Jose Ignacio Ruiz de Larramendi

Synthetic strategy, magnetic and spectroscopic properties of the terpyridine complexes [Cu(terpy)X(H2O)n]Y (X = NCO, NCS or N3; n= 0 or 1; Y = NO3 or PF6). Crystal structures of the azidenitrate and azidehexafluoro-phosphate

Eight copper(II) complexes with 2,2′:6′,2″-terpyridine (terpy) and pseudohalide ligands. [Cu(terpy)X-(H2O)n]Y [X = NCO, NCS or N3; n= 0 or 1; Y = NO3 or PF6] have been prepared by following a described synthetic strategy. The crystal structures [Cu(terpy)(N3)(H2O)]x[NO3]x and [Cu(terpy)(N3)-(H2O)]2[PF6]2 have been determined: monoclinic, space group P21/n, a= 8.849(2), b= 10.343(1), c= 18.168(3)A, β= 97.71(2)°, Z= 4; triclinic, space group P, a= 9.0609(6), b= 10.2798(8), c= 11.309(1)A, α= 105.22(7), β= 86.58(7), γ= 112.90(6)°, Z = 2. In both complexes [Cu(terpy)(N3)-(H2O)]+ entities are present. For the first compound these form a chain structure, via hydrogen bonding between the co-ordinated water molecule and the nitrate ion. However, the structure of the second compound is built from dimeric [Cu2(terpy)2(N3)2(H2O)2]2+ cations in which the copper ions are connected by one-end bridging azide groups and PF6– counter ions. The co-ordination geometry of the copper(II) ion is square pyramidal and octahedral for the two compounds respectively. The complexes studied can be grouped into three structural types, within each of which the compounds are isostructural. The anhydrous and hydrated hexafluorophosphates have dimeric structures; however, the nitrate compounds are associated in chains. Magnetic susceptibility measurements revealed weak magnetic interactions for all of them. The EPR spectra show ‘half-field’ forbidden transitions for all the complexes and even singlet-to-triplet forbidden transitions for the nitrates. From the positions of these last signals the exchange parameters for the nitrate compounds have been determined. The magnetic interactions have been analysed taking into account several exchange pathways.

Structure and spectroscopic study of an azide-copper(II) dinuclear complex : [Cu(pymep)(N3)2]2•2H2O

Abstract The compound of formula [Cu(C14H15N3)(N3)2]2·2H2O [where C14H15N3 is N-(2′-(6-methyl)pyridyl)methylene-2-(2

Crystal structure, spectroscopic and magnetic properties of two unusual compounds: [Cu(terpy)(N3)Cl] and [{Cu0.75Ni0.25(terpy)(N3)2}2]·2H2O (terpy = 2,2′ : 6′,2″-terpyridine)

The crystal structures of two unusual complexes [Cu(terpy)(N3)Cl]1 and [(Cu0.75Ni0.25(terpy)-(N3)2}2]·2H2O 2(terpy = 2,2′:6′,2″-terpyridine) have been determined at room temperature: 1. space group P21c. a= 10.586(5), b= 8.572(1), c= 16.396(3)A, β= 100.69(3)°, Z = 4, R=R′= 0.036, for 2818 reflections with I 3σ(I); 2, space group P21/c, a= 10.195(5), b= 9.996(3), c= 15.866(8)A, β= 91.10(5)°, Z= 4, R=R′= 0.055 for 3134 reflections with I 3σ(I). Complex 1 possesses the first known co-ordination polyhedron including both halide (Cl) and pseudohalide (N3) ligands. It shows a square-pyramidal topology for the copper(II), with the three nitrogen atoms of the terpy ligand and one terminal nitrogen atom of the azide group in the basal positions while the chloride atom is in the apical one. Compound 2 contains 25% of [{Ni(terpy)(N3)2}2]·2H2O and 75% of [{Cu-(terpy)(N3)2}2]·2H2O enclosed in the global lattice. It possesses (end-on) azide bridges and terminal azide ligands. The co-ordination polyhedron of the metal ion is a slightly distorted octahedron with the nitrogen atoms of the terpy ligand and a nitrogen atom of one of the azide bridging groups in the equatorial positions, while the nitrogen atoms of both the bridge and terminal azide groups occupy the axial positions. The pure copper phase related to compound 2 exhibits a discrete molecular topology; however, the pure nickel phase shows the same dimeric structure, which is useful for comparison. The magnetic properties of compound 2 can be explained by contributions from the isolated Cu2 and Ni2 entities, giving rise to global ferromagnetic interactions characterised by the parameters J= 20.1 cm–1, D=–12.5 cm–1, gNi= 2.26 and ρ= 0.76 corresponding to the copper proportion. The EPR measurements for both compounds reveal rhombic symmetries for the g tensors. Single-crystal EPR measurements on 2 show the presence of two magnetically different copper entities, with an antiferrodistortive ordering, in the lattice.

Structural and spectroscopic studies on the [Cu(C14H15N3)(NCS)2] complex. Stereochemistry of several five-coordinate copper(II) complexes with tridentate ligands

Abstract The title compound of formula [Cu(C14H15N3)(NCS)2] [where C14H15N3 is N-(2′-(6-methyl)pyridyl)methylene-2-(2′-pyridyl)ethylamine] has been synthesized and its crystal structure determined by X-ray diffraction. It shows isolated monomeric molecules with a near-trigonal bypyramidal geometry around the CuII ion, which is coordinated to three nitrogen atoms of the tridentate ligand and two nitrogens belonging to the isothiocyanato groups. Reflectance and ESR spectra are consistent with this structure. The stereochemistries of several [Cu(tridentate ligand)(unidentate ligand)2 five-coordinate complexes are discussed.

