Rui T. Henriques

Preparation and characterisation of new oxovanadium(IV) Schiff base complexes derived from amino acids and aromatic o-hydroxyaldehydes

Abstract A range of mostly new oxovanadium(IV) complexes is described. They contain coordinated Schiff bases, made from natural amino acids (glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, threonine, aspartic acid, and histidine) and salicylaldehyde or such derivatives as 3-, 4-, or 5-methoxy-salicylaldehyde. The coordination sphere is completed by simple ligands like water, 2,2′-bipyridyl or pyridine. The compounds are characterised and the nature of their coordination spheres shown by analysis, TLC, and by appropriate spectroscopy (EPR, IR, electronic and circular dichroism of solution and solids). In a few cases, magnetic properties are described to establish oxidation state. In several cases, the solubility of the compounds from racemic amino acids differs markedly from those containing the single enantiomer. The crystal and molecular structure of the related (and novel) compound with N-pyridoxylidene- d , l -isoleucinate, [VO(pyr- d , l -Ile)(bipy)]·H2O is described. It contains two diastereomers. Denoting the chiral vanadium centres as A or C, these are and [A(pyr- l -Ile)(bipy)] [C(pyr- d -Ile)(bipy)].

Gold complexes with dithiothiophene ligands: a metal based on a neutral molecule.

The gold complexes n-Bu4N[Au(alpha-tpdt)2] (5), n-Bu4N[Au(dtpdt)2] (4) and n-Bu4N[Au(tpdt)2] (6) based on new dithiothiophene ligands (alpha-tpdt= 2,3-thiophenedithiolate, dtpdt=2,3-dihydro-5,6-thiophenedithiolate and tpdt = 3,4-thiophenedithiolate) have been prepared and characterised. These gold(III) complexes are diamagnetic, but they can be oxidised with iodine to the paramagnetic compounds [Au(alpha-tpdt)2] (8), [Au(dtpdt)2] (7) and n-Bu4N[[Au(tpdt)2]n-2] (9), which were isolated as fine powders and which exhibit paramagnetic susceptibilities that are almost temperature independent with room temperature values of 2.5 x 10(-4), 2.0 x 10(-4) and 5 x 10(-4) emu x mol(-1), respectively. Interestingly, the neutral complex [Au(alpha-tpdt)2] (8) as a polycrystalline sample displays the properties of a metallic system with a room temperature electrical conductivity of 6 S x cm(-1) and a thermoelectric power of 5.5 microVK(-1); this is the first time that this metallic property has been observed in a molecular system based on a neutral species.

The [(DT‐TTF)2M(mnt)2] Family of Radical Ion Salts: From a Spin Ladder to Delocalised Conduction Electrons That Interact with Localised Magnetic Moments

Electrocrystallisation of the p-electron donor dithiopheno-tetrathia- fulvalene (DT-TTF) with maleonitrile dithiolate (mnt) - metal (M) complexes gives rise to the new family of radical ion salts ((DT-TTF)2M(mnt)2 )( MaAu, Pt, Ni), which are isostructural and crystal- lise in the monoclinic space group P21/n forming regular segregated stacks of donor and acceptor molecules along the b axis. The DT-TTF stacks are paired and interact strongly through S ··· S contacts in a ladder-like motif. The three salts have quite high room-temperature electrical conductivities (9, 40 and 40 S cm ˇ1 for Ma Au, Pt and Ni respec- tively) but their conductivity - tempera- ture dependencies differ. The Au salt has an activated conductivity at room temperature whereas the Ni and Pt salts are metal-like at room temperature and both exhibit a metal - insulator transi- tion around 120 K. These contrasting transport properties are accounted for by the differences in the transfer inte- grals along the DT-TTF stacks. The magnetic susceptibility of the salt with Ma Au, in which the (Au(mnt)2 ˇ ) anion is diamagnetic, can be fitted to a two- legged spin-ladder model. From diffuse X-ray scattering studies it is established that below 220 K the donors dimerise along the b stacking direction, and the spin carrier units in the ladder are identified as those formed by dimerised donors ((DT-TTF)2) a . . Observation in their EPR spectra of a single line which increases dramatically in width as the conductivity increases is evidence for the presence of two magnetic subsys- tems which interact in the salts (Ma Ni, Pt) with paramagnetic (M(mnt)2) ˇ ions.

Vanadium-salen and -salan complexes: Characterization and application in oxygen-transfer reactions

Salen complexes are a versatile and standard system in oxidation catalysis. Their reduced derivatives, called salan, share their versatility but are still widely unexplored. We report the synthesis of a group of new vanadium-salen and -salan complexes, their characterization and application in the oxidation of simple organic molecules with H2O2. The ligands are derived from pyridoxal and chiral diamines (1,2-diaminocyclohexane and 1,2-diphenylethylenediamine) and were easily obtained in high yields. The VIV complexes were prepared and characterized in the solid state (Fourier transform infrared, FTIR, and magnetic properties) and in solution by spectroscopic techniques: UV–vis, circular dichroism (CD), electron paramagnetic resonance (EPR), and 51V NMR, which provide information on the coordination geometry. Single crystals suitable for X-ray diffraction studies were obtained from solutions containing the VIV-pyr(S,S-chan) complex: [VVO{pyr(S,S-chen)}]2(μ-O)2·2(CH3)2NCHO, where the ligand is the “half” Schiff base formed by pyridoxal and 1S,2S-diaminocyclohexane. The dinuclear species shows a OVV(μ-O)2VVO unit with tridentate ligands and two μ-oxo bridges. The VIV complexes of the salan-type ligands oxidize in organic solvents to a VV species, and the process was studied by spectroscopic techniques. The complexes were tested as catalysts in the oxidation of styrene, cyclohexene, and cumene with H2O2 as oxidant. Overall, the V-salan complexes show higher activity than the parent V-salen complexes and are an alternative ligand system for oxidation catalysis.

