Showing papers on "Tetrahedral molecular geometry published in 1989"

Characterization of the inhibitor complexes of cobalt carboxypeptidase A by electron paramagnetic resonance spectroscopy.

Abstract: The metal coordination sphere of cobalt-substituted carboxypeptidase A and its complexes with inhibitors has been characterized by X-band electron paramagnetic resonance (EPR) spectroscopy. The temperature dependence of the EPR spectrum of cobalt carboxypeptidase and the g anisotropy are consistent with a distorted tetrahedral geometry for the cobalt ion. Complexes with L-phenylalanine, a competitive inhibitor of peptide hydrolysis, as well as other hydrophobic L-amino acids all exhibit very similar EPR spectra described by three g values that differ only slightly from that of the cobalt enzyme alone. In contrast, the EPR spectra observed for the cobalt enzyme complexes with 2-(mercaptoacetyl)-D-Phe, L-benzylsuccinate, and L-beta-phenyllactate all indicate an approximately axial symmetry of the cobalt atom in a moderately distorted tetrahedral metal environment. Phenylacetate, beta-phenylpropionate, and indole-3-acetate, which exhibit mixed modes of inhibition, yield EPR spectra indicative of multiple binding modes. The EPR spectrum of the putative 2:1 inhibitor to enzyme complex is more perturbed than that of the 1:1 complex. For beta-phenylpropionate, partially resolved hyperfine coupling (122 x 10(-4) cm-1) is observed on the g = 5.99 resonance, possibly indicating a stronger metal interaction for this binding mode. The structural basis for the observed EPR spectral perturbations is discussed with reference to the existing crystallographic kinetic and electronic absorption, nuclear magnetic resonance, and magnetic circular dichroic data.

Metal Complexes with Macrocyclic Ligands Part XXX†. Synthesis and structure of halocuprates of tetraprotonated 1,4,8,11-tetraazacyclotetradecane and its Cu2+ complex

Abstract: By mixing acidic solutions of 1,4,8,11-tetraazacyclotetradecane (Cy) with CuX2 (X = Cl−, Br−), either the hexahalocuprates of the tetraprotonated form of the macrocycle ([CyH4] [CuX6]) or the tetrahalocuprates of its Cu2+ complex ([CuCy] [CuX4]) are obtained. The structures of the chloro derivatives are established by X-ray diffraction analysis. In [CyH4] [CuCl6], the Cu2+ is in a tetragonally distorted octahedral geometry with four short and two long CuCl bonds. The tetraprotonated macrocycle is centrosymmetric, and its conformation is exodentate, so that the four ammonium groups are as far as possible from each other to minimize the electrostatic repulsion. In [CuCy] [CuCl4], the Cu2+ ion complexed by the macrocycle is surrounded by four N-atoms in a square-planar arrangement. In addition, the axial positions are occupied by two Cl− ions of two CuCl units, which act as bridges. The macrocycle is in the trans-III-configuration. The other Cu2+ ion is coordinated by four Cl− ions in a distorted tetrahedral geometry. IR and VIS spectra of the chloro and bromo derivatives are used to discuss the structure of the bromo species.

Structure of copper(II) perchlorate hexahydrate.

Abstract: Cu(ClO4)2.6H2O, Mr = 370.54, monoclinic, P2(1)/c, a = 5.137 (1), b = 22.991 (3), c = 13.849 (2) A, beta = 90.66 (1) degree, V = 1635.4 (4) A3, Z = 6, Dx = 2.26 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 26.44 cm-1, T = 296 K, F(000) = 1122, 2911 unique reflections having I greater than sigma 1, R = 0.030. Each of the two inequivalent copper ions is coordinated by six water-molecule O atoms in a significantly distorted octahedral arrangement. Each of the three inequivalent but geometrically quite similar perchlorate groups is slightly distorted from regular tetrahedral geometry. The overall observed mean Cl-O distance is 1.429 (5) A while the overall observed mean perchlorate O-O distance is 2.333 (8) A. Both the Cu-O complexes and the perchlorate ions were tested and found to behave as rigid bodies. The perchlorate-ion parameters corrected for rigid-body motion are: overall mean Cl-O distance, 1.453 (6) A; overall mean perchlorate O-O distance, 2.372 (8) A. Location and refinement of the 18 H atoms gave a detailed account of hydrogen bonding, which occurs between oxygen octahedra, between oxygen octahedra and perchlorate groups, and, more weakly, within oxygen octahedra.

