Ana M. González-Noya

Conformational rearrangement of 2,6-bis(1-salicyloylhydrazonoethyl)pyridine (H4daps) on complexation. Synthesis and X-ray characterisation of H4daps and its copper helicate complex [Cu(H2daps)(H2O)]2·2CH3CN

The copper complex of 2,6-bis(1-salicyloylhydrazonoethyl)pyridine, H4daps, has been prepared by an electrochemical procedure and characterised by elemental analysis, IR, FAB mass spectroscopy, ΛM, magnetic susceptibility measurements and EPR studies. The molecular structures of the ligand H4daps (1) and its copper complex [Cu(H2daps)(H2O)]2·2CH3CN (3) have been determined by X-ray diffraction studies. The ligand shows in the solid state a syn-open conformation that allows it to act as a binucleating ligand, after a conformational change, as is shown by the study of the copper dihelicate 3. This compound contains the dianionic ligand [H2daps]2− in an anti-open conformation. The comparative study of this complex, with others previously reported, allows us to confirm that the conformational rearrangement undergone by H4daps upon complexation depends strongly on the metal nature and its stereochemical preferences.

A new type of manganese-Schiff base complex, catalysts for the disproportionation of hydrogen peroxide as peroxidase mimics

New manganese(II) and manganese(III) complexes of substituted N,N′-bis(salicylidene)-1,2-diimino-2-methylethane have been prepared and characterized. Elemental analysis, IR and EPR spectroscopies, mass spectrometry, magnetic measurements and the study of their redox properties have confirmed their respective formulae as MnIIL(H2O)2 and MnIIIL(H2O)n(ClO4). Electron-withdrawing substituents on the phenyl rings of the ligand stabilize the oxidation state (II) for manganese, but the electron-donating substituents on the Schiff bases are those that lead to Mn(III) complexes, which behave as efficient peroxidase mimics in the presence of the water-soluble trap ABTS. The rate of peroxidase activity of the present complexes is significantly higher than that of other series of Mn-Schiff base compounds, probably due to their versatility in adopting in solution a structure that allows the coordination of the hydrogen peroxide substrate molecule to the manganese.

Pentadentate thiosemicarbazones as versatile chelating systems. A comparative structural study of their metallic complexes

We have prepared some transition and post-transition metal complexes derived from the pentadentate thiosemicarbazone ligand bis(4-N-ethylthiosemicarbazone)-2,6-diacetylpyridine H(2)L(Et), by both chemical and electrochemical procedures. The complexes have been synthesised and fully characterised, including the crystal structures for the ligand H(2)L(Et) and its manganese, cadmium and lead complexes. We have also performed multinuclear (109)Ag, (113)Cd, (119)Sn and (207)Pb studies for silver, cadmium, tin and lead compounds, respectively. Moreover we present here a comparative study on the different structures found for pentadentate thiosemicarbazonate complexes, trying to check the influence of different factors, such as experimental procedure, size of metal, structure of the ligand, and metal oxidation state, on the final structure of the complex formed. Our aim is gaining a better insight into the coordination trends of pentadentate thiosemicarbazone ligands.

Influence of the metal size in the structure of the complexes derived from a pentadentate [N3O2] hydrazone

The influence of the metal size in the nuclearity of the complexes derived from the hydrazone ligand 2,6-bis(1-salicyloylhydrazonoethyl)pyridine [H(4)daps] has been investigated. We have synthesised a series of new complexes [M(H(x)daps)] x yH(2)O, (x = 2,3; y = 0-3) with M = Ag (1), Cd (2), Al (3), Sn (4) and Pb (6), using an electrochemical procedure. The crystal and molecular structures have been determined for the mononuclear complexes [Sn(H(2)daps)(H(2)O)(2)] x 4H(2)O (5) and [Pb(H(2)daps)(CN)][Et(4)N] (7). Complex is the first neutral Sn(II) complex derived from a pentadentate hydrazone Schiff base ligand. Complex shows the lead coordinated to the hydrazone donor set and a cyanide ligand, being the first reported complex with the lead atom coordinated to a monodentate cyanide group. Additionally, we have synthesised the lead complex using chemical conditions, in the presence of sodium cyanide which allowed us to isolate the neutral complex [Pb(H(2)daps)] (8). Evaporation of these mother liquors led the novel compound [Pb(Hdaphs)(CH(3)COO)] (9). Complex 9 shows the initial ligand hydrolysed in one of the imine bonds giving rise to a new tetradentate ligand [H(2)daphs] coordinated to the lead atom and a bidentate acetate group. Moreover, the solution behaviour of the complexes has been investigated by (1)H, (113)Cd, (117)Sn and (207)Pb NMR techniques. In particular multinuclear NMR has provided new useful data to correlate factors such as oxidation state, coordination number and nature of the kernel donor atoms due to the new coordination found in complexes 5 and 7. The comparative study of the structures of the complexes derived from this pentadentate [N(3)O(2)] hydrazone ligand let us to conclude that the metal size is a key factor to control the nuclearity of the complexes derived from the ligand [H(4)daps].

