to produce phase-pure ZSM-11 materials. No precipitation of manganese hydroxide was observed, and synthesis resulted in the incorporation of up to 2.5 mol % Mn into the silicalite-2 with direct substitution into the framework verified by the linear relationship between the unit cell volume and loading. The Mn is reduced to Mn (II) during hydrothermal synthesis and incorporated into the silicalite-2 framework during calcination at 500 degrees C. Further calcination at 750 degrees C does not affect the crystallinity but oxidizes essentially all of the Mn (II) to Mn (III) in the framework. The large difference in oxidation temperatures between the II and III oxidation states provides a means of producing relatively pure manganese(II) and manganese(III) silicalite-2 materials for applications such as catalysis.     

Manganese(II)-containing MRI contrast agent employing a neutral and non-macrocyclic ligand

The ligand N,N'-bis(2-pyridylmethyl)-bis(ethylacetate)-1,2-ethanediamine (debpn) coordinates divalent transition metal ions in either a pentadentate or hexadentate fashion. The coordination number correlates with the ionic radius of the metal ion, with larger cations being heptacoordinate as assessed by solid-state analysis. With Mn(II), the debpn ligand is hexadentate and remains bound to the oxophilic metal ion, even when dissolved in water. The ligand's incomplete coordination of the manganous ion allows water molecules to coordinate to the metal center. These two properties, coupled with the high paramagnetism associated with the S = 5/2 metal center, enable [Mn(debpn)(H(2)O)](ClO(4))(2) to serve as a stable and effective magnetic resonance imaging contrast agent despite the ligand's lack of both a macrocyclic component and an anionic charge.     

Enantiopure sandwich-type nonanuclear Ln(III)3Mn(III)6 clusters

Three enantiopure isostructural sandwich-type clusters, Ln(III)(3)Mn(III)(6) (Ln = Dy (1), Tb (2) and Gd (3)) have been synthesized through reactions of a chiral Schiff-base ligand ((S,E)-4-(2-hydroxybenzylideneamino)-2-hydroxybutanoic acid, H(3)L) with manganese and lanthanide ions, showing intramolecular antiferromagnetic interaction.     

Spectro-thermal characterization of chromium(III) and manganese(II) complexes with carboxyamide

Complexes of Cr(III) and Mn(II) with N′,N″-bis(3-carboxy-1-oxopropanyl) 2-amino-N-arylbenzamidine (H₂L¹) and N′,N″-bis(3-carboxy-1-oxophenelenyl) 2-amino-N-arylbenzamidine (H₂L²) have been synthesized and characterized by various physico-chemical techniques. The vibrational spectral data are in agreement with coordination of amide and carboxylate oxygen of the ligands with the metal ions. The electronic spectra indicate octahedral geometry around the metal ions, supported by magnetic susceptibility measurements. The thermal behavior of chromium(III) complexes shows that uncoordinated nitrate is removed in the first step, followed by two water molecules and then decomposition of the ligand; manganese(II) complexes show two waters removed in the first step, followed by removal of the ligand in subsequent steps. Kinetic and thermodynamic parameters were computed from the thermal data using Coats and Redfern method, which confirm first order kinetics. The thermal stability of metal complexes has been compared. X-ray powder diffraction determines the cell parameters of the complexes.     

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.     

Simultaneous determination of soluble manganese(III), manganese(II) and total manganese in natural (pore)waters

A new spectrophotometric protocol was developed for the simultaneous determination of soluble Mn(III), Mn(II) and total Mn [sum of soluble Mn(III) and Mn(II)] in sediment porewaters using a water soluble meso-substituted porphyrin [α,β,γ,δ-tetrakis(4-carboxyphenyl)porphine (T(4-CP)P)]. A simple kinetic rate model is used to quantify soluble Mn(II), Mn(III) and total Mn concentrations during a metal substitution reaction. Under optimized conditions, the method accurately determines soluble Mn(II) and Mn(III) within a concentration range of 100 nM-10 μM. The detection limit of total soluble Mn is 50 nM. Using this method, soluble Mn(II) and Mn(III) concentrations were determined in standard solutions within 0.4-2% of the known values and agreed closely with results of inductively coupled plasma mass spectrometric and voltammetric analyses. The procedure was successfully applied to determine soluble Mn(II), Mn(III) and total Mn in sediment porewaters of the Lower St. Lawrence Estuary. Mn(III) represented up to 85% of the total soluble Mn pool in surface sediments.     

