Gentilina Rossi

Two phthalocyanine units ‘stapled’ by carbon–carbon σ bonds in a new sandwich-type molecule: {5,5′;19,19′-bi[phthalocyaninato (2–)]}titanium(IV). Synthesis, X-ray crystal structure, and properties

{5,5′;19,19′-Bi[phthalocyaninato(2–)]}titanium(IV)–1-chloronaphthalene(1/1 ), [TiL]·C10H7Cl, is obtained by the reaction of [Ti(pc)Cl2](pc = phthalocyaninato dianion, [C32H16N8]2–) with Na2(pc) in 1-chloronaphthalene at 190 °C, An X-ray single-crystal structure (monoclinic, space group C/2c, a= 16.327(3), b= 18.568(4), c= 19.022(4)A; β= 94.50(1)°, Z= 4) indicates for this complex a sandwich-type structure with the titanium atom in the centre of the molecule and the two phthalocyaninato units ‘stapled’ by two inter-ring C–C σ bonds [C(11)–C(11′) 1.556(6) and C(31)–C(31′) 1.575(6)A]. Due to the staggered orientations of the two macrocyclic rings (relative rotation 45°) the planes of the two inner N4 systems (each of which is slightly distorted from planarity) form a square-antiprism, with an average interplane distance of 2.32 A(much shorter than that found in similar ‘unstapled’ complexes), and Ti–N bond distances in the range 2.17–2.26 A. The complex shows high thermal stability and can be oxidized by nitric acid to give the species [TiL]NO3. The complexes [TiL] and [TiL]NO3 show differing solid-state electrical conductivity properties.

Titanium and Ruthenium Phthalocyanines for NO2 Sensors: A Mini-Review

This review presents studies devoted to the description and comprehension of phenomena connected with the sensing behaviour towards NO2 of films of two phthalocyanines, titanium bis-phthalocyanine and ruthenium phthalocyanine. Spectroscopic, conductometric, and morphological features recorded during exposure to the gas are explained and the mechanisms of gas-molecule interaction are also elucidated. The review also shows how X-ray reflectivity can be a useful tool for monitoring morphological parameters such as thickness and roughness that are demonstrated to be sensitive variables for monitoring the exposure of thin films of sensor materials to NO2 gas.

Nitrido-bridged iron phthalocyanine dimers: synthesis and characterization

The synthesis of the µ-carbido species of formula (pcFe)2C (pc = phthalocyaninato dianion) has been accomplished by reaction of pcFe with Cl4, while reaction of (pcFe)2C with 1-methylimidazole produces an adduct of formula [(1-Meim)pcFe]2C; on the basis of i.r. and visible spectra and single crystal X-ray data, both species have been characterized as µ-carbido-bridged Fe dimers.

X-Ray crystal structure of µ-oxo-bis[(1-methylimidazole)-phthalocyaninatoiron(III)] and comments on the molecular structure and chemistry of oxo-bridged iron phthalocyaninate dimers

Single-crystal X-ray work has been carried out on crystals containing the 1-methylimidazole adduct of µ-oxo-bis[(phthalocyaninato)iron(III)], [{Fe(pc)(mim)}2O]·[Fe(pc)(mim)2]·3Me2CO. The crystals are monoclinic, space group C2/c, with a= 35.236(5), b= 14.173(2), c= 23.220(3)A, β= 103.56(10)° and Z= 4. The structure was solved and refined using all data including zero intensities (5739). Only the atoms of the µ-oxo dimer were refined anisotropically because of data limitations. The Fe atoms in [{Fe(pc)(mim)}2O] are nominally centred in the phthalocyanine plane, with an average Fe–N(pc) of 1.92(3)A and six-co-ordinate, with Fe–O 1.749(1)A and Fe–N(mim) 2.039(7)A. The Fe–O–Fe angle is 175.1°. X-Ray data for [Fe(pc)(mim)2] are as expected for six-co-ordinate low-spin nitrogen-containing base adducts of [Fe(pc)]. The crystal data are discussed in the light of similar results on [{Fe(pc)(mim)}2C] and related compounds.

Effect of nitrogen dioxide on titanium bisphthalocyaninato thin films

Thin films of Titanium bis-phthalocyaninato (TiPc2) are deposited on interdigital electrodes by evaporation under vacuum and have been investigated as semiconducting gas sensors. Oxidation of the films by NO2 is studied by visible absorption spectroscopy and IR spectroscopy of neutral and oxidised films. The variation at room temperature (RT) of electrical conductivity with different concentrations of NO2 has been investigated. The results describe the existence of a conductivity maximum during the oxidation. The analysis of the optical spectra of TiPc2 during NO2 adsorption and desorption gives the possibility to explain the change of the conductivity in terms of concentration of species present in the reaction.

Structural and morphological characterisation of ruthenium phthalocyanine films by energy dispersive X-ray diffraction and atomic force microscopy

Abstract Ruthenium phthalocyanine (RuPc)2, deposited as a film by vacuum sublimation onto a variety of substrates, was structurally and morphologically investigated by energy dispersive X-ray diffraction (EDXD) and atomic force microscopy (AFM) techniques. The attempt to apply the EDXD technique to amorphous films was successful and the reported results show the preservation of the Ru-Ru bond between two phthalocyanines units while transferring from the bulk to the film. The unidimensional arrangement of the dimeric phthalocyanine units in the film was observed to a larger extent than in the bulk; indeed 10 dimers were superimposed along the stacking direction (parallel to the RuRu bonds), while six units were found in the bulk material, the higher order being also supported by conductivity measurements. The amorphous nature of the film, anomalous in respect of the generally microcrystalline films of other metal phthalocyanines, was not changed by annealing the films at 170–200°C for more than 10 h. Reproducible and uniform deposition is identified by both EDXD and AFM data.

