Pedro Gili

Equilibria of chromate(VI) species in acid medium and ab initio studies of these species

Abstract The study of the H+ −CrO42− system in 3.0 M KCl as ionic medium at 25°C by means of emf (glass electrode) and direct calorimetric measurements, in the total CrVI concentration (B), average number of H+ bounds per central group CrO42− (Z), and pH ranges: 25 ⩽ B ⩽ 100 mM, 0 ⩽ Z ⩽ 1.16 and 1 ⩽ pH ⩽ 8, respectively, indicates the formation of the following complexes Hp(CrO4)q(p−2q), stability constants (logβpq(± 3σ)) and partial molar enthalpies (ΔHpq(±3 σ) kcal.mol−1): HCrO4−, 5.888(4), −0.6(1); Cr2O72−, 13.900(3), −5.7(1); H2CrO4, 7.004(7), 1.8(2) and HCr2O7−, 15.007(5), −5.0(1), respectively, according to the general reaction: pH+ + qCrO42− ⇄ Hp(CrO4)q(p−2q). The results previously obtained by Raman spectroscopy for this system are better adjusted when the HCrO4− species is included. The energies and optimized structures from ab initio calculations for the CrO42−, HCrO4−, Cr2O72−, H2CrO4 and HCr2O7− species have also been obtained. For the HCrO4− species the values of bond lengths and angles theoretically calculated are in good agreement with the experimental data of the anion in the crystal structure of the compound (PPh4)[CrVIO3(OH)]. Finally, correlations between thermodynamic experimental and structural theoretical parameters are discussed.

Magnetic Ordering in Two Molecule-Based (10,3)-a Nets Prepared from a Copper(II) Trinuclear Secondary Building Unit

Two new molecule-based materials of formulas 3D-{[K(H(2)O)(6)](0.5)[K(18-crown-6)](0.5)[MnCu(3)(Hmesox)(3)].5.25H(2)O} (1) and 3D-{(Ph(4)P)(2)[MnCu(3)(Hmesox)(3)Cl].3.5H(2)O} (2) have been prepared from a tricopper(II) secondary building unit (SBU), [Cu(3)(Hmesox)(3)](3-) (H(4)mesox = mesoxalic acid, 2-dihydroxymalonic acid). Compound 1 is obtained by means of the reaction of the SBU with manganese(II) acetate in the presence of potassium cations and the 18-crown-6 ether, whereas compound 2 is obtained by means of the reaction of the SBU with manganese(II) acetate in the presence of Ph(4)PCl. The [MnCu(3)(Hmesox)(3)](-) and [MnCu(3)(Hmesox)(3)Cl](2-) moieties in compounds 1 and 2, respectively, yield chiral 3-connected three-dimensional (3D) anionic (10,3)-a (srs, SrSi(2)) nets. In the cubic and centrosymmetric structures (Pa3) of 1, two inversion-symmetry-related anion nets interpenetrate to a racemic structure. The Ph(4)P(+) cations in 2 are organized in a supramolecular (10,3)-a net through the 6-fold phenyl embrace. In 2, both the cationic and anionic nets are homochiral and enantiopure with opposite handedness and form interpenetrating supramolecular and covalent (10,3)-a nets in the noncentrosymmetric Sohncke space group P 2(1)2(1)2(1). Both compounds display ferrimagnetic interaction with long-range magnetic ordering below 2.5 and 15.2 K for 1 and 2, respectively. A dehydrated phase of 2 exhibits a T(c) of 21.8 K. The saturation of magnetization, M(S), indicates two different ground states, S = (1)/(2) and (3)/(2), for the tricopper(II) units in 1 and 2, respectively. The different spin states of the tricopper(II) unit in 1 and 2 has been explained by means of a density functional theory (DFT) study performed in the [Cu(3)(Hmesox)(3)](3-) and [Cu(3)(Hmesox)(3)Cl](4-) fragments, for 1 and 2, respectively. A further DFT study has allowed one to analyze the structural parameters that lead to the different spin ground states for the trinuclear units in both compounds.

Emf(H) data analysis of weak metallic complexes using reduced formation functions

A general method for the study of weak metal complexes by emf(H) measurements has been developed using reduced formation functions instead of classical formation functions. This approach consists of subtracting the contribution of the products of the hydrolysis (protolysis) of the metallic cation (anion), as well as the possible protonated species of the ligand from the total number of associated H+, and from the total concentrations of metal or ligand, observing only the contribution of the reaction of interest. This was carried out using the FONDO version of the generalized least-squares computer program LETAGROP, written to analyze these reduced formation functions. The aim of this communication was to show in greater detail than in previous publications the data analysis of reactions in solution using these reduced formation functions. The method is illustrated using emf(H) data for the three-component systems H+–Be(II)–serine, H+–Mo(VI)–NTA and H+–V(IV)–V(V) investigated recently.

