Jesús Sanmartín

Mono- and polynuclear complexes of Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with N,N′-bis(3-hydroxysalicylidene)-1,3-diamino-2-propanol

Abstract Mono- and polynuclear neutral complexes have been obtained by direct electrochemical reaction of metal anodes with the potentially heptadentate and tetracompartmental ligand N , N ′-bis(3-hydroxysalicylidene)-1,3-diamino-2-propanol (H 5 L). Physicochemical data suggest that the ligand behaves as a di- or tetra-anion in mono- and polynuclear complexes, respectively. Metal ions are held together by μ-phenoxo oxygen bridges in polynuclear complexes. Nickel and copper environments are distorted to tetrahedral and square-planar, respectively. Zinc and cadmium could be hexa-coordinated in the mononuclear complexes. Finally, iron and cobalt ions seem to be in pseudo-octahedral fields.

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.

General synthesis of ‘salicylaldehyde half-unit complexes’: structural determination and use as synthon for the synthesis of dimetallic or trimetallic complexes and of ‘self-assembling ligand complexes’

Abstract Template synthesis of the ligand resulting from the monocondensation of 1,2-diaminoethane with salicylaldehyde was realized successfully in the presence of copper(II) ions and nitrogen bases (imidazole, pyridine). This ‘half-unit’ ligand, named 4-(2-hydroxyphenyl)-3-aza-3-buten-1-amino or N-(2-aminoethyl)salicylaldimine, is abbreviated as SEH or SE in its deprotonated form. This reaction can be extended to other diamines. The complex [SECuImH]ClO4 crystallizes in the monoclinic space group P21/c (no. 14) with 4 formula weights in the cell having dimensions a = 9.020(1), b = 21.293(2), c = 8.384(1) A , and β = 107.64(1)°. It presents several synthetic applications. Particular attention was paid to the dinuclear imidazole-bridged complexes, with imidazole bridges being free or included in a tetradentate Schiff base, via study of their magnetic properties. Some examples of self-assembling complexes are also given, alongwith [(SECu)4OH](ClO4)2·H2O for which magnetic results confirm the trinuclear structure.

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.

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.

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.

Metallo-helicates with an N4-Schiff base containing a flexible alkyl spacer

Neutral Mn(II), Fe(II) and Co(II) complexes with an N -tosyl substituted N4-Schiff base containing a tetra-methylene spacer have been prepared. The X-ray crystal structures of ligand H2BTs [N ,N ?-bis(2-tosylaminobenzylidene)-1,4-diaminobutane] and helical Co(BTs)/0.5H2BTs have been solved. The Co(II) ion assumes a distorted tetrahedral coordination geometry, involving the four donor N -atoms of the dianionic ligand. Additionally, secondary interactions between the metal centre and one of the O -atoms of each tosyl group were detected. These groups are differently conformed, so that the ligand behaves as a non-symmetric helicand. # 2002 Elsevier Science B.V. All rights reserved.