Synthesis, X-ray crystal structure, and electronic structure of a trinuclear WCu2 cluster containing a hexathiolato tungsten(IV) core

Abstract: In the new compound (PPh3)Cu(µ-Sptol)3W(µ-Sptol)3Cu(PPh3), (ptol = 4-methylphenyl, p-tolyl), the tungsten is homoleptically ligated by six thiolate ligands, and co-ordinates to two copper(I) atoms in a biconfacial octahedral/tetrahedral geometry; density functional calculations of an idealized model show that the major component of the bonding is transfer of charge from S to Cu, with a smaller contribution from a metal–metal bonding interaction.

1,4-Benzodiazepines as ligands. Synthesis, characterization and crystal and molecular structure ofbis(8-chloro-6-(o-chlorophenyl)-1-methyl-4H-s-triazolo[4,3-a]1,4-benzodiazepine (triazolam)) cadmium (II) dichloride

Abstract: The compound C34H24CdN8Cl6 was prepared and characterized by means of X-ray, IR, and Raman measurements. The crystals are monoclinic, space groupC2/c, (No. 14) witha=22.284(3),b=14.501(2),c=14.595(2) Aβ=129.77(1)° andZ=4. The structure was solved by the heavy-atom method, and least-squares refinement of structural parameters led to a conventionalR factor of 0.040 for 2379 independent reflections. The structure consists of discrete molecules, in which the Cd atom is coordinated in a distorted tetrahedral geometry by two chlorine atoms and by two nitrogens of two triazolic rings of triazolam molecules. Infrared and Raman bands are assigned on the basis of the known structure. An electronic charge calculation has been performed on the unbonded ligand.

Studies on Benzothiazoline Complexes of Manganese(II)

Abstract: The 1:1 and 1:2 molar reactions between hydrated manganese acetate and the benzothiazolines having the donor group NS have yielded tetra-coordinated manganese(II) Schiff base complexes. The resulting complexes [Mn(Bzt) (CH3COO)H2O] and [Mn(Bzt)2] (where BztH = monofunctional bidentate benzothiazoline) have been characterized on the basis of elemental analysis, molecular weight determinations and conductance and magnetic measurements. The infrared, electronic and electron spin resonance spectral studies indicate a high spin tetrahedral geometry for the resulting complexes. Some of these derivatives have also been screened for their fungicidal activity.

Are tetrahedral intermediates formed by addition of nucleophiles to organoboranes in the gas phase

Abstract: Nucleophilic addition of CD3O– to Me2BOMe gives the same addition product as the corresponding reaction between Me2BOCD3 and MeO–, as evidenced by the identical collisional activation mass spectra of the products. This is interpreted in terms of exclusive formation of a boron product ion of tetrahedral geometry. The decompositions of the product involve loss of MeOH and CD3OH and the formation of MeO– and CD3O–. The major decompositions of (CD3)3B +–OCH2CH2XMe (X = O, S, or NMe2) are similar to those outlined above and may be explained by initial formation of (CD3)3 OCH2CH2XMe. However, there are some unusual fragmentations (e.g. loss of CH3D) which may occur through the alternative structure (CD3)3[graphic omitted](Me)CH2CH2O–. It is suggested that other ambident species may also react with Me3B to form several tetrahedral species, e.g. deprotonated methyl acetate could yield Me3CH2CO2Me, Me3OC(OMe)CH2, and Me3—[graphic omitted](Me)[graphic omitted]. The formation of the third structure is supported by the pronounced loss of ketene from this system.

