Matilde Fondo

Synthesis and structural characterisation of new manganese(II) and (III) complexes. Study of their photolytic and catalase activity and X-ray crystal structure of [Mn(3-OMe, 5-Br-salpn)(EtOH)(H2O)]ClO4

Abstract New [MnIIL(H2O)2] and [MnIIIL(H2O)2]ClO4 complexes, where L are substituted N,N′-bis(salicylidene)propane-1,3-diamine (H2salpn) ligands have been prepared and thoroughly characterised by elemental analysis, IR and mass spectroscopy, conductivity and magnetic measurements at room temperature (and, in the case of 1, at variable temperature). Cyclic and normal pulse voltammetry measurements were also performed. All these studies support an octahedral geometry around the metal with the Schiff base in the equatorial plane acting as tetradentate and solvent molecules in the axial positions. Crystallographic characterisation of 6 confirms this geometry and shows a supramolecular structure involving π–π stacking and hydrogen bonding interactions. The ability to split water by these complexes and their catalase activity has also been studied.

Dinuclear nickel complexes with a Ni2O2 core : a structural and magnetic study

The acetylacetonate complexes [Ni(2)L(1)(acac)(MeOH)] x H(2)O, 1 x H(2)O and [Ni(2)L(3)(acac)(MeOH)] x 1.5H(2)O, 2 x 1.5H(2)O (H(3)L(1) = (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine and H(3)L(3) = (2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) were prepared and fully characterised. Their crystal structures show that they are dinuclear complexes, extended into chains by hydrogen bond interactions. These compounds were used as starting materials for the isolation of the corresponding [Ni(2)HL(x)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x n MeOH and [Ni(2)HL(x)(O(2)CCH(2)CO(2))(H(2)O)]x nH(2)O dicarboxylate complexes (x = 1, 3; n = 1-3). The crystal structures of [Ni(2)HL(1)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x MeOH, 3 x MeOH, [Ni(2)HL(3)(o-O(2)CC(6)H(4)CO(2))(H(2)O)] x 3 MeOH, 4 x 3 MeOH and [Ni(2)HL(1)(O(2)CCH(2)CO(2))(H(2)O)] x 2.5H(2)O x 0.25 MeOH x MeCN, 5 x 2.5H(2)O x 0.25 MeOH x MeCN, were solved. Complexes 3-5 show dinuclear [Ni(2)HL(x)(dicarboxylate)(H(2)O)] units, expanded through hydrogen bonds that involve carboxylate and water ligands, as well as solvate molecules. The variable temperature magnetic susceptibilities of all the complexes show an intramolecular ferromagnetic coupling between the Ni(II) ions, which is attempted to be rationalized by comparison with previous results and in the light of molecular orbital treatment. Magnetisation measurements are in accord with a S = 2 ground state in all cases.

A direct route to obtain manganese(III) complexes with a new class of asymmetrical Schiff base ligands

A new class of asymmetrically substituted Schiff base ligands has been synthesised incorporating hard amido donor atoms. The single crystal X-ray structure of one of these ligands, H3-amsal, has been determined [H3-amsal=3-aza-4-(2-hydroxyphenyl)-N-(2-hydroxyphenyl)but-3-enamide]. The structure reveals the ligand to be suitable for use as an equatorially co-ordinating ligand in octahedral complexes. A new route to obtaining manganese(III) complexes of these ligands, with high yield and purity, has been designed. Complexes of the form MnIII(amsal-R)(H2O)n (n=1–4) have been prepared by the electrochemical oxidation of a manganese anode in an acetonitrile solution of the ligands. The compounds have been characterised by elemental analyses, IR and 1H NMR spectroscopies, FAB mass spectrometry, magnetic measurements, ΛM and cyclic voltammetry.

