J.C. Pedregosa

Ftir and mössbauer investigation of a substituted palygorskite: Silicate with a channel structure

Crystal data and spectroscopic studies of a silicate with a channel structure were realized. The substituted palygorskite from Las Quijadas (San Luis), Argentina, was studied by X-ray SBET, FTIR and Mossbauer spectroscopy. X-ray results clearly show that the investigated compound crystallizes in a monoclinic structure with space group C2m (C2h3, No. 12), and Z = 2. It is aluminium-rich and dioctahedral. Unit-cell parameters were determined using X-ray diffraction: a = 12.7 A, b = 17.9 A, c = 5.2 A, β = 91.86 °. The Mossbauer results prove that the very small amount of Fe(III) ions substituting Mg in the sample are located at two structural sites in the lattice. Through the FTIR spectrum analysis a more reliable assignment was performed with respect to tetrahedra, octahedra, hydroxyl groups and water molecules.

Raman investigation of A2CoBO6 (A=Sr and Ca, B=Te and W) double perovskites

Raman scattering is used to investigate the room temperature phonons of tetragonal (I4∕m) Sr2CoWO6 and monoclinic (P21∕n) Ca2CoWO6, Sr2CoTeO6, and Ca2CoTeO6 double perovskites. Both tetragonal and monoclinic structures result from small distortions of the Fm3¯m cubic lattice. Therefore, phonons were assigned according to correlations with those observed in the prototype A2B′B″O6 Fm3¯m cubic structure and the internal vibrational modes of the oxygen octahedra. The observed shifts of some vibrations in the A2CoBO6 compounds upon changing either A or B elements are tentatively explained.Raman scattering is used to investigate the room temperature phonons of tetragonal (I4∕m) Sr2CoWO6 and monoclinic (P21∕n) Ca2CoWO6, Sr2CoTeO6, and Ca2CoTeO6 double perovskites. Both tetragonal and monoclinic structures result from small distortions of the Fm3¯m cubic lattice. Therefore, phonons were assigned according to correlations with those observed in the prototype A2B′B″O6 Fm3¯m cubic structure and the internal vibrational modes of the oxygen octahedra. The observed shifts of some vibrations in the A2CoBO6 compounds upon changing either A or B elements are tentatively explained.

Spectroscopic behaviour of metal–drug complexes. Infrared spectra of Cu(II) complexes with 5-amino-1,3,4-thiadiazole-2-thiol (Hatm)

Abstract The infrared spectra of the drug Hatm and its copper (II) complexes with stoichiometry [Cu(atm) 2 (H 2 O)] and [Cu(Hatm)(HIm) 2 (SO 4 )] are reported and discussed. The Raman spectrum of Hatm is also reported. An assignment of Hatm, HIm, H 2 O and SO 4 modes in the complexes is proposed in comparison with the modes of the free ligands. Important information about the metal–ligand vibrations has been obtained.

Removal of oxovanadium(IV) from aqueous solutions by using commercial crystalline calcium hydroxyapatite

The interaction of oxovanadium(IV) (VO(2+)) in aqueous solution with commercial calcium hydroxyapatite (CAP) has been studied. VO(2+) ions are adsorbed on the surface of CAP by coordination to OH groups, without modification of the crystalline lattice. The extent of the adsorption is followed by chemical analysis, ESR and IR spectroscopy. Results are compared with those obtained for VO(2+)/synthetic calcium hydroxyapatite (HAP), reported by us in previous works. The uptake is better than the observed for HAP. The maximum adsorption is observed at pH 3.5 and 288 K. We conclude that VO(2+) is indeed adsorbed on CAP and the extent of adsorption depends on the pH and temperature.

An original polymorph sequence in the high-temperature evolution of the perovskite Pb2TmSbO6.

The synthesis, crystal structure, and dielectric properties of the novel double perovskite Pb(2)TmSbO(6) are described. The room-temperature crystal structure was determined by ab initio procedures from neutron powder diffraction (NPD) and synchrotron X-ray powder diffraction (SXRPD) data in the monoclinic C2/c (No. 15) space group. This double perovskite contains a completely ordered array of alternating TmO(6) and SbO(6) octahedra sharing corners, tilted in antiphase along the three pseudocubic axes, with an a(-)b(-)b(-) tilting scheme, which is very unusual in the crystallochemistry of perovskites. The lead atoms occupy a highly asymmetric void with 8-fold coordination due to the stereoactivity of the Pb(2+) lone electron pair. This compound presents three successive phase transitions in a narrow temperature range (at T1 = 385 K, T2 = 444 K, and T3 = 460 K in the heating run) as shown by differential scanning calorimetry (DSC) data. The crystal structure and temperature-dependent NPD follow the space-group sequence C2/c → P2(1)/n → R3 → Fm3m. This is a novel polymorph succession in the high-temperature evolution of perovskite-type oxides. The Tm/Sb long-range ordering is preserved across the consecutive phase transitions. Dielectric permittivity measurements indicate the presence of a paraelectric/antiferroelectric transition (associated with the last structural transition), as suggested by the negative Curie temperature obtained from the Curie-Weiss fit of the reciprocal permittivity.