Preparation and characterisation of new oxovanadium(IV) Schiff base complexes derived from salicylaldehyde and simple dipeptides

Abstract A range of mostly new oxovanadium(IV) complexes is described. They contain coordinated Schiff bases, made from simple dipeptides (glycylglycine, glycylsarcosine, l -alanylglycine, l -alanyl- l -alanine, d , l -alanyl- d , l -alanine and l -serylglycine), and salicylaldehyde. The compounds are characterised and the nature of their coordination spheres shown by analysis, TLC, by appropriate spectroscopy (EPR, IR, electronic and circular dichroism of solution and solids) and by magnetic susceptibility measurements. Serylglycine and threonylglycine are formed by reaction of VO(salGlyGly) with formaldehyde and acetaldehyde, respectively.

N-salicylideneamino-acidate complexes of oxovanadium(IV)—II. Synthesis, characterization and deamination of an n-salicylideneglycylglycinato complex

Abstract A vanadium(IV) complex VO(sal-glygly)(H 2 O) n ( 1 )(sal-glygly  N-salicylideneglycylglycinate; n = 1.5−3.0) has been isolated from relatively concentrated solutions containing oxovanadium(IV), glycylglycine and salicylaldehyde, and characterized by elemental analysis, thermal (TG and DSC), magnetic and spectroscopic techniques. From similar but dilute solutions the decavanadate, (NH 4 ) 4 (Na) 2 [V 10 O 28 ]·10H 2 O ( 2 ) was isolated after ageing: its structure has been determined by X-ray diffraction analysis. The NH 4 + cations were formed by deamination of the glycylglycine present in solution.

Preparation and characterisation of vanadium complexes derived from salicylaldehyde or pyridoxal and sugar derivatives

Abstract By reaction of salicylaldehyde (Hsal) with the amino-sugars d -glucosamine (glsmN), d -galactosamine (galacN) or d -glucamine (glcN) in the presence of VOSO4 or VOCl2, Schiff base (SB) complexes were obtained. By using pyridoxal (pyr) instead of Hsal, a solid containing the SB derived from its reaction with glcN was isolated. The compounds were characterised in the solid state by elemental analyses, IR, EPR, CD and magnetic susceptibility measurements. The complexes are not simple monomers in the solid state and were formulated as {VIVO(sal– d -galacN)}n, {VIVO(sal– d -glsmN)}n, (VIVVVO3)(sal– d -glcN) and (VIVO)3(pyr– d -glcN)2, the SB ligands being coordinated through the imine–N, phenolato-O−, sugar–O− and sugar–OH moieties. The complexes 3–5 were studied in solution by UV–Vis and CD spectrophotometry. The CD band pattern and λmax are normally the same both in the solid state and in MeOH, indicating that the binding mode is mostly preserved. Complex 6 is only slightly soluble and the spectroscopic studies were not conclusive in this respect. Upon dissolution of complexes 3–6, the oxovanadium(IV) is progressively oxidized and the SB hydrolysed.

High Magnetic Field Induced Charge Density Wave State in a Quasi-One-Dimensional Organic Conductor

The quasi-one-dimensional organic conductor (Per)2Pt(mnt)2 exhibits a charge density wave ground state below 8 K. Magnetoresistance and magnetization measurements show that the charge density wave is suppressed with magnetic fields of order 20 T, above which a high resistance state, with a cascade of subphases, appears. This new state, tentatively identified as a field induced charge density wave, reenters a low resistance state above 40 T. The results are presented in light of theoretical work [D. Zanchi et al. Phys. Rev. B 53, 1240 (1996)]] involving field induced charge density wave ground states in high magnetic fields.

The Interplay Between Conduction Electrons and Chains of Localised Spins in The Molecular Metals (Per)2M(mnt)2, M=Au, Pt, Pd, Ni, Cu, Co and Fe

The properties of the compounds of the family Per 2 M(mnt) 2 with α phases are reviewed taking into account recent experimental results. The perylene chins, responsible for electronic conduction undergo Peierls transitions at low temperatures. In the cases of M=Pt, Pd and Ni, the chins of M(mnt) 2 - units with localised spins have exchange interactions with the conduction electrons and undergo spin-Peierls transitions at the same temperatures. In the Fe compound only the Peierls transition occurs as the localised spins stacks are already in the ground state

Crystalline structure/transport properties relationship in the (perylene)2M(mnt)2 family M=Au, Pd, Pt, Ni)

Abstract We present the crystalline structures of (Perylene)2M(mnt)2 for M=Au and Pd (mnt=maleonitriledithiolate or cis-2,3-dimercapto-2-butenedinitrile, S2C2(CN)2). Both are monoclinic, space group P 2 1 c and isostructral with the Pt analog. We discuss the correlations between structure and transport properties of the above compounds.