Hydrophobic-exterior layer structures and magnetic properties of trinuclear copper complexes with chiral amino alcoholate ligands

The trinuclear secondary building unit (SBU) {Cu3(μ-L)4X2} constructed from chelating and alcoholate-O-bridging chiral amino alcoholate (amino alkoxido, μ-L) and terminal halide ligands (X) gives rise to two-dimensional (2D) homochiral supramolecular polymers through the bridging action of the halide ligand. Compounds 2D-[Cu3(μ-L)4(μ3-X)2] {X = Br (1 to 4), X = Cl (5, 6); L = amino-ethanolate (1, 5), (R)-2-amino-propan-1-olate (2), (R)-2-amino-butan-1-olate (ab) (3, 6), (R)-2-amino-2-phenyl-ethanolate (4)} were synthesized from 2-amino alcohol, LH with CuBr2 or CuCl2, respectively, in the presence of triethylamine (TEA). The crystal packing of isomorphous 2D-[Cu3(μ-L)4(μ3-X)2] shows a separation of the hydrophobic alkyl from the hydrophilic amino-/alcoholate-/Cu–Br-region. Charge-assisted Cu(2+)⋯(−)Br- and hydrogen-bonding interactions in the hydrophilic region are the driving force of “hydrophobic exterior layer” formation with a hydrophilic interior exposing the hydrophobic alkyl groups to the exterior. Stacking of the layers through weak van-der-Waals interactions between the alkyl groups correlates with formation of thin crystal plates along the stacking direction. A lower ligand concentration yields both dinuclear and mononuclear SBUs in one-dimensional (1D-) homochiral coordination polymers 1D-[{Cu2(μ-ab)2Br2}2{(μ3-Br)Cu(abH)2Br}{(μ3-Br)Cu(abH)(CH3OH)Br}] (7) and 1D-[{Cu2(μ-ab)2Cl2}2{(μ3-Cl)Cu(abH)(CH3CH2OH)Cl}2] (8). In {[Cu(rac-abH)(rac-ab)H2O]ClO4}2 (9) two SBUs combine through charge assisted H-bonds to a dimeric unit. Temperature dependent magnetic susceptibility measurements of 1 and 3 show ferromagnetic coupling but no magnetic ordering. However, at temperatures lower than 3 K an onset of long-range magnetic ordering can be observed. AC magnetic measurements in the range of 1.9 K to 5 K at different frequencies show that the long range magnetic ordering is achieved at lower temperatures than that. Correlation of magnetic coupling with the Cu–O–Cu angle is in agreement with the structural parameters of 1 and 3. Very good agreement between experimental and DFT calculated J,j coupling constants shows that the interaction between the terminal copper(II) ions in these linear trinuclear SBUs is operative and it cannot be neglected.

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

Synthesis, spectroscopic, magnetic and electrochemical properties of Cu(II) and Fe(III) complexes with the new ligand N,N′-[1,1′-dithiobis(phenyl)]bis(5′-methoxysalicylaldimine)

Abstract The synthesis of N , N ′-[1,1′-dithiobis(phenyl)]bis(5′-methoxysalicylaldimine) (5MeOSalps) is reported, as well as its reactions with Cu(CH 3 COO) 2 ∗dH 2 O and anhydrous FeCl 3 to give [Cu(5MeOSalps)], [Cu(5MeOSalps)] 2 or [FeCl(5MeOSalps)], respectively, whose spectroscopic, magnetic, thermogravimetric, calorimetric and electrochemical properties have been studied and discussed in terms of N 2 O 2 S- or N 2 O 3 -type coordination for the monomeric and the dimeric complexes, respectively, the latter presenting two bridging phenoxide groups between the two Cu(II) ions. The dependence of the magnetic susceptibility on the temperature follows the Curie-Weiss law and no interaction between the copper ions is detected in the dimeric complex. As indicated by cyclic voltammetry and controlled potential electrolysis, in aprotic medium, the complexes undergo redox processes involving not only the metal redox pairs Cu(II)/Cu(III), Cu(II)/Cu(I) or Fe(III)/Fe(II), but also 5MeOSalps for which anodic processes centred at the phenolic or at the disulfide bridge, and cathodic processes localized at the latter group or at the imine moiety have been observed. The monomeric copper complex undergoes a chemically reversible two-electron reduction (with a quasi-reversible electrochemical character) which has been investigated by digital simulation and rationalized by considering a reversible molecular rearrangement which could involve the cleavage of a metal-sulfur bond.