Coordinative trends of a tridentate thiosemicarbazone ligand: synthesis, characterization, luminescence studies and desulfurization processes

The coordinative chemistry of the tridentate thiosemicarbazone ligand 2-pyridinecarboxaldehyde 4-N-ethylthiosemicarbazone (HL(Et)) has been explored by using an electrochemical methodology. All the complexes have been characterized using analytical and spectroscopic techniques. In the case of copper we have isolated two different complexes, with Cu(L(Et))(2).4H(2)O (6) and [Cu(2)(L(Et))(2)(SO(4))] (7) formulae. The sulfate group coordinated to the copper atoms in was probably released to the media as a consequence of a desulfurization process. Single X-ray crystallography has been carried out for the ligand HL(Et) and the complexes , [Ag(6)(L(Et))(6)].CH(3)CN (9) and [Pb(L(Et))(2)] (2). The copper(ii) complex is a dimer compound in which two antiparallel monodeprotonated ligands are coordinated to two copper centres by establishment of mu(2)-thiolate bridges and the additional coordination of a sulfate group bridging the two metal atoms. The silver complex is an unusual hexanuclear cluster compound with a wheel-type conformation, while the lead complex is a monomer which exhibits the lone pair effect. A structural comparative study of the electrochemically obtained complexes derived from HL(X) ligands (X= Me, Et and Ph) have been performed. Finally, the solution behaviour of the complexes was checked by NMR, UV and fluorescence studies.

The coordination preferences of metal centres modulate superexchange coupling interactions in a metallo-supramolecular helical assembly

A method to modulate the strength of the superexchange coupling interaction in dinuclear helical assemblies based on the coordination preferences of the metal centres is described.

Alkali-metal-ion-directed self-assembly of redox-active manganese(III) supramolecular boxes.

The ability to organize functional molecules into higher dimensional arrays with well-defined spatial relationships between the components is one of the major goals in supramolecular chemistry. We report here a new route for the preparation of supramolecular boxes, incorporating two types of metal ions: (i) alkali-metal ions, which induce the supramolecular architecture and essentially play a structural role in the final compounds; (ii) manganese(III) ions, which are redox-active systems and give functionality to the new cages. Our results evidence that the size of the cavity inside the box can be tuned depending on the alkali metal used, a characteristic that gives this new family of compounds the potential to act selectively against different substrates. These compounds behave as active catalysts for disproportionation of H2O2 or for water photolysis, but they catalyze neither catecholase reaction nor peroxidase action upon using bulky organic substrates.

Unprecedent isolation of a mixture of conformational and linkage isomers in a thiosemicarbazone cobalt mesocate.

A cobalt(II) thiosemicarbazonate mesocate has been structurally characterized as an unexpected mixture of conformational and linkage isomers. Moreover, we have shown that the absence of a nitrogen atom in the spacer of the helicand ligand H(2)L(a), enables the assembly of an achiral mesohelical complex in the case of Co(II) ions.

Novel Manganese(III) Complexes with the Schiff Base N,N′‐(1,2‐Phenylene)‐bis(3‐Hydroxysalicylidenimine)

Four novel manganese(III) complexes have been prepared using the tetradentate ONNO symmetrical Schiff base N,N′‐(1,2‐phenylene)‐bis(3‐hydroxysalicylidenimine) H4L and employing different manganese(II) and manganese(III) starting salts (chloride, acetate, acetylacetonate and perchlorate). These complexes were thoroughly characterised by elemental analysis, ES mass spectrometry, infrared and paramagnetic 1H NMR spectroscopies, magnetic susceptibility measurements and molar conductivities. Electrochemical studies by cyclic and normal pulse voltammetry were also performed. All complexes obtained are manganese(III) ones, in which the anions belonging to the starting salts have diverse coordinating tendencies; this fact seems to determine the nuclearity of the final complexes, with empirical formulae [Mn(H2L)(H2O)2]Cl(H2O)3 1, [Mn(H2L)(OAc)](H2O) 2, [Mn(H2L)(acac)](H2O)3 3, and [Mn(H2L)(H2O)(CH3OH)](ClO4) 4. The X‐ray crystal structure of H4L Schiff base has been determined.

An unusual assembled Pb(II) meso-helicate that shows the inert pair effect

A dinuclear Pb(ii) mesocate has been prepared with an unprecedented four-coordinated kernel in which the Pb(ii) lone pair is stereochemically active. This is the first time that this effect has been observed in a supramolecular Pb(ii) helicate or meso-helicate.