Zinc and cadmium complexes with an achiral symmetric helicand. Crystal structure of an enantiomerically pure Λ-Zn(II) monohelicate

Zn(II) and Cd(II) complexes with an N-tosyl substituted N4-donor Schiff base, containing a 2-propanol residue as spacer, have been prepared. The X-ray crystal structure of the monohelicate Λ-Zn(OHPTs)·H2O [H2OHPTs: N,N′-bis(2-tosylaminobenzylidene)-1,3-diamino-2-propanol] has been solved. The Zn(II) ion assumes a distorted tetrahedral coordination geometry, involving the four donor N atoms of the bisdeprotonated ligand. Strong (O–H⋯O) hydrogen bonds between neighbouring complex and lattice water molecules lead to intricate intermolecular interactions that seem to drive the crystal packing. This Zn(II) complex shows an intense blue fluorescence in solution (λ = 430 nm, ϕ = 0.14), which is also observed in the solid state (λ = 490 nm). Cd(OHPTs)·4H2O, although at a lower level (ϕ = 0.08), is also luminescent (λ = 430 nm) in acetonitrile solution.

Dinuclear Co(III)/Co(III) and Co(II)/Co(III) mixed-valent complexes: synthetic control of the cobalt oxidation level

The reactivity of cobalt(II) salts towards H(3)L (2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) was studied in different reaction conditions. Accordingly, the interaction of cobalt(II) acetate with H(3)L in methanol gives rise to the discrete complex [Co(III)(2)L(OAc)(2)(OMe)]*1.5H(2)O.MeOH, 1. Reaction of cobalt(II) acetylacetonate with H(3)L in the presence of dicarboxylic acids was also investigated. Thus, when cobalt(II) acetylacetonate and H(3)L are mixed with terephthalic or malonic acid in 4 : 2 : 1 molar ratios, the mixed valent [Co(II/III)(2)L(acac)(p-O(2)CC(6)H(4)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*2H(2)O*2MeOH, 2 and [Co(II/III)(2)L(acac)(O(2)CCH(2)CO(2)H)][Co(II/III)(2)L(acac)(OH)]*7H(2)O, complexes are isolated. Decreasing the pH of the medium, by addition of a second mol of dicarboxylic acid, leads to [Co(II/III)(2)L(O(2)CCH(2)CO(2))(MeOH)]*2MeOH, 4, while the reaction with terephthalic acid does not proceed. 1, 2 and 4 were crystallographically characterised and all the complexes are dinuclear, with hydrogen bonds that expand the initial nodes. The magnetic characterisation, as well as the NMR spectroscopy, indicates a diamagnetic nature for 1, in agreement with the presence of Co(III), showing the aerial oxidation suffered by the cobalt(II) ions. Nevertheless, are paramagnetic. Temperature variable magnetic measurements were recorded for the crystallographically characterised complexes 2 and 4 and these studies confirm the mixed valence Co(II)/Co(III) nature of the compounds. The best fits of the magnetic data give an axial distortion parameter Delta = 628.7 cm(-1) for 2 and 698.8 cm(-1) for 4, and spin-orbit coupling constant lambda = -117.8 cm(-1) for 2 and -107.0 cm(-1) for 4. Therefore, this study shows that the oxidation degree of the initial cobalt(ii) salt by atmospheric oxygen can be controlled according to the pH of the medium.

Control of the Microarchitecture of a Double Helix − Electrochemical Synthesis and Characterisation of a Novel Dinickel(II) Helicate with Different Groove Sizes

Self-assembly of nickel ions and the N4 Schiff base H2PTs [H2PTs: N,N′-bis(2-tosylaminobenzylidene)-1,3-diaminopropane] in an electrochemical cell leads to the novel neutral double-stranded dinuclear helicate [NiPTs]2·CH3CN (1). Complex 1 was fully characterised by elemental analysis, IR and EPR spectroscopy, FAB mass spectrometry, and magnetic measurements. The single X-ray crystal structure of 1 shows that both ligands are asymmetrically positioned around the Ni−Ni axis, leading to a double-helical complex that presents a major and a minor groove.

