Rosa Pedrido

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 3D network of helicates fully assembled by π-stacking interactions

The neutral dinuclear dihelicate [Cu2(L)2] x 2CH3CN (1) forms a unique 3D network in the solid state due to pi-stacking interactions, which are responsible for intermolecular antiferromagnetic coupling between Cu(II) ions.

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].

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.

Factors involved in the nuclearity of silver thiosemicarbazone clusters: cocrystallization of two different sized tetranuclear silver(I) clusters derived from a phosphinothiosemicarbazone ligand.

The reaction of silver acetate with a phosphinothiosemicarbazone ligand, HLPPh, yielded the tetranuclear silver compound [Ag 4(LPPh) 4].2MeOH ( 1), which after recrystallization results in the cocrystallization of two different silver clusters, [Ag 4(LPPh) 4] (a)[Ag 4(LPPh) 4] (b).8MeOH ( 2). The factors involved in the assembly of tetranuclear compounds derived from thiosemicarbazone ligands and the structural differences between the two clusters are analyzed herein. Additionally, HLPPh and complex 1 exhibit photoluminescence in solution at room temperature.

Novel Fluorescent Cationic Silver Thiosemicarbazone Clusters Containing Different Eight-Membered Ag4S4 Metallacycles

The reaction of silver acetate and silver nitrate with the new phosphinethiosemicarbazone ligand 2-(2-(diphenylphosphino)benzylidene)-N-ethylthiosemicarbazone (HLPEt) gave rise to the complexes [Ag(LPEt)](4).2MeOH (1) and [Ag(2)(LPEt)(HLPEt)](2).(NO(3))(2) (3). Slow crystallization of the mother liquors obtained from the synthesis of 1 and 3 afforded suitable crystals of [Ag(2)(LPEt)(HLPEt)](2)(CH(3)COO)(2).6MeOH (2) and [Ag(2)(LPEt)(HLPEt)](2)(NO(3))(2).2MeOH.2H(2)O (4), respectively. Complexes 2 and 4 are tetranuclear silver clusters displaying a similar Ag(4)S(4)P(4) core, but containing different sizes, conformations for the Ag(4)S(4) metallacycles, and crystal packings. The four complexes are strongly luminescent in methanol solutions. A comparison between the emission bands of compounds 1-4 lead us to conclude that the luminescence is notably affected by the charge and the counterion of the cluster.

A thiosemicarbazone ligand functionalized by a phosphine group: Reactivity toward coinage metal ions

The reactivity of the phosphino-thiosemicarbazone ligand 2-(2-(diphenylphosphino)benzylidene)-N-ethylthiosemicarbazone (HLPEt) toward M(I) halides (M = Cu, Ag, Au) was studied. The complexes obtained, with formulae [Cu(HLPEt)(2)]Br (1), [Cu(HLPEt)(2)]I.2H(2)O (2), [Ag(HLPEt)(LPEt)].3H(2)O (3), [Au(2)(HLPEt)(2)Cl]Cl.CH(3)OH (4) were satisfactorily characterized by elemental analysis, IR, ESI and (1)H/(31)P NMR. Moreover, we have obtained the crystal structure of the ligand HLPEt and its sulfide oxidized form HLP(S)Et, which represents a new case of desulfurization process in thiosemicarbazone ligands. In addition, we present the crystal structure of the complexes 1 + H(2)O + 3MeOH and [Au(2)(HLPEt)(4)Cl]Cl.3CH(3)OH (5), together with their interesting crystal packing. The complex 5 is an interesting case of a pseudo-chloronium gold(I) complex. The ligand HLPEt and the complexes 3 and 4 display intense luminescence at room temperature.

A metallo-supramolecular approach to a half-subtractor

The tetraamine dinucleating ligand L, which bears naphthalene moieties at both ends, behaves as a combinatorial logic circuit for a molecular half-subtractor in the presence of ZnII ions.

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.