Investigations of chromium(III), manganese(III), tin(II) and lead(II) dithiocarbamate complexes

Piperidine-, morpholine-4-, N-methylpiperazine-4- and thiornorpholine-4-carbodithioate complexes of chromium(III), manganese(III), tin(II) and lead(II) are prepared and characterized by chemical analyses, spectroscopic methods (I.R. and electronic spectra), magnetic susceptibilities, conductivity measurements and mass spectra. The complexes are of the type M(R₂dtc)n, where n is the oxidation number of the metal ion. Where possible a tentative stereochemistry of the complexes is discussed on the basis of the results obtained. In all the complexes the dithiocarbamate ligands show bidentate behaviour.     

Novel complexes of 5-(4-carboxyl)phenylene-methanaminophenyl-10,15,20-tri-phenylporphyrin with zinc(II), iron(III), manganese(III) and zinc(II)–iron(III), zinc(II)–manganese(III) supramolecular self-assembly by hydrogen bonding

5-(p-Carboxyl)phenylene-methanaminophenyl-10,15,20-triphenylporphyrin (p-CPTPP) and its Zn^II[Zn(p-CPTPP)], Fe^III[Fe^III(p-CPTPP)Cl], Mn^III[Mn^III(p-CPTPP)Cl] complexes were prepared and characterized by elemental analysis, ¹H-n.m.r., i.r. and u.v.–vis. spectroscopy. The behaviour of the supramolecular self-assemblies, Zn(p-CPTPP)–Fe^III(p-CPTPP)Cl and Zn(p-CPTPP)–Mn^III(p-CPTPP)Cl, were studied by steady-state fluorescence spectroscopic titration and u.v.–vis. spectra. The formation constants were determined from the data of fluorescence spectroscopic titration. The fact that the Zn(p-CPTPP)–Mn^III(p-CPTPP)Cl system has a higher formation constant than the Zn(p-CPTPP)–Fe^III(p-CPTPP)Cl system is discussed.     

Coordination Compounds of Chromium(III), Manganese(II), and Iron(III) with Diphenyl Thiocarbazide

Complexes of chromium(III), manganese(II), iron(III) with diphenyl thiocarbazide weresynthesized.     

Oxovanadium(IV), manganese(II) and manganese(III) carbodithioates exhibiting abnormal magnetic behaviour

Summary New carbodithioate complexes of the oxovanadium(IV), manganese(II) and manganese(III) ions have been prepared and studied by i.r. and electronic spectral and variable temperature magnetic susceptibility (77K to room temperature) measurements. The carbodithioate ligands, 4-methylpiperazine-1-carbodithioate (4-MPipzcdt) and 4-phenylpiperazine-1-carbodithioate (4-PPipzcdt), were derived from heterocyclic secondary amines. The VO(4-MPipzcdt)₂ and VO(4-PPipzcdt)₂ complexes possess C _4v symmetry; Mn(4-PPipzcdt)₂ is tetrahedral and Mn(4-PPipzcdt)₃ is octahedral. All exhibit abnormal room temperature magnetic moments and the variable temperature magnetic moments suggest antiferromagnetism for the oxovanadium(IV) and the manganese(II) complexes and the occurrence of low spin (³ T _1g ) high spin (⁵ E _g ) equilibrium in addition to antiferromagnetic interactions in the manganese(III) complex. The spin-spin exchange parameter (-2J) value for the VO(4-MPipzcdt)₂ complex has been calculated using variable temperature magnetic susceptibility data.     

New 3-D La(III)-Cu(II)-containing coordination polymer with a high potential porosity

A new 3-D coordination polymer containing both 3d and 4f ions has been designed. Its chemical formula is La2[Cu(pba)]3(H2O)8 . 8H2O. It crystallizes in the quadratic system, space group I41/a with a = 42.4947(9) Angstrom, c = 16.3378(3) Angstrom, and Z = 16. Its crystal structure can be described as a 3-D molecular framework exhibiting a complex network of interconnected zigzaglike channels. Once crystallization water molecules are removed, this compound presents a high potential porosity and a low density. The porosity has been evaluated using Connolly's algorithm.