Juan Manuel Arrieta

Crystal structures of two new heptamolybdates and of a pyrazole incorporating a gamma-octamolybdate anion

Two new heptamolybdates, one containing calcium and imidazole and the other with urea and ammonium cations, have been prepared. X-ray crystallographic studies of single crystals of both compounds have been carried out. In the mixture of calcium and imidazole [(Himi)(4)][Ca(H2O)(6)(mu-O)(2)][Mo7O24]. 2(imi). 3H(2)O (1), the calcium(II) cation is surrounded by six water molecules and two oxygen atoms from the polyanion, and bridges in trans position two [Mo7O24](6-) polyanions forming a linear composite with alternating Mo7O24 and Ca(H2O)(6) units. The urea compound [CO(NH2)H](3)(NH4)(9)[Mo7O24](2). 5[CO(NH2)(2)]. 4H(2)O (2) presents [Mo7O24](6-) heptamolybdate anions bound by hydrogen bonds from NH4+, [CO(NH2)H] cations and H2O molecules. A new crystalline phase of a gamma-octamolybdate containing pyrazole coordinatively bound to molybdenum has also been prepared [(Hpyr)(4)][(pyr)(2)(Mo8O26)]CH3COCH3. 2H(2)O (3). The structure has been solved by X-ray diffraction from a single crystal. The Mo-N bond length is 2.262(3) Angstrom. All compounds have been characterised by IR,H-1 NMR and thermal analysis

Sm(III) Complexation with amino acids. Crystal structures of [Sm2(Pro)6(H2O)6](ClO4)6 and [Sm(Asp)(H2O)4]Cl2

Samarium complexes with amino acids have been studied by potentiometric measurements. Experiments were performed in aqueous solution at 37.0 °C and 0.15 M NaClO4, resembling physiological medium. Low stability Sm(III)–amino acid complexes were detected. Complexes with 1 ∶ 1 ligand to metal molar ratios are predominant in the studied pH interval. Other mono- and di-nuclear species can be detected up to pH 6. For higher pH values, hydrolysis to [Sm(OH)]2+ and Sm(OH)3 becomes the main process. Some of the studied complexes were isolated and characterized in the solid state. Single-crystal X-ray structures of [Sm2(Pro)6(H2O)6](ClO4)6 (1) and [Sm(Asp)(H2O)4]Cl2 (2) are reported. In both complexes, an eight coordinate Sm atom is found, surrounded by carboxylate groups and water molecules. In 1, Sm atoms form infinite chains bridged by proline ligands (via carboxylate groups). An additional monodentate amino acid is present in the coordination sphere of each Sm center. In 2, the amino acid also bridges Sm atoms but using α and β carboxylate groups. The overall structure consists of infinite planes in which all carboxylate groups, acting as bidentate ligands, are bonded to Sm atoms.

Synthesis and characterization of new octamolybdates containing imidazole, 1-methyl- or 2-methyl-imidazole co-ordinatively bound to molybdenum

The compounds [H2im]4[Mo8O26(Him)2]1, [NH2Me2]4[Mo8O26(Him)2]·3H2O 2, [1-Hmim]4[Mo8O26(1-mim)2]·2H2O 3 and [2-Hmim]4[Mo8O26(2-mim)2]·3H2O 4(where Him = imidazole, 1-mim = 1-methylimidazole and 2-mim = 2-methylimidazole) have been synthesized. Compounds 1 and 3 were prepared by the reaction between molybdenum trioxide and imidazole or 1-methylimidazole in aqueous medium, whilst 2 and 4 were synthesized by reaction of molybdenum trioxide with imidazole or 2-methylimidazole in dmf–H2O (dmf = dimethylformamide). The compounds have been characterized by elemental analysis, infrared and 1H and 13C NMR spectroscopies and thermal measurements. The structures of compounds 2 and 3 were determined by X-ray crystallography and showed that both anions are composed of two MoNO5 and six MoO6 edge-sharing octahedra. The Mo–N and Mo–O bond strengths of both compounds have been calculated.

