Maria A. A. F. de C. T. Carrondo

Instituto Técnico y Cultural, Santa Clara de Portugal, Michoacán, Mexico

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Publications (15)39.82 Total impact

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    ABSTRACT: Electronic and ESR spectroscopic studies in aqueous solution and single-crystal X-ray diffraction analyses of copper(i1) complexes of the following oxatriaza macrocycles have been undertaken: I -oxa-4.7,lOtriazacyclododecane ( L1), 4.7.1 0-trimethyl-I -oxa-4.7.10-triazacyclododecane ( L2), 1 -oxa-4.7.11 -triazacyclotridecane ( L3), 1 -oxa-4,8,12-triazacyclotetradecane ( L4), and 4,8,12-trimethyI-l -oxa-4,8,12- triazacyclotetradecane ( L5). The complexes for solution studies were prepared in an excess of NaCIO,, but the bulky counter ion PF,- was added io induce crystallization. The crystal structures of [CuL1(Br)] [PF,], [CuL2(CI)] [PF,], [CuL'(H,O)] [PF,],. H,O and [CuL5(CI)] [PF,] were determined. The co-ordination geometry aroufid the copper atom in the four complexes can be described as a distorted square pyramid, but whereas the basal planes comprise the three nitrogens and the oxygen from the macrocycle in the last two complexes, in the first two complexes they comprise the three macrocyclic nitrogens and a halogen atom, bromine and chlorine respectively. The apical co-ordination in the latter is by the macrocyclic oxygen, but in [CUL~(H,O)][PF~]~*H,Oit is the oxygen of a water molecule and in [CuL5(Cl)][PF6] it is a chlorine atom. The main conclusions on the structures of these complexes from spectroscopic measurements and X-ray studies are in good agreement. However, for the complex of the 13-membered macrocycle (L3) published X-ray results point to a structure similar to those found in this work for the 14-membered macrocyclic complexes, while the spectroscopic studies now reported indicate a structure with a pronounced tetrahedral distortion similar to that observed in the 12-membered macrocyclic complexes. The replacement of hydrogen atoms by methyl groups on the nitrogen atoms does not affect the overall final geometry of these complexes. For this series of macrocyclic complexes, the smaller the ligand the more pronounced is the folding necessary to accommodate the metal at its centre. The structure of a complex of a 12-membered macrocycle having four donor atoms one of which approaches the metal from the apical position is reported for the first time.
    No preview · Article · Nov 1994 · Journal of the Chemical Society Dalton Transactions
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    ABSTRACT: New bridged fulvalene (Fv = μ-η5 : η5-C10)H8) binuclear molybdenum(III) and tungsten(III) compounds were obtained from the reaction of [M(η5-C5H5)2(SC6H5)2] (M = Mo or W) with dirhenium decacarbonyl. The complex [Mo2Fv(μ-SC6H5)Cp2][Re2(μ-SPh)3(CP)6] was characterized by single crystal X-ray diffraction. The cation [Mo2Fv(μ-SC6H5)Cp2]+ showed a relatively rigid [Mo2FvCp2] unit with an Mo-S-Mo angle of 83.88(7)°, M-S distances 2.442(2) and 2.450(2) Å and a Mo⋯Mo distance of 3.256(1) Å. In the [Re2(μ-SPh)3(CO)6]− anion, each metal atom has an octahedral environment (three carbonyl and three thiolate groups) with the two octahedra sharing the face containing the sulphur donor atoms (Re-S-Re angles from 86.63(8) to 86.83(8)°). The Re⋯Re distance of 3.457(1) Å is long. Extended Hückel molecular orbital calculations were done in order to understand the nature of the metal-metal interaction in the cation and some related complexes. Although the Mo⋯Mo distance is relatively long, there is a strong interaction between the two d3 metal atoms, assigned to a μ bond, which leads to diamagnetic behaviour (the anion with two d6 ReI centres is also diamagnetic).