Spectroscopic behavior of metal–drug complexes. Infrared spectra of Cu(II) dimer complexes with acetazolamide (H2acm) and an analogue sulfonamide (B-H2ats)

Abstract The infrared spectra of the drugs H2acm and B-H2ats, and their copper(II) dimer complexes with stoichiometries [Cu(acm)(NH3)2(OH2)]2·H2O and [Cu(B-ats)(NH3)2]2 are reported and discussed. The Raman spectra of H2acm and B-H2ats are also reported. An assignment of H2acm and B-H2ats modes in the complexes is proposed in comparison with the modes of the free ligands. The spectral modifications due to the deprotonation and coordination effects are analyzed. The ν(N–H) modes of the sulfonamido, carbonamido and Nring–H of the imine tautomer have been accurately assigned. Important information about the S–O and S–N vibrations has been obtained.

The role of the Pb2+ 6s lone pair in the structure of the double perovskite Pb2ScSbO6

The new double perovskite Pb2ScSbO6 was synthesized by standard ceramic procedures; the Rietveld refinement of room temperature neutron powder diffraction data shows that the crystal structure is well defined in the space group Fm3[combining macron]m. It contains a completely ordered array of alternating ScO6 and SbO6 octahedra sharing corners; the PbO12 polyhedra present an off-center displacement of the lead atoms along the [111] direction, due to the electrostatic repulsion between the Pb2+ 6s lone pair and the Pb-O bonds of the cuboctahedron. Dielectric permittivity measurements show a peak near 343 K, with a Curie-Weiss response above this temperature, which suggests an antiferroelectric behavior. Finally we present a DFT study of the electronic structure of Pb2ScSbO6, showing a great difference between the electronic density within SbO6 and ScO6 octahedra.

Crystal and magnetic structure of the double perovskite Sr2CoUO6: a neutron diffraction study

Sr2CoUO6 double perovskite has been prepared as a polycrystalline powder by solid-state reaction, in air. This material has been studied by X-ray, neutron powder diffraction (NPD) and magnetic measurements. At room temperature, the crystal structure is monoclinic, space group P2(1)/n, Z= 2, with a= 5.7916(2), b= 5.8034(2), c= 8.1790(3) A, beta= 90.1455(6)degrees. The perovskite lattice consists of a completely ordered array of CoO6 and UO6 octahedra, which exhibit an average tilting angle phi= 11.4 degrees. Magnetic and neutron diffraction measurements indicate an antiferromagnetic ordering below TN = 10 K. The low-temperature magnetic structure was determined by NPD, selected among the possible magnetic solutions compatible with the P2(1)/n space group, according with the group theory representation. The propagation vector is k= 0. A canted antiferromagnetic structure is observed below TN = 10 K, which remains stable down to 3 K, with an ordered magnetic moment of 2.44(7)mu(B) for Co2+ cations. The magnetic moment calculated from the Curie-Weiss law at high temperatures (5.22 mu(B)/f.u.) indicates that the orbital contribution is unquenched at high temperatures, which is consistent with high-spin Co2+((4)T(1g) ground state) in a quasi-regular octahedral environment. Magnetic and structural features are consistent with an electronic configuration Co2+[3d(7)]-U6+[Rn].

SEVERAL COORDINATION MODES OF 5-AMINO-1,3,4-THIADIAZOLE-2-SULFONAMIDE (HATS) WITH Cu(II), Ni(II) AND Zn(II): MIMETIC TERNARY COMPLEXES OF CARBONIC ANHYDRASE-INHIBITOR

Abstract The coordination properties of 5-amino-1,3,4-thiadiazole-2-sulfonamide (Hats) with Cu(II), Ni(II) and Zn(II) ions, are analyzed. Although the ligand presents several donor atoms, we have only observed three coordination behaviors: (i) as a monodentate ligand through the Nsulfonamido atom, (ii) as a bridging ligand linking the metal ions through the Nsulfonamido and Nthiadizole atoms and (iii) as a bridging ligand linking metal ions through the N and O atoms of the sulfonamidate group. It is noteworthy that coordination mode (iii) is observed for the first time in heterocyclic sulfonamides complexes. In addition, the conformation of the Hats as counter-ion is analyzed and compared with the conformations that the ligand adopts in metal complexes.

Structure of 5-amino-1,3,4-thiadiazole-2-sulfonamide, an inhibitor of the enzyme carbonic anhydrase

Bond lengths and angles indicate a strong interaction between the NH 2 group and the thiadiazole ring. The sulfonamido moiety adopts a distorted arrangement around the S atom. Structural features of the com pound are compared with those of acetazolamide, N-[5-sulfamoyl-1,3,4-thiadiazol-2(3H)-ylidene]- acetamide (H 2 acm), methazolamide, N-[3-methyl 5-sulfamoyl- 1,3,4-thiadiazol-2(3H)-ylidene]acetamide (Hmacm), and 5-amino- 1,3,4-thiadiazole-2-thiol (Hatm)