Felipe Brito

Bio: Felipe Brito is an academic researcher from Central University of Venezuela. The author has contributed to research in topics: Aqueous solution & Stability constants of complexes. The author has an hindex of 16, co-authored 67 publications receiving 869 citations.

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

Abstract: 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.

Nitrilotripropionic Acid (ntp) and Other Polyamino Carboxylic-acids As Sequestering Agents for Beryllium(ii) - X-ray Crystal-structure of Sodium (nitrilotripropionato)beryllate(ii) Trihydrate, Na[be(ntp)]center-dot-3h(2)o

Abstract: Potentiometric studies in aqueous solution at 25 °C and ionic strength 0.5 mol dm−3 in NaClO4 show that beryllium(II) with different polyamino carboxylic acids forms the following complexes: EDTA (ethylenedi-aminetetraacetic), 1,2-PDTA (1,2-propylenediamine-N,N,N′,N′-tetraacetic), and CDTA (trans- 1,2-cyclohexanedi-amine-N,N,N′,N′-tetraacetic) (ligands, H4L), [BeHL]−, [BeL]2−, and [Be3(OH)3(HL)]; EDDADP (ethylenediamine-N,N′-diacetic-N,N′-dipropionic) and EDTP (ethylenediamine-N,N,N′,N′-tetrapropionic) (ligands, h4l), [BeH2L], [BeHL]−, [BeL]2−, and [Be3(OH)3(HL)]; o-PhDTA (o-phenylenediaimne-N,N,N′,N′-tetraacetic), 3,4-TDTA (3,4-toluenediamine-N,N,N′,N′-tetraacetic) and 4-Cl-o-PhDTA (4-chloro-o-phenylenediamine-N,N,N′,N′-tetraacetic) (ligands, ILL), [BeHL]− and [BeL]2−; NTA (nitrilotriacetic) (ligand H3L), [BeL]− and [Be3(OH)3(HL)]+; NDAP (nitrilodiaceticpropionic) (ligand H3L), [BeH2L]+, [BeHL], [BeL]−, [Be3(OH)3(HL)]+, and [Be3(OH)3L]; NADP (nitriloaceticdipropionic) (ligand, H3L), [BeHL] and [BeL]−; NTP (nitrilotripropionic) (ligand, H3L), [BeL]−. The following complexes are formed analogously for magnesium(II): O-PhDTA, 3,4-TDTA, and 4-Cl-o-PhDTA, [MgHL]− and [MgL]2−; NADP and NTP, [MgHL] and [MgL]−. The stability constants were determined. From an aqueous solution of Be(OH)2 and NTP (ratio 1:1), boiled until the Be(OH)2 was completely dissolved, crystals of the complex sodium (nitrilotripropionato)beryllate(II) trihydrate, Na[Be(NC9H12O6)]·3H2O were obtained. X-ray diffraction structural analysis revealed that, in the chelate complex [Be(NTP)]− (hexagonal), P63, a = 11.4768(7) A, b = 11.4768(7) A, c = 6.2807(3) A, V = 716.44(7) A3, Z = 2, R1 = 0.0433, wR2 = 0.1110), the tetrahedron BeN03 is almost regular with a very slight distortion toward the symmetry C3v. 1H, 13C, and 9Be NMR, IR spectra, and thermal analyses are studied. The selective uptake of beryllium(II), a very toxic cation, was analyzed by means of the chemical speciation diagrams as well as the so-called conditional or effective formation constants KBeLeff. With respect to H+, the order 3,4-TDTA ≥ o-PhDTA > 4-Cl-o-PhDTA ≥ NADP ≥ NTP ≫ NDAP > EDTA > EDTP > EDDADP is found for KBeLeff. This result indicates that, in competition with H+, o-PhDTA, 3,4-TDTA, 4-Cl-o-PhDTA, NADP, and NTP are good sequestering agents at pH 4.5–6 for beryllium(II), and analogously to o-PhDTA, these ligands can potentially be used for the analytical determination of beryllium(II). In the presence of Mg2+ and H+ (Be2+ inhibits numerous enzymes that compete with Mg2+), the order NTP ≈ NADP ≫ o-PhDTA ≈ 3,4-TDTA > 4-Cl-o-PhDTA is found. In the presence of Mg2+, at pH 4–6, NTP and NADP practically only sequester Be2+! The advantages of NTP and NADP acids to sequester specifically beryllium(II) are evident. 1H, 13C, and 9Be NMR studies confirm the Potentiometric studies. © 1995, American Chemical Society. All rights reserved.

Electronic Structure of Bis(o-iminobenzosemiquinonato)metal Complexes (Cu, Ni, Pd). The Art of Establishing Physical Oxidation States in Transition-Metal Complexes Containing Radical Ligands

Abstract: The ligand 2-anilino-4,6-di-tert-butylphenol and its 2-(3,5-dichloroanilino)-4,6-di-tert-butylphenol analogue react in CH3CN or CH3OH solutions with divalent transition metal ions in the presence of air and triethylamine. Depending on the metal:ligand ratio (1:1, 1:2, or 1:3) and the presence (or absence) of the cyclic amine 1,4-dimethyl-1,4,7-triazacyclononane (dmtacn), the following complexes have been isolated as crystalline solids: [CoIII(LISQ)3] (1); [CuII(dmtacn)(LISQ)]PF6 (2); [CuII(LISQ)2] (3); [NiII(LISQ)2] (4a); [NiII(ClLISQ)2] (4b); [PdII(LISQ)2] (5). (LISQ)- represents the monoanionic o-iminobenzosemiquinonate radical (Srad = 1/2). Compounds 1−5 have been characterized by single-crystal X-ray crystallography at 100(2) K. For all complexes it is unambiguously established that the O,N-coordinated o-iminobenzosemiquinonato(1−) ligand is present. Complexes 3, 4b, and 5 are square planar molecules which possess an St = 1/2, 0, and 0 ground state, respectively, as was established by 1H NMR and EPR ...

New avenues for ligand-mediated processes – expanding metal reactivity by the use of redox-active catechol, o-aminophenol and o-phenylenediamine ligands

Abstract: Correction for ‘New avenues for ligand-mediated processes – expanding metal reactivity by the use of redox-active catechol, o-aminophenol and o-phenylenediamine ligands’ by Daniel L. J. Broere et al., Chem. Soc. Rev., 2015, DOI: 10.1039/c5cs00161g.