    No preview · Article · Jul 1993 · Journal of Organometallic Chemistry
  • Maria A.A.F. de C.T. Carrondo · Vitor Félix · M.Teresa Duarte · M.Amélia Santos
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    ABSTRACT: Reaction of HgCl2, in slight excess of 1 molar equivalent of the ligand ([18]aneN6) in water, produces a colourless solution containing [Hg([18]aneN6)](HgCl4). The X-ray structure of this complex shows that the six nitrogen donor atoms of the macrocycle surround the mercury(II) atom in a distorted trigonal prismatic coordination. Cyclic voltammetry of [Hg([18]ane)]2+ shows a chemically reversible reduction at a HDM electrode, with E = −0.293 V vs S.C.E. at pH 9.37 and a scan rate of 200 mV s−1. The global oxidation-reduction process involves two electrons and two protons.
    No preview · Article · Apr 1993 · Polyhedron
  • Sílvia Chaves · Rita Delgado · M. Teresa Duarte · J. Armando L. Silva · Vitor Félix · Maria A. A. F. de C. T. Carrondo
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    ABSTRACT: A new N-diacetate derivative of an asymmetrical 14-membered oxatriaza macrocycle, 1-oxa-4,8,12-triazacyclotetradecane-4,12-diacetic acid (H2L2), has been synthesised from the parent amine by the method of complete carboxymethylation followed by anion-exchange chromatography. Its protonation constants have been determined by potentiometric and 1H NMR techniques (at 25.0 °C and I= 0.10 mol dm–3). The first two protonations occur at the nitrogen atoms, the third at a carboxylate group and not at the last nitrogen atom. The stability constants of the complexes formed by this ligand with various first-series transition metal ions, Zn2+, Cd2+, Pb2+ and Ca2+ were determined by potentiometric measurements. The value for the copper complex (and also for the nickel one) is very high while the complexes of Ca2+, Mn2+ and Pb2+ have relatively low stability. An X-ray structure determination of the complex [CuL2]·5H2O has been performed in order to understand these values. Crystals are monoclinic, space group P21/c, a= 11.19(3), b= 12.19(2), c= 16.22(6)Å, β= 110.16(9)°. The structure was refined to a final R= 0.089 for 3656 reflections with |Fo| 2σ|Fo|. The co-ordination geometry around the copper atom can be described as a distorted octahedron in which the equatorial plane is defined by the three nitrogen atoms of the ring and an oxygen atom of one of the carboxylate groups of the ligand. Two oxygen atoms occupy the axial positions, one from the remaining carboxylate group and the other from the macrocyclic ring. Hence, in the crystalline state (and probably also in solution) all the donor atoms co-ordinate to the metal ion, the ligand being in a folded, very strained conformation. The low stability of the complexes of the larger metal ions (Ca2+, Mn2+ and Pb2+) could be understood if one of the nitrogen-donor atoms of the ring were not involved in the co-ordination.
    No preview · Article · Sep 1992 · Journal of the Chemical Society Dalton Transactions
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    ABSTRACT: The structure of ammonium tetramethylammonium bis(N-hydroxy-iminodiacetate)vanadate(IV) was determined by x-ray analysis. One independent anion and two cations were found in the asymetric unit. The crystal is monoclinic, space group C2/c, with a=15.820(9), b=16.450(6), c=16.311(4) å, Β=118.92(3) deg., V=3715(3) å3, Z=8, Dx=1.56g cm-3, Μ(Mo-Ka)=5.59 cm-1, F(OOO)=2028, M=434.9 for C12H24N4O10V. The structure was solved and refined to R(F)=0.029 and Rw(F)=0.040. The complex anion does not contain the oxovanadium(IV) group, but contains vanadium(IV) as the central atom. This is the first example of a vanadium(IV) complex octacoordinated to nitrogen and oxygen atoms exhibiting a highly distorted dodecahedral geometry. The chelation is along two a and four g edges. As the angles ones are bonding distances (N-O, 1.381(3), 1.382(4) å) the angles around the central atom are very different from those usually observed in the dodecahedral complexes. The V-O distances range from 1.973(3) to 2.071(3) å and the V-N distances range from 2.002(3) to 2.003(4) å.