Dimer species in aqueous solutions of m–phenylenediamine-N,N,N′,N′-tetra-acetic acid (m-H4pdta) with copper(II) and of pyridine-2,6-diamine-N,N,N′,N′-tetra-acetic acid (2,6-H4pydta) with nickel(II). X-Ray crystal structures of Na4[Cu2(m-pdta)2]·18H2O, Na4[Co2(m-pdta)2]·10H2O, and Na4[Ni2(2,6-pydta)2]·8H2O

Potentiometric investigations in aqueous solution at 25 °C and ionic strength 0.1 mol dm–3 KCl have shown that the dimer complex species [Cu2L2]4–(ligand H4L, m-phenylenediamine-N,N,N,′N′-tetra-acetic acid, m-H4pdta) and [Ni2L2]4–(ligand H4L, pyridine-2,6-diamine-N,N,N′,N′-tetra-acetic acid, 2,6-H4pydta) are present in significant amounts at CM > 2 × 10–3 mol dm–3. The formation constants of the monomer and dimer have been determined. The formation of the dimer [M2L2]4– from the monomer [ML]2– or [M(HL)]– is affected by the Jahn–Teller effect (CuII–m-H4pdta) or by the effect of the withdrawal of electronic density by the pyridine nitrogen of the ring (NiII–2,6-H4pydta system). From a concentrated solution with a ligand: metal ratio of 1 : 1 at pH 6, single crystals of the complexes Na4[Cu2(m-pdta)2]·18H2O, Na4[Co2(m-pdta)2]·10H2O, and Na4[Ni2(2,6-pydta)2]·8H2O, respectively, were obtained. X-Ray diffraction structural analysis revealed that the dimer molecules are centrosymmetrical (Ci), with each metal atom surrounded by four carboxylic oxygens and two amine nitrogens in a distorted octahedron, the copper(II) complex being the most distorted (Jahn–Teller effect). In the nickel(II) complex the pyridine nitrogen is not bonded. Each sodium is co-ordinated to water molecules and carboxyl groups, being six-co-ordinated in the copper(II) complex and five-co-ordinated in the complexes of COII and NiII. The complexes were also characterized by i.r., electronic, and mass spectra, magnetic measurements, and thermogravimetric analysis.

The thermodynamics of the formation of Sm(III) mixed-ligand complexes carrying α-amino acids

Taking into account the low stability of the Sm(III)/amino acids compounds and searching for thermodynamically stable compounds which contain biologically relevant ligands in the coordination sphere, mixed-ligand compounds have been studied by potentiometric measurements. The strategy was to use a stable core with Sm(III) and polycarboxylates (edta, nta, ida, etc.) and to substitute the labile positions (occupied by water molecules) by amino acids. Experiments were performed in aqueous solution at 37.0 8C and 0.15 M NaClO4, resembling physiological medium. In all cases, mixed-ligand species were detected in solution. If cores like nta or ida were used, it was possible to get amino acid containing complexes stable enough to be used at physiological pH, avoiding precipitation of Sm(OH)3. Single-crystal X-ray structure of K2.5(H3O)0.5[Sm(nta)2(H2O)]/5H2O is also reported. A nine coordinate Sm atom is found, surrounded by two N atoms and six O atoms from two nta ligands and one O from a water molecule. Geometry around Sm can be described as a tricapped trigonal prism. # 2003 Elsevier B.V. All rights reserved.

Polymer species in aqueous solutions of para-phenylenediamine-N,N,N′,N′-tetraacetic acid (p-PhDTA) with cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II). X-ray crystal structure of Na4[Co2(p-PhDTA)2] · 8H20

Abstract Potentiometric investigations in aqueous solutions at 25°C and ionic strength 0.1 (CuII, NiII, CoII, ZnII and CdII) and 0.5 mol dm−3 KCl (CuII) analysed by LETAGROP and simulation calculus for a three-component system [Z(pH) curves] show that p-phenylenediamine-N,N,N′,N′-tetraacetic acid (p-PhDTA) forms protonated and non-protonated monomer and polymer complexes (ligand, H4L) at the concentrations and ligand: metal ratio studied: ratio 1 : 1, complexes HiMnLn(2n−2−i) n = 1–3,5,6 (CuII, NiII and CoII) and n = 1−3 (ZnII and CdII) ; with excess of metal complexes HnMn+1 Ln(2n−2−i−),n = 1 for all cations and n = 2, 3 for NiII and CoII; with excess of ligand, complexes HiMnLn+1(2n+ 4−i)−- with n = 1 mainly. The formation constants βpqr of the complexes have been determined and the Irving-Williams order of complexation is fulfilled. The species distribution diagrams indicate that the more important non-protonated polymer complexes are: trimer and pentamer for CuII; pentamer for NiII; dimer and trimer for CoII; trimer for ZnII and CdII. CoII, NiII; and CuII also form hexamers. From a concentrated solution with a ligand : metal ratio 2:3 at pH 5, single crystals of the complex Na4[Co2(p-PhDTA)2] · 8H20 were obtained. X-ray diffraction structural analysis revealed that in the the dimer anion [Co2(p-PhDTA)2]4− the cobalt atoms are hexa-coordinated with each metal surrounded by four carboxylic oxygens and two amine nitrogens (from two iminodiacetate groups) in a distorted octahedron. Each sodium is coordinated to water molecules and carboxyl groups, being five-coordinated.

