Erasmo Chinea

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.

Preparative, potentiometric and NMR studies of the interaction of beryllium(II) with oxalate and malonate. X-ray structure of K3[Be3(OH)3(O2C–CH2–CO2)3]·6H2O

Abstract The complexes formed by beryllium(II) with the bidentate ligands oxalate, L=(O2C–CO2)2−, and malonate, L=(O2C–CH2–CO2)2−, have been investigated in aqueous solution using both potentiometric and 9Be NMR measurements. The species [BeL(H2O)2], [BeL2]2−, [Be3(OH)3L3]3− and [Be3(OH)3(H2O)3L]+ have been identified and their formation constants have been determined at 25°C in 0.5 mol dm−3 NaClO4. The malonate complexes are much more stable than the oxalate ones. New crystalline salts of formula K3[Be3(OH)3L3]·nH2O have been isolated using conditions established with the aid of speciation calculations. The structure of K3[Be3(OH)3(malonate)3]·6H2O has been determined by an X-ray structure analysis: orthorhombic, space group Pc21n, a=9.011(3), b=14.041(4), c=18.761(9) A, Z=4. Each beryllium atom is tetrahedrally coordinated by two hydroxo groups and two oxygen atoms from the chelating malonate. The (Be(OH))3 core is a puckered six-membered ring with each hydroxo group bridging two beryllium centres.

Mixed-ligand copper(II) complexes with N-methyl derivatives of iminodiacetato or imidazole: crystal structures of (N-methyl-iminodiacetato) (imidazole) copper(II), [Cu(MIDA) (ImH)] and diaqua (iminodiacetato) (N-methyl-imidazole) copper(II) monohydrate, [Cu(IDA) 1 MeImH) (H2O)2] · H2O

Equimolar (1:1:1) mixed-ligand Cu(II) complexes with iminodiacetato (IDA) or N-methyl-IDA (MIDA) and N-methyl-imidazole (1MeImH) or ImH, respectively, have been prepared and characterized by thermal, spectral, magnetic and X-ray diffraction methods. [Cu(MIDA) (ImH)] (I) crystallizes in the monoclinic system P21/n (a = 12.465(3), b = 5.999(1), c = 14.733(3) A, β = 111.91(1)°, Z = 4, R = 0.043, Rw = 0.047). The Cu(II) atom exhibits a flattened square base byramidal coordination (type 4 + 1). The N and two O atoms of the tridentate MIDA and one N of ImH form the square base; one longer CuO bond with the next MIDA ligand in the chain complex completes the Cu(II) five-coordination. [Cu(IDA) (1MeImH) (H2O)2]·H2O (II) crystallizes in the orthorhombic system Pna21 (a = 14.733(2), b = 7.721(1), c = 11.288(1) A, Z = 4, R = 0.041, Rw = 0.043). The N and two O atoms from IDA and one N from 1 MeImH define a square coordination; two longer CuOH2 bonds complete the unsymmetrical elongated octahedral coordnation of Cu(II) (type 4 + 1 + 1). The polar NH bonds of ImH in I and of IDA in II as well as the OH bonds of the water molecules of the latter compound are involved in hydrogen bonds. The stepwise water loss in II is explained on the basis of its structural role in the Cu(II) coordination and/or in the crystal packing.

Synthesis, crystal structure, thermal and magnetic properties of [Mn(H2O)6][Cu(pdta)]·2H2O (pdta=1,3-propylenediamine-N,N,N′N′-tetraacetate)

Abstract On mixing concentrated aqueous solutions of pdta, Cu(II) and Mn(II) in the ratio 1:1:1 at pH 4.5, single crystals of the complex [Mn(H2O)6][Cu(pdta)]·2H2O (1) (pdta=1,3-propylenediamine-N,N,N′N′-tetraacetate) were obtained. X-ray structural analysis revealed that in the anion [Cu(pdta)]2− the coordination polyhedron around the Cu(II) ion can be described as a tetragonaly distorted CuN2O4 octahedron, whereas the cation [Mn(H2O)6]2+ can be described as a very regular MnO6 octahedron. Thermogravimetric analysis shows that at 110°C compound 1 loses its eight water molecules yielding the anhydrous compound [MnCu(pdta)] (2). Variable-temperature magnetic susceptibility measurements indicate that no magnetic interactions are present in 1 while weak antiferromagnetic interactions occur in 2.

Synthesis, characterization and potentiometric studies of trans-dioxorhenium(V) complexes. X-ray crystal structure of [ReO2(tn)2]I·H2O

Abstract [ReO2(PPh3)2I] has been used as starting material to prepare [RevO2(tn)2]I (tn = trimethylenediamine) in high yield. The complex was characterized by elemental analysis and spectroscopic methods. The complex [ReO2(en)2]I (en = 1,2-diaminoethane) was prepared analogously for comparison. The crystal structure of [ReO2(tn)2]I·H2O was determined from X-ray data. It consists of a six-coordinate rhenium atom bonded to two trans-oxo groups. The amines lie in the equatorial plane, almost perpendicular to the ReO2 core. The average value for the ReO bond is 1.76 A, similar to that in other Re(V) dioxo complexes. The successive protonations of the oxo groups were determined for both complexes.

REVIEW: NEW ADVANCES IN THE COORDINATION CHEMISTRY OF THE BERYLLIUM(II)

Abstract Beryllium and its compounds are extremely toxic, but the biological mechanism of their toxicity is largely speculative. Beryllium is the second lightest metal after lithium and it is a component of materials indispensable in todays nuclear, aerospace and electronic industries. Concern about possible pollution by beryllium-containing materials is renewing interest in the chemistry of the metal. Therefore, there is much interest in the search for suitable ligands as antidotes for beryllium poisoning. The more recent studies on the coordination chemistry of beryllium(II) have concentrated attention on ligands of the following types: (a) ligands with oxo, oxocar-boxylic or carboxytic groups; (b) ligands with carboxylic-phosphonic or phosphonic groups; (c) polyaminocarboxylic ligands as sequestering agents.

Synthesis and characterization of (NH4)4[H4V10O28][NTPH2]2·4H2O (NTPH3=N(CH2CH2COOH)3)

Abstract Reaction of (NH4)VO3 with NTPH3 (N(CH2CH2COOH)3) in water, at controlled pH, allowed the synthesis of (NH4)4[H4V10O28][NTPH2]2·4H2O salt, which has been characterized by spectroscopic measurements (NMR), electrospray mass spectrometry (ESMS) and X-ray diffraction studies. The structure is strongly stabilized by an extensive network of hydrogen bonding interactions which involve the tetraprotonated decavanadate anion, NTPH2 ligand anions, ammonium cations and solvent water molecules.