Lucilla Alagna

Porous cross-linked materials formed by oligomeric aluminium hydroxides and α-tin phosphate

The intercalation of the tridecameric polyhydroxyaluminium Keggin-type cation, formally [AlO4Al12(OH)24(OH2)12]7+, into α-Sn(HPO4)2·H2O via the colloidal tetramethylammonium-exchanged intermediate α-Sn[NMe4]0.9–1.0H1.1–1.0(PO4)2·4H2O and the alumina-pillared materials obtained after calcination are described. Two different intercalated precursor materials are obtained, depending on whether the Keggin ion inserted derives from the commercial product (‘Chlorhydrol’) or from the polyhydroxyaluminium cation generated in situ. Calcination leads to materials differing in free heights and in alumina contents. Their surface areas (B.E.T., N2, 77 K) are quite high: 190 m2 g–1[chlor-SnP (400 °C)] and 228 m2 g–1[Al13-SnP (400 °C)]. Pore-size calculations show them to be mainly mesoporous, but with some micropore contribution (> 50% of pores in width range 15–40 A). The higher microporosity of the former with respect to the latter is ascribed to lateral-order differences between the alumina pillars.High cation-exchange capacities (for Co2+, Ni2+ and Cu2+) confirm that both solids are porous and have more accessible interlayer sites than does the parent material. Optical spectra of the transition-metal ion-exchanged materials indicate that the sites available in the two solids differ, and that both differ from those present in the starting α-tin phosphate. Site geometries are suggested.

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.

Microscopic investigation of the strain distribution in InGaAs/GaAs quantum well structures grown by molecular beam epitaxy

Extended X-ray absorption fine structure in the glancing angle geometry has been used to study the strain accommodation in quantum well structures of In x Ga 1-x As/GaAs (x<0.25). The results show that a number of Ga-As bond lengths are stretched. Indeed, two Ga-As bonds distances coexist: 2.45±0.01 A and 2.64±0.02 A, which correspond to the Ga-As and In-As bond distances in the binary compounds GaAs and InAs, respectively. This result is independent of the In molar fraction in the strained alloy layers

A new layered vanadyl (IV) phosphate with an expanded interlayer

Abstract At high H 3 PO 4 : V 2 O 5 ratios (>4:1), the reaction of V 2 O 5 with H 3 PO 4 : EtOH at reflux for extended times gives rise to a material of formulation (VOHPO 4 ) 2 ·2.5H 2 O·EtOH. This material is thermally stable, and has a Stage I layered structure with a distance of 13.58 A between the vanadyl(IV)-phosphate containing planes. Spectroscopic evidence suggests that the EtOH molecule acts as a pillar holding these layers apart and that the stability is due to coordination of the ethanol to in-layer V(IV) atoms. Thermal decomposition of the material gives materials different than those given by the hemihydrate analogue VO(HPO 4 ) 2 0.5H 2 O. Such decomposition products may - in part at least - be responsible for many of the irreproducible results found during the preparation of precursors for the V-P-O catalysts adopted in the butane maleic anhydride conversion.

Diffraction anomalous fine structure of forbidden reflection of super-ordered GaInP.

We used DAFS to probe super-ordered domains in InGaP/GaAs epitaxial growth. The sample was lattice matched InGaP epitaxially grown on GaAs with a substrate miscut angle of 6 degrees with respect to the (001) direction. InGaP epi-layer exhibited (111)-type alloy ordering, of alternating InP and GaP like planes and giving rise to a (-5/2,5/2,-5/2) Bragg peak reflection which becomes allowed. Structural data can be extracted, at the same time, for the surroundings of Gallium in the bulk and in the epi-layer from allowed reflections, while the forbidden reflection gives structural details around Gallium in the ordered domains. Difference with the bulk InGaP Fourier transform confirms the symmetry selectivity of chosen reflections for the super-ordered domains.