Effect of molecular packing on the solid state spectra of ruthenium phthalocyanine: anomalous behaviour of a monodimensional stacked assembly

The ruthenium phthalocyanine molecule has never been isolated as a single unit in the solid phase. Any attempt to obtain it leads to the dimeric form (RuPc)2 with a double bond between Ru–Ru atoms. Owing to the amorphous nature of this compound, its structural characterisation was previously investigated by LAXS (Large Angle X-ray Scattering) and EXAFS (Extended X-ray Absorption Fine Structure) studies. Magnetic and conductivity properties were also discussed in the light of the found structure. The optical spectra of the material in the solid phase and as evaporated films are reported in the present contribution. The obtained results show a marked red shifting absorption when passing from solution to film. Such anomalous behaviour can be explained taking into account the considerable molecular distortion presented by the two macrocycles within the dimer and, overall, considering the strong π–π interactions throughout the molecular stack. The attempt to apply the coupling exciton theory in order to clarify the optical data was not successful for the molecular assembly assumed by (RuPc)2 dimeric units. The EXAFS investigation on films, which supports the suggested interpretation, also shows some degree of flexibility of the molecule which somehow influences the whole molecular packing. Depth profile analysis of (RuPc)2 films, studied by the XPS (X-ray Photo-emission spectroscopy) technique, clearly indicates a homogeneity and a stable chemical composition throughout the thickness.

Interaction of phthalocyaninatoiron(II) with molecular oxygen. Kinetics and mechanism of the reaction in dimethyl sulphoxide

Abstract The reaction of phthalocyaninatoiron(II), FePc, with dioxygen in dimethyl sulphoxide solution has been studied kinetically by measuring the visible spectral changes occurring under high concentration conditions (h.c.c.: [FePc] = 1 X 10 −4 mol dm −3 or higher) and low concentration conditions (l.c.c.: 1 X 10 −5 mol dm −3 or lower). At h.c.c. the observed spectral variations (a decrease in intensity of the band at 653 nm and a parallel increase of a band at 620 nm) develop with an autocatalytic-like pattern and can be reversed either by nitrogen bubbling or dilution. The insoluble μ-oxo species (FePc) 2 O is the final reaction product. Under l.c.c. the spectral changes (a decrease in intensity of the spectrum at all wavelengths within the range 550–750 nm) are associated with an irreversible degradation of the complex. This spectral trend is also observed under h.c.c. when use is made of a free radical inhibitor (2,6-di(tert-butyl)-4-methylphenol). The whole experimental picture is satisfactorily explained by a mechanism in which an intermediate oxenic species FePcO can either react with FePc, to give reversibly the μ-oxo compound, or can oxidize the solvent (or a species derived from the solvent). In the h.c.c. reaction FePc behaves as an O-atom transfer catalyst.

Third-order optical non-linearities in titanium bis-phthalocyanine/toluene solutions

Abstract We report Z-scan experiments performed on titanium bis-phthalocyanine (TiPc 2 )/toluene solutions as a function of the molar concentration. The TiPc 2 cubic molecular hyperpolarizability, γ hyper , has been found to be (−70±30)×10 −32 esu at 800 nm, approximately 10 5 times larger in magnitude than the third-order susceptibility of the standard reference molecule CS 2 . Given the non-proximity of the laser wavelength to the main electronic bands of this molecule and its unusual molecular structure, we compare our results with previous measurements in other phthalocyanine systems. We also discuss the most probable factors influencing the non-linear optical response of our molecular system. The results indicate that the large non-linear optical response observed for TiPc 2 cannot be explained using optical-pumping, resonance-enhancement or electronic delocalization arguments.

Dioxygen activation and catalytic oxidation of triphenylphosphine by iron phthalocyanine compounds

Abstract The oxidation of PPh3 by molecular oxygen in toluene has been investigated through the use of phthalocyaninatoiron(II), (PcFe), and its corresponding bis-adducts of formula PcFe(N-base)2 (N-base = pyridine, 4-methylpyridine, piperidine, N-methylimidazole and imidazole) as catalysts. No oxidation was observed at 1 atm pressure, whereas both homogeneous and heterogeneous catalytic oxidation of PPh3 occurred at po2 = 60 - 70 atm at room temperature. Heterogeneous catalysis was observed with PcFe and PcFe(imidazole)2 which are both insoluble in toluene. Homogeneous catalysis in toluene solution was observed in all the other cases studied. The Nbase appears to play an important role in maintaining the conditions required for the Fe(II) ⇌ Fe(III) redox reaction. μ-Oxobis(phthalocyaninatoiron(III)), i.e. (PcFe)2O, appears to be the final oxygen-containing species formed by PcFe and its N-base adducts during the irreversible reaction involved. An ‘oxenic’ species of formula pyPcFeO is proposed as the intermediate active ‘oxygen atom transfer agent’ in the catalytic process, which seems to proceed via a non-radical pathway.