    No preview · Article · Apr 1992 · Structural Chemistry
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    ABSTRACT: The electrochemical behaviour of the new Nb(IV) derivatives [Nb(eta-5-C5H5)2(L-L)][PF6]2 where L-L = 2,2'-bipyridyl or o-phenanthroline and of the molybdenum(IV) and tungsten(IV) analogues was investigated and the reduction of the coordinated ligand was observed along with the redox processes based on the metal. The structure of the new [Nb(eta-5-C5H5)2(bpy)][PF6]2 (1) and of the known related compounds [Mo(eta-5-C5H5)2(o-phen)][PF6]2 (2) and [W(eta-5-C5H5)2(o-phen)][PF6]2 (3) have been characterized by single crystal X-ray diffraction studies. The Mo and the W complexes are isostructural, while the Nb complex crystallizes in a slightly different monoclinic cell. In complex 1 the Nb-N bond distances are 2.226(6) and 2.218(6) angstrom and the bond angle is 72.6(3)-degrees, while in complex 2, Mo-N bond distances are 2.193(7) and 2.186(7) angstrom and the N-Mo-N bond angle is 74.7(3)-degrees and in complex 3, W-N bond distances are 2.181(11) and 2.179(9) angstrom and the N-W-N bond angle is 74.7(4)-degrees. An extended-Huckel molecular-orbital study of the bonding of these complexes showed the absence of back donation to the low-energy, empty orbitals of the nitrogen ligand.
    No preview · Article · Mar 1992 · Journal of Organometallic Chemistry
  • Maria A.A.F. De C.T. Carrondo · M.Teresa Leal S. Duarte · J.Armando L. Silva · J.J.R.Fraústo da Silva
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    ABSTRACT: The structure of N,N′-bipyridyl, N-methoxy iminodiacetate oxovanadium(IV) has been determined by X-ray diffraction. The complex shows a distorted octahedral geometry with the vanadium atom coordinating to the oxo oxygen, two carboxyl oxygen atoms and an imino nitrogen of the N-methoxy iminodiacetate ligand, and two nitrogen atoms of the bipyridyl ligand. The VO and VN equatorial distances are 1.970(4), 1.982(4), 2.088(4) and 2.094(4) Å, respectively, while the axial VO and VN distances are 1.602(4) and 2.379(4) Å.
    No preview · Article · Dec 1991 · Polyhedron
  • Maria A. A. F. de C. T. Carrondo · M. Teresa Leal S. Duarte · Paul O'Brien · Michael B. Hursthouse
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    ABSTRACT: The structures of cis-bis(L-hydroxyprolinato) copper(II) tetrahydrate (1) and trans-bis(D-allohydroxyprolinato) copper(II)–water(2/5)(2) have been determined by X-ray analysis. These compounds provide an unusual example of epimeric amino acids supporting different geometrical arrangements in the copper(II) square plane. Crystals of complex (1) are monoclinic, space group P21, a= 10.209(6), b= 8.071(3), c= 9.698(3)Å, β= 100.33(4)°, and Z= 2. Crystals of complex (2) are orthorhombic, space group P212121, a= 8.678(5), b= 17.737(4), c= 18.686(7)Å, and Z= 8, with two molecules per asymmetric unit. Both structures were solved by Patterson and difference electron-density syntheses. Final R values of 0.037 for 2 248 reflections and 0.045 for 2 207 reflections were obtained for complexes (1) and (2) respectively. In both structures each copper atom has an essentially square-planar environment with the hydroxyproline co-ordinating by the pyrrolidine nitrogen and carboxylate oxygen. A distorted six-fold co-ordination is completed by weak Cu O interactions. The Cu–N, Cu–O bond lengths and Cu O axial distances in the two structures are within the range observed in similar complexes. Extensive systems of hydrogen bonding are present in both structures.