Intercalation and co-ordination of ammonia and 1,2-diaminoethane into cobalt(II)-, nickel(II)-, copper(II)-, and vanadium(IV)-exchanged α-tin phosphate

The reactions of gaseous ammonia and 1,2-diaminoethane (en) with α-SnM(PO4)2·H2O (M = Co2+, Ni2+, Cu2+, or VO2+) have been investigated. Reactions occur with retention of the layered phosphate structure, the NH3-containing materials giving rise to an interlayer separation of 10.0 ± 0.05 A. Co-ordination of NH3 occurs in all cases except for VO2+(as deduced from electronic absorption spectra); Co2+ is present in a tetrahedral, probably CoN3O, environment not found in classical co-ordination chemistry, presumably as a consequence of the restricted space available in the interlayer. Ammonia co-ordinates to Ni2+ to give a cis-octahedral NiN3O3 environment and for Cu2+ a tetragonal octahedral environment, probably CuN2O2O′2. An extensive surface and interlayer complex chemistry is displayed by low (2%) loaded Cu2+-exchanged materials, for which e.s.r. studies have been made. The layer structure is retained on heating to 110 °C, stability to loss of ammonia being in the order: Cu2+ > Co2+ > Ni2+, with the greatest change in geometry for the partially dehydrated products occurring in the case of Ni2+ which adopts a five-co-ordinate environment. 1,2-Diaminoethane co-ordinates to both Cu2+ and Co2+, although only as a monodentate ligand; it does not appear to co-ordinate to either Ni2+ or VO2+, instead showing a tendency to hydrogen-bond to phosphate groups in the interlayer.

An EXAFS, and preliminary X-ray crystallographic, investigation of an iron-containing product from the lichen Cladonia deformis

An iron-containing product in the acetone extract from the lichen Cladonia deformis has been investigated using chemical, spectroscopic and X-ray crystallographic methods. Visible-near UV, EPR and IR spectra indicate that the iron is present as high-spin Fe(III) and coordinates in an oxygen-containing environment arising from graciliformin (or graciliformin-like) ligands. This has been confirmed by an XAS (X-ray absorption) study using synchrotron radiation. Comparison of the EXAFS and XANES results with those obtained from a model, tris(pent-2,4-dionato)Fe(III), and detailed fitting using the single-scattering, curved-wave formalism for the EXAFS strongly supports the presence of a Fe(III) coordinated to five oxygen atoms from the graciliformin.

ENDOR spectra of the intercalated water molecules in vanadyl(IV, V) phosphate pentahydrate

The ENDOR spectra of the metastable expanded layer solid VOPO4·5H2O and its congener VOPO4·2H2O [both containing very small amounts of vanadium (IV)] have been measured at 4 K. The latter gave no ENDOR, whereas the former provided a spectrum in which three different proton signals ascribable to two interlayer water molecules were detected. From a reconstruction of the interlayer, taking into account the layer expansion of 3.1 A due to the intercalated water molecules, it is suggested that VOPO4·5H2O is an example of a ‘pillared’ material.

Zirconium phosphates partially exchanged with transition-metal ions: characterisation and stereochemical changes induced by heat treatment

The α and γ forms of zirconium phosphate partially exchanged (between 20 and 90%) with Co2+, Ni2+, or Cu2+ have been characterised, and changes in stereochemistry about the metal ion followed using mainly electronic reflectance spectroscopy. The stereochemistries found in the room-temperature forms are the same as for the 100%-exchanged α form reported previously, i.e. octahedral. After heating these materials at 400 °C (i.e. when layer structures are still present), the stereochemistries about the metal ions are different from those in 100%-exchanged forms. Further heating, to 900 °C (destruction of layer structure), leads to further stereochemical changes. The other phases remaining in such materials thus influence the geometry of the cavity between the layers. Evidence is presented for the presence of five-co-ordinate geometries (both trigonal bipyramidal and square-based pyramidal) for Co2+- and Ni2+-containing materials.

Electron spin resonance spectrum of bis(4-phenylamino-2-phenyliminopent-3-enato-NN′)copper(II); a complex having both a low Azz and low-energy d-d band

Bis(4-phenylamino-2-phenyliminopent-3-enato-NN′)copper(II)(I), having a low energy d–d band characteristic of near-tetrahedral stereochemistry, shows an e.s.r. spectrum (as a doped sample of the zinc analogue) with a low A∥(Cu)(107 × 10–4 cm–1); the relevance of this spectrum to the stereochemistries proposed for ‘blue’ copper proteins is discussed.