The diversity observed in manganese(III) complexes of tetradentate Schiff base ligands: An assessment of structural trends

Abstract A series of manganese(III) complexes of aryl substituted N 2 O 2 donor set Schiff base ligands has been prepared by the aerial oxidation of manganese(II) precursors. The resultants complexes of stoichiometry [MnL]C1O 4 · n H 2 O (where n = 1–3) have been thoroughly characterised by elemental analyses, infrared spectroscopy, fast atom bombardment (FAB) mass spectrometry, magnetic susceptibility measurements and paramagnetic 1 H NMR. The crystal structure of [MnL 7 (H 2 O) 2 ]ClO 4 ·H 4 O, 1 , shows it to consist of a polymeric array of roughly octahedtal [MnL 7 (H 2 O) 2 ] + cations linked via an intricate network of hydrogen bonds between the perchlorate counterion and the lattice water molecule. This hydrogen bonding is further enhanced by π-π stabilisation between the aryl rings of the Schiff base ligands. An attempt is made to rationalise the structural chemistry observed by us for complexes of this type.

New Helical Complexes with a Bis(bidentate) Schiff Base Ligand Containing a Flexible Spacer

Neutral complexes with the general empirical formula M(PTs) [M: Mn, Fe, Co, Cu, Zn, and Cd; H2PTs: N,N′-bis(2-tosylaminobenzylidene)-1,3-diaminopropane] were obtained by means of an electrochemical procedure. All complexes were characterised by elemental analyses, mass spectrometry, IR and 1H NMR spectroscopy, and magnetic measurements, where appropriate. Recrystallisation of the cobalt, copper, and zinc complexes yielded single crystals of [Co(PTs)] (1), [Cu(PTs)]·1.5CH3CN (2) and [Zn(PTs)]2·1.5H2O·CH3CN (3). Their X-ray characterisation shows that 1 and 2 are mononuclear tetrahedral single-stranded helical complexes in the solid state, while 3 is a double-helical compound containing a major and a minor groove, with the Schiff base acting as a bis(bidentate) N4 donor.

Structural and photolytic studies on new mononuclear and binuclear manganese complexes containing Schiff base ligands. The crystal structure of [Mn(μ-3,5-Brsalpn)(μ-O)]2·2DMF

Abstract Mononuclear and binuclear manganese Schiff base complexes containing substituted N,N′-bis(salicylidene)propane-1,3-diamine ligands, H2(Rsalpn) (R=5-Br, 3,5-Br and 3,5-Cl), have been prepared and characterised by elemental analyses, IR and EPR spectroscopy, FAB and LDI-TOF mass spectrometry, cyclic voltammetry and magnetic measurements. The structure of [Mn(3,5-Brsalpn)O]2·2DMF (5) has been determined by X-ray diffraction techniques. The compound has a dimeric structure with μ-oxo bridges and the ligand spanning both metal centres. The capacity of the complexes to oxidise phenothiazine and their ability to catalyse the photolysis of water have also been studied.

Insights into the absorption of carbon dioxide by zinc substrates: isolation and reactivity of di- and tetranuclear zinc complexes

The heptadentate Schiff base H(3)L can react with zinc acetate to form the discrete dinuclear complex Zn(2)L(OAc)(H(2)O), 1.H(2)O. The reaction of 1.H(2)O with NMe(4)OH.5H(2)O both in air and under an argon stream has been investigated. On one hand, this reaction in air yields the tetranuclear complex (Zn(2)L)(2)(CO(3))(H(2)O)(6), 2.5H(2)O, by spontaneous absorption of adventitious carbon dioxide. This process can be reverted in an acetic acid medium, whereas the treatment of 2.5H(2)O with methanoic acid yields crystals of [Zn(2)L(HCOO)].0.5MeCN.1.25MeOH.2H(2)O, 3.0.5MeCN.1.25MeOH.2H(2)O. On the other hand, the interaction under an argon atmosphere of 1.H(2)O with NMe(4)OH.5H(2)O in methanol allows the isolation of the dinuclear complex Zn(2)L(OMe)(H(2)O)(4), 4.4H(2)O. Recrystallisations of 1.H(2)O, 2.5H(2)O and 4.4H(2)O, in different solvents, yielded single crystals of 1.MeCN.2.5H(2)O, 2.4MeOH and 4.3MeOH.H(2)O, respectively. The crystal structure of 2.4MeOH can be understood as resulting from an unusual asymmetric tetranuclear self-assembly from two dinuclear units, and shows three different geometries around the four zinc atoms.