    No preview · Article · Jan 1990 · Journal of the Chemical Society Dalton Transactions
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    ABSTRACT: Reaction-solution calorimetric studies of the title complexes led to Ti-SC2H5, W-SC2H5, and W-SC6H5 bond enthalpies. The results support a previous view that M-SR bond strengths increase with the size of the n-alkyl chain and that M-SC6H5 bond enthalpies are higher than M-S(alkyl) bond enthalpies. The molecular structure of Ti(η5-C5H5)2(SC 2H5)2, determined by X-ray diffraction, shows a distorted tetrahedron geometry around the Ti central atom, with S-Ti-S and centroid-Ti-centroid angles of 93.8 (1) and 131.8 (4)°, respectively, and a mean Ti-S bond length of 239.3 (3) pm. Extended Hückel molecular orbital calculations show that an exo conformation of the thiolate ligands is preferred for molybdenum complexes, while an endo geometry is favored by the titanium analogues. The conformation of cyclopentadienyl rings is also discussed by using the same theoretical method. Potential energy calculations indicate that the complex Mo(η5-C5H5)2(SC 4H9t)2 is destabilized by steric effects, these being negligible in the case of Ti(η5-C5H5)2(SC 6H5)2.
    No preview · Article · Jul 1988 · Inorganic Chemistry
  • Maria J. Calhodra · Maria A.A.F. de C.T. Carrondo · M.H. Garcia · Michael B. Hursthouse
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    ABSTRACT: Crystals of [Mo(η5-C5H5)2(NH3)(SC6H5)][PF6] · (CH3)2CO solvate are monoclinic, space group P21/n, a 9.777(1), b 11.6343(2), c 19.656(4) Å, β 93.60(1)°, V 2231-46 Å3, Z  Dc 1.617 g cm−3, μ(Mo-Kα) 7.21 cm−1. The structure was solved by Patterson and difference Fourier electron density synthesis and refined to R (F)  0.047 and Rw(F)  0.057 for 3293 observed reflections. The molybdenum atom has the usual distorted tetrahedral geometry comprising the two MoCp (Cp  η5-C5H5) ring normals (MoCp 1.988(13), 1.989(15) Å), one Mo-NH3 (MoN 2.226(12) Å), and one MoSc6H5 (MoS 2.465(5) Å). Extended HMO and steric energy calculations were made in order to account for the geometry adopted by the thiolato ligand in this complex.
    No preview · Article · Mar 1988 · Journal of Organometallic Chemistry
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    ABSTRACT: The vanadium(IV) octaco-ordinated complex (NH4+)[N(CH3)4+][V(HIDA)2](HIDA =N-hydroxy-iminodiacetate), whose anion is a likely model for the natural compound ‘amavadin,’ has been prepared and its crystal and molecular structures have been determined by X-ray crystallography; this is the first example of an octaco-ordinated vanadium(IV) complex with just N and O donor atoms.
    No preview · Article · Jan 1988 · Journal of the Chemical Society Chemical Communications
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    ABSTRACT: The crystal structure of bis(L-arginine)Cu(II)(acetate)2trihydrate has been determined by X-ray analysis. The complex crystallizes in the monoclinic space group P21, with cell dimensions a = 15.948(2), b = 16.878(2), c = 10.378(2) Å, β = 108.47(1)°, Z = 4. There are two independent formula units in the asymmetric unit. The Cu atoms were located from a Patterson synthesis and the remaining atoms from difference Fourier syntheses. The structure was refined by least-squares to R = 0.079 and R = 0.11. Each copper atom has an essentially square planar coordination with the two arginine molecules chelated via the carboxy oxygens and the α-amino nitrogens, but with distorted six-fold coordinations completed by weak Cu…O (acetate) interactions. Electrostatic interactions between the acetates and the protonated ends of the amino acid residues link the two independent [Cu(L-arginine)2(acetate)2] units into dimers, which are then connected via hydrogen bonds, also involving the water molecules, into an infinite network.
