Miguel Vázquez

A two-channel molecular dosimeter for the optical detection of copper(II)

A cyclam-like macrocycle with an integrated push-pull chromophore selectively detects Cu2+ inclusion through both orange-to-yellow colour change and quenching of the green fluorescence.

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.

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.

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.

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.

Further insights on the high–low spin interconversion in nickel(II) tetramine complexes. Solvent and temperature effects

The spin interconversion equilibrium involving the [Ni(II)(cyclam)]2+ complex has been investigated in a variety of polar solvents, at varying temperatures. The greater the donor tendencies of the solvent, the higher the endothermicity of the high-to-low-spin conversion. In particular, a positive linear relationship exists between DeltaHdegrees and Gutmanns Donor Number (DN). In the same way, higher donor tendencies of the solvent favour the occurrence of the Ni(II)-to-Ni(III) oxidation process and negative linear relationship has been found between the E1/2(Ni(III)/Ni(II)) and DN. General behaviour is related to the intensity of the metal-solvent axial bonds in the octahedrally elongated cyclam complexes (of both Ni(II) and Ni(III)).

N,N′-Bis(2-tosyl­amino­benzyl­idene)-1,2-ethanedi­amine

The structure of the title compound, C30H30N4O4S2, is highly conditioned in the solid state by two strong N—H⋯N interactions. The values of the distances between the aminic N atoms [5.865 (3) A] and the iminic N atoms [2.930 (4) A], in conjunction with the long distance between the S atoms of the two tosyl groups [7.673 (1) A], suggest that when the molecule acts as a ligand it will provide a single cavity for N4 coordination to the metal centre.

Molecular Devices Based on Metallocyclam Subunits

Publisher Summary This chapter explains that metal complexes of cyclam derivatives, including scorpionands, can perform some elementary functions at the molecular level (signalling, sensing, controlling of molecular motions). These, and other, functions result from the combination of the unique properties displayed by cyclam and related synthetic macrocycles. Cyclam (1,4,8,11-tetra-aza-cyclotetradecane, 3) is the prototype of synthetic aza-macrocycles. It tends to encircle transition metal ions to give complexes of trans-octahedral geometry, which display some peculiar properties: (i) high thermodynamic stability (the thermodynamic macrocyclic effect); (ii) extreme inertness to demetallation (the so-called kinetic macrocyclic effect); (iii) rich redox activity of the metal centre and stabilization of unusually high oxidation states: Ni III , Cu III , Ag II and Ag III and, as a transient, Hg III . The chapter discusses various properties that make cyclam and its metal complexes convenient and versatile subunits for building multicomponent systems displaying a variety of functions. The 2-substituted positional isomer is expected to favor the coordination of the nitro–nitronate group to transition metal centre, encircled by the cyclam ring.

N,N'-bis(2-tosylaminobenzylidene)benzene-1,2-diamine

The conformation of the title compound, C34H30N4O4S2, is strongly influenced by intramolecular N—H⋯N hydrogen-bond interactions and by the rigidity endowed by the presence of a phenyl group between the imine N atoms. The molecule is not planar, with very short distances between the imine N atoms [N⋯N 2.753 (3) A] and the amine N atoms [N⋯N 5.148 (4) A]. Consequently, important changes in its conformation will be required if it is to act as a tetradentate ligand via its four N atoms.