Preparation and characterization of pyridinium-n-carboxylate trioxochromate (VI) (n=3, 4) and pyridinium-4-carboxylic pyridine-4 carboxylate trioxochromate (VI) hemihydrate

Abstract Three chromium (VI) compounds have been synthesized at room temperature by reaction of CrO3 with pyridinium carboxylic acids in water. An X-ray diffraction study of pyridinium-3-carboxylate trioxochromate, [3-HNicCrO3] (1), indicates crystallization in the triclinic system, space group P l (No. 2) with Z = 2 and lattice parameters a = 7.548(3) A , b = 6.593(3) A , c = 7.820(3) α = 90.01(2)°, β = 91.65(2)°, γ = 89.91(2)° and V = 389.0(3) A 3 at 25(2)°C. The chromium atom presents a distorted tetrahedral coordination, with the three CrO (terminal oxygen) bond lengths ranging from 1.588(6) A to 1.603(6) A, and the fourth CrO bond being 1.881(4) A long. The symmetry is C81 all atoms lying in the same plane with the exception of two terminal oxygens. 3-HNicCrO3 molecules interact by hydrogen bonds. This experimental work has been complemented with a theoretical study to discuss geometries, relative energies for the two possible isomers of compound 1, IR and UV-visible spectroscopic data, and electronic analyses. Powder data for pyridinium-4-carboxylic pyridine-4- carboxylate trioxochromate hemihydrate, [4-HNic][4-NicCrO3] (2), and pyridinium-4-carboxylate trioxochromate, [4-HNicCrO3] (3), are also reported.

Molybdotellurates containing the 1-methyl-, 2-methyl- and 4-methyl imidazolium cations

Four molybdotellurates containing the 1-methylimidazolium, 2-methylimidazolium and 4-methylimidazolium cations have been synthesized and their structures: [2-H2-methyl-imz]6[TeMo6O24 ]·2H2O (2), [2-H2-methyl-imz]6[TeMo6O24 ]·2(2-H-methyl-imz)·2H2O (3) and [4-H2-methyl-imz]6[TeMo6O24 ]·Te(OH)6 (4) determined by X-ray diffraction methods. The protonated organic bases are bonded to the anion in the crystal by hydrogen bonds, except for (4) where the crystal structure consists of discrete [TeMo6O24]6− anions and Te(OH)6 units, both bonded to 4-methylimidazolium cations by hydrogen bonds. The hydrogen bonds were studied as a function of the unit charge of the oxygen atoms of the [TeMo6O24]6− anion. Distortions of the central octahedron of polyanions of formula [XMo6O24]n− (X=AlIII, MoVI, TeVI and IVII), and polyanions of formula [H6YMo6O24]n−, (Y=CoII, CuII, ZnII, CrIII, RhIII and PtIV) are discussed. 95Mo n.m.r spectroscopy of compounds [1-H2-methyl-imz]6[Te-Mo6O24]·Te(OH)6 (1), (2) and (4) indicates the existence of an octahedral oxygen atom arrangement around the molybdenum and a pH variation experiment, carried out with compound (1), confirmed the existence of hydrolytic processes of the compounds in aqueous solution. 125Te n.m.r. studies permitted identification of the Te atom in the [TeMo6O24]6− kernel in all compounds; the presence of two different Te(OH)6 moieties in compounds (1) and (4) was also detected. The similarity between the spectra of both compounds could indicate that (1) has the same structural arrangement as (4). Finally, the thermal behaviour and the thermal stabilities of the complexes as a function of the organic cation were studied.

Crystal structure of (NH4)2[FeII5(HPO3)6], a new open-framework phosphite

(NH4)2[FeII 2(HPO3)6] exhibits an open-framework structure with channels in which disordered ammonium cations are situated.