    No preview · Article · May 1986 · Inorganica Chimica Acta
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    ABSTRACT: The energetics of transition-metal-sulfur bonds in bis(η5-cyclopentadienyl)bis(thiolato)metal complexes, M(η5-C5H5)2(SR)2 (M = Mo, W, Ti), has been reinvestigated and compared with reevaluated metal-oxygen data on the same type of molecules. Bond enthalpy terms, E(Mo-SR) (R = n-C3H7, i-C3H7, n-C4H9, t-C4H9, and n-C10H21), which were obtained by using calorimetric values for the standard enthalpies of formation of the complexes, confirm a strong steric effect in the case of t-C4H9S and indicate an increase in metal-sulfur bond strength with the length of the n-alkyl chain, E(Mo-SC10H21-n) ≳ E(Mo-SC4H9-n) ≳ E(Mo-SC3H7-n). The thermochemistry of the complex Mo(η5-C5H5)2(SO4) was also studied, leading to E(Mo-O) ≈ 338 ± 13 kJ mol-1. This value excludes noticeable strain on the metallacycle, since it compares with other molybdenum-oxygen bond enthalpy terms. The molecular structure of the sulfate complex, which was also determined in the present study, is compatible with the Mo-O bond enthalpy. The structural data were obtained by X-ray diffraction and show bidentate coordination of the sulfate ligand, with O-Mo-O = 66.1 (2)° and Mo-O = 211.3 (3) pm. The angle O-S-O = 98.3 (2)° (coordinated oxygen) shows a small distortion of this moiety, and extended Hückel calculations show that the rigidity of the SO4 geometry is responsible for the small O-Mo-O angle. The sulfate complex crystallizes in the orthorhombic space group Cmcm with four molecules per unit cell; the lattice constants are a = 935.6 (5) pm, b = 854.7 (2) pm, and c = 1297.9 (4) pm.
    No preview · Article · Apr 1986 · Organometallics
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    ABSTRACT: The crystal structure of bis(L-lysine)Cu(II) chloride dihydrate has been determined by X-ray analysis. The complex crystallizes in the monoclinic space group P21, with cell dimensions a = 5.189(1), b = 16.988(3), c = 11.482(2) Å, β = 93.57(1)°. The position of the Cu atom was found from a Patterson synthesis, the remaining atoms were located with DIRDIF. The structure was refined by least-squares to R = 0.060 and Rw = 0.065 for 2637 observed reflections. The copper(II) atom has an essentially square planar coordination with the two lysine molecules chelated via the carboxy oxygen and the α-amino nitrogen. However the two chlorine atoms form weak interactions with the metal to complete a strongly tetragonally elongated six-fold coordination. The two aliphatic chains have rather different geometries and are extended in a zig-zag mode. Extensive hydrogen bonding links the complex and the water molecules together.
    No preview · Article · Sep 1985 · Inorganica Chimica Acta
  • Maria A.A.F. De C.T. Carrondo · Angela M.T.S. Domingos · G.A. Jeffrey
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    ABSTRACT: Crystals of trans-{ReCl[CN(t-C4H9)](Ph2PCH2CH2PPh2)2} · C4H8O solvate are monoclinic, space group P21/n, a 24.098(7), b 16.558(5), c 13.402(4) Å, β 90.97(3)°, V 5346.82 Å3 at 25°C. F(000)= 2392, Z = 4, λ(Cu-Kα 1.5418 Å, μ(Cu-Kα) 57.99 cm−1Dc 1.46 g cm−3. The structure was solved by Patterson and difference Fourier electron density syntheses and refined to R (F)= 0.048 and Rw(F)= 0.067 for 4763 observed reflections. The Re atom is in a distorted octahedral coordination with the chloride and the isocyanide as axial ligands and the two dppe groups as equatorial ligands. The ReC bond length is 1.926(9) Å and the ClReC bond angle is 175.5(2)°. The CNBut ligand is nearly linear with a 174.0(9)° angle at the N and a CN bond length of 1.154(10) Å. The t-Bu group and the solvate molecules are disordered.
    No preview · Article · Jul 1985 · Journal of Organometallic Chemistry