A novel one step synthesized Co-free perovskite/brownmillerite nanocomposite for solid oxide fuel cells

Cobalt-free perovskite oxides Pr1−xCaxFe0.8Ni0.2O3 (PCFN) were investigated as novel cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). Ca and Ni substitution in the PrFeO3 material shows that a wide range of perovskites Pr1−xCaxFe0.8Ni0.2O3 (0 < x < 0.9) can be prepared by sintering in air at 600 °C. Perovskites with 0 < x < 0.4 exhibit orthorhombic single phases (Pnma space group), whereas 0.4 < x < 0.9 show a coexistence of the perovskite and the brownmillerite-type structure (Ca2Fe2O5). The structure of the polycrystalline powders was analyzed by X-ray powder diffraction, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The analysis on the synthesized powders shows the presence of clusters formed by 30–100 nm nanoparticles. High-Resolution TEM (HRTEM) studies were carried out to confirm the existence of Ca2Fe2O5. The dc four-probe measurement exhibits a total electrical conductivity, over 100 S cm−1 at T ≥ 600 °C when 0 < x < 0.6, pointing out that strontium can be substituted for calcium without modifying the electrochemical properties. The Pr0.4Ca0.6Fe0.8Ni0.2O3/Ca2Fe2O5 composite cathode presents the better performance in electrochemical measurements, showing an area specific resistance value of 0.09 ohm cm2 at 850 °C.

Synthesis, crystal structure, stoichiometry and magnetic properties of (Ca1−xSrx)VO3

Abstract The alkaline-earth metal vanadium(IV) oxide system with formula (Ca 1−x Sr x )VO 3 has been synthesized using the metallo-organic method. The oxides prepared at temperatures of 1073–1173 K showed the presence of an oxygen excess while those obtained at higher temperatures (1273 K) where found to be stoichiometric. The crystal structure of these oxides (stoichiometric and non-stoichiometric) is perovskite with different symmetry depending on the strontium substitution: orthorhombic (0 ≤ x ≤ 0.2), tetragonal (0.3 ≤ x ≤ 0.4), and cubic (0.75 ≤ x ≤ 1). The influence of strontium substitution on the [VO 6 ] groups symmetry was also observed by vibrational spectroscopy. The electrical properties of the oxides are not extensively influenced by the stoichiometry and cation substitution.

Crystal structure and spectroscopic properties of a copper(II) complex with a chain arrangement : [Cu(pymep)Cl(H2O)](PF6)

Abstract A novel complex of copper(II) with the tridentate ligand N-[2′-(6-methyl)pyridyl]methylene-2-(2′-pyridyl)ethylamine (pymep), of formula [Cu(pymep) Cl(H 2 O)](PF 6 ), has been synthesized and its X-ray crystal structure determined. The structure consists of [Cu(pymep)Cl(H 2 O)] + cations and hexafluorophosphate anions. The copper complex is stacked to make a chain arrangement orientated in the [010] direction. The geometry of the coordination polyhedron around the copper(II) ion is close to tetrahedrally distorted square pyramidal (SP th ). One broad, unresolved band centred at 13,800 cm −1 is observed in the diffuse reflectance spectrum. The X-band ESR powder spectrum shows an orthorhombic signal with g 1 = 2.219, g 2 = 2.210 and g 3 = 2.047.

A straightforward synthesis of carbon nanotube–perovskite composites for solid oxide fuel cells

A powerful non-difficult and economical route based on the addition of carbon nanotubes (CNTs) is presented for the synthesis of nanostructured materials. For the first time, CNTs have been used as composite materials with a perovskite-type oxide for SOFC devices giving rise to an improved electrochemical behavior at intermediate temperatures.

Synthesis, crystal structure, spectroscopic and magnetic properties of strontium oxovanadium(IV) tartrate: molecular precursor for SrVO3

A new alkaline-earth-metal oxovanadium(IV) tartrate dimer with formula [Sr(VO)((±)-C4H2O6)(H2O)3]2 has been synthesized and characterized. The crystal structure consists of a three-dimensional (3D) arrangement of [(VO)((±)-C4H2O6)]24– dimeric anions, strontium cations and water molecules. There are several bonds between the oxygen atoms of the dimeric anions and the strontium cations, including a bond with the oxygen of the vanadyl group. The electron paramagnetic resonance (EPR) measurements show the dimeric nature of this complex. Thermal treatments of the compound, at low temperatures, yield different mixed oxides depending on the atmosphere employed. In air at 500 °C only the α-pyrovanadate is obtained while a thermal treatment in a hydrogen atmosphere at 900 °C is needed in order to obtain the SrVO3 oxide. The magnetic susceptibility of the SrVO3 phase revealed its metallic character.

Synthesis and characterisation of materials for solid oxide fuel cell cathodes

Solid Oxide Fuel Cells (SOFC) are one of the most promising future devices for energy production. New materials with better performance will be of crucial importance for their future development and commercialisation. This work summarises the basic operation principles of SOFCs and their material requirements. Samples of formula Gd0.7Sr0.3Mn0.8M0.2O3 (M = Cr, Ni) are used to show the research pathway followed for synthesis and characterisation of new materials as potential cathodes of SOFCs. Synthesis by sol-gel method and properties such as crystal structure, electrical conductivity and chemical compatibility with yttrium stabilised zirconia (8YSZ) electrolyte are discussed.