Preparation and characterization of the dichromates of the organic bases: 2,4′-bipyridine, 2,2′-dipyridylamine and 4,4′-bipyridine

Abstract Dichromates of 2,4′-bipyridine (two forms), [(H2-2,4′-bipy)(Cr2O7)] (1) and [(H-2,4′-bipy)2(Cr2O7)] (2), 2,2′-dipyridylamine, [(H-dpam)2(Cr2O7)] (3), and 4,4′-bipyridine (two forms), [(H2-4,4′-bipy)(Cr2O7)] (4) and [(H-4,4′-bipy)2(H2-4,4′-bipy)(Cr2O7)2] (5), were prepared by reaction of chromium(VI) oxide with the free organic bases in the appropriate stoichiometric ratio in water at 25°C. The structures of compounds 2, 3 and 4 were determined by X-ray crystallography and revealed the existence of discrete dichromate anions formed by two tetrahedral CrO4 groups joined through shared O atoms, and the respective protonated organic bases hydrogen bonded to respective dinegative anions. A short CH…O interaction [2.996(4) A] between the organic cation and the dichromate anion was observed in compound 4. All organic dichromates were also characterized by IR, UV-vis 1H NMR measurements. For compounds 2, 3 and 4, a comparison was made and the crystallographic data of a series of mono- and polychromates and showed a correlation of the terminal and bridging CrO atomic distances with an increasing degree of polymerization. A graph theory cluster expansion was employed for these correlation studies.

Dimer complexes of 2,4-toluenediamine-N,N,N′,N′-tetraacetic acid (2,4-TDTA) with copper(II), nickel(II), cobalt(II), zinc(II) and manganese(II). Studies in aqueous solution and solid state. X-ray crystal structures of Na4[Ni2(2,4-TDTA)2]·15H2O and Na4[Cu2(2,4-TDTA)2]·20H2O

Abstract Potentiometric investigations in aqueous solution at 25°C and ionic strength 0.1 mol dm−3 KCl show that 2 2,4-toluenediamine-N,N,N′N′-tetraacetic acid (2,4-TDTA) forms with Cu(II), Ni(II), Co(II), Zn(II) and Mn(II) the following complexes (ligand, H4L): monomers [MH2L], [MHL]− and [ML]2−; dimers [M2HL2]3− and [M2L2]4−; with excess of ligand [MH2L2]4−, [MHL2]5− and [ML2]6− (Cu(II), Ni(II) and Zn(II)) and with excess of metal [M2HL]+ (Ni(II), Co(II)and Mn(II) and [M2L] (Cu(II)). The formation constants of the complexes have been determined. The species distribution diagrams indicate that a concentrated solution with a ligand:metal ratio 1:1 at pH 6 is suitable for the synthesis of crystalline salts of the dimetric complex species of Cu(II), Ni(II), Co(II), Zn(II) and Mn(II). X-ray diffraction structural analysis of the complexes Na4[Ni2(2,4-TDTA)2] · 15H2O and Na4[Cu2(2,4-TDTA)2]· 20H2O revealed that the dimer complex of Ni(II) is C1 and the dimer complex of Cu(II) is centrosymmetrical (C1). In both complexes each metal atom is surrounded by four carboxylic oxygens and two amine nitrogens in a distorted octahedron, for the Ni(II) complex, and an elongated bipyramid for the Cu(II) complex. X-ray diffraction analysis in powder was carried out for the complex Na4[Co2(2,4-TDTA)2] · 12H2O. The electronic properties have been characterised by spectroscopic techniques and variable-temperature magnetic susceptibility measurements. An orbital interpretation of the pathway of exchange interaction in this series of dimeric complexes is presented. The complexes were also characterised by mass and IR spectra and thermogravimetric analysis.

Molybdates of aromatic heterocyclic compounds. Synthesis and structure of an octamolybdate containing coordinately bound pyrazole: [(C3H4N2)2(Mo8O26)]4−

Abstract Molybdenum trioxide reacts with pyrazole to give the octamolybdate: (C3H4N2H)4[(C3H4N2)2(Mo8O26)]. The anion [(C3H4N2)2(Mo8O26)]4−, is built of two C3H4N2MoO5 and six MoO6 edge-sharing octahedra. The MoNNC3H4 bond length is 2.243(4) A, giving a bond strength of 0.35.

Complexes of Mn(II) and Mn(III) with the Schiff base N-[2-(3-ethylindole)]pyridoxaldimine. Electrochemical study of these and related Ni(II) and Cu(II) complexes

Abstract New complexes of Mn(II) and Mn(III) with the monoanionic bidentate ligand N-[2-(3-ethylindole)]pyridoxaldimine (pyrdoxTPA) are described. They are characterized by infrared and electronic spectroscopics, magnetic measurements and thermogravimetric and calorimetric studies. The spectroscopic and magnetic data indicate a tetrahedral coordination for the Mn(II) complex and a five-coordination for the Mn(III) complex. An electrochemical study of the Mn(II) and analogous Ni(II) and Cu(II) complexes with the same ligand is reported. As indicated by cyclic voltammetry and controlled potential electrolysis, in aprotic medium, the complexes display redox processes involving either the M(II)/M(III) (MMn, Ni or Cu) or the M(II)/M(I) (MNi or Cu) metal redox pairs, and the pyrdoxTPA ligands. The values of the redox potential of the metal centered redox processes follow the order of those of the corresponding ionization potential of the gaseous metal ions, and for the Mn(II) and Ni(II) complexes evidence is presented for the occurrence of anodically induced trimerizations.