Cyclic (ALN)n Compounds as Precursors to Aluminum Nitride: Synthesis and Structure of [(CH3)2AlNH2]3 and the Planar Species [(t-C4H9)2AlNH2]3

Abstract: The crystal and molecular structures of the title compounds, [(CH3)2AlNH2]3 1 and [(t-C4H9)2AlNH2]3 2, have been determined in connection with their investigation as possible precursors to aluminum nitride. Both compounds have an (AlN)3 ring-structure with distorted tetrahedral geometries for the ring Al and N atoms. The distortion from tetrahedral geometry is most pronounced for the N atoms where the endocyclic Al-N-Al bond angles average 125.3 for 1 and 134.2 for 2. The (AlN)3 ring in 1 is in a skew-boat conformation with no unusual intra- or intermolecular contacts. Compound 2 on the other hand exhibits an unprecedented planar (AlN)3 ring as required by a crystallographic three-fold symmetry axis. The effects of the Al and N substituents on the (AlN)3 ring size and conformation, as well as on the endocyclic Al-N-Al bond angles, are discussed in the context of the structural results obtained for these and other (AlN)n ring compounds.

Electron spin resonance and optical studies of doped copper (II) Tetrahedral complexes

Abstract: This report presents an investigation of a pseudotetrahedral bromocuprate (II) compound. The bromocuprates exhibit a great structural diversity, however, the comparatively rare compressed tetrahedral compounds have been somewhat neglected. The determination of the electronic and geometric structure of these compounds has implications in the analysis of active sites in copper blue proteins. Electron Spin Resonance (E.S.R.) and optical spectra have been measured at low temperature, for single crystals of copper (II) doped into bis( ethylenediammoniummonobromide) tetrabromozincate (II), ( enH.HBr)2 ZnBr4. The room temperature powder reflectance spectrum has also been measured for this compound, along with that of the pure zinc analogue. The transition energies derived from the electronic spectra have been assigned and compared to the respective transitions based on previous studies. With the aid of a computer program, a set of theoretical transition energies has been calculated utilizing the Angular Overlap Model. Adjusting these to fit the observed values confirms the presence of a distorted tetrahedral geometry for the guest ion. At 77K, the E.S.R. spectrum of (enH2)2Zn[Cu]Br6 exhibits well resolved copper hyperfine and bromine superhyperfine couplings. Computer simulation techniques have produced optimum values for these parameters, which suggest that the principal z-axis of the superhyperfine tensor does not coincide with the copper-bromine bond direction. The bonding in the guest [CuBr4]2- ion has been described in terms of the relative unpaired electron density within the bromine 4s and 4p orbitals, which shows an increased covalency when compared with the chlorine counterpart. A highly rhombic g tensor results in an unusual groundstate. The calculated mixing coefficients and corresponding wavefunction parameters show that the dz2 orbital makes a small but significant contribution by mixing with the pure dx2-y2 orbital.

Structure of Copper(II) Perchlorate Hexahydrate.

Abstract: Cu(ClO4)2.6H2O, Mr = 370.54, monoclinic, P2(1)/c, a = 5.137 (1), b = 22.991 (3), c = 13.849 (2) A, beta = 90.66 (1) degree, V = 1635.4 (4) A3, Z = 6, Dx = 2.26 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 26.44 cm-1, T = 296 K, F(000) = 1122, 2911 unique reflections having I greater than sigma 1, R = 0.030. Each of the two inequivalent copper ions is coordinated by six water-molecule O atoms in a significantly distorted octahedral arrangement. Each of the three inequivalent but geometrically quite similar perchlorate groups is slightly distorted from regular tetrahedral geometry. The overall observed mean Cl-O distance is 1.429 (5) A while the overall observed mean perchlorate O-O distance is 2.333 (8) A. Both the Cu-O complexes and the perchlorate ions were tested and found to behave as rigid bodies. The perchlorate-ion parameters corrected for rigid-body motion are: overall mean Cl-O distance, 1.453 (6) A; overall mean perchlorate O-O distance, 2.372 (8) A. Location and refinement of the 18 H atoms gave a detailed account of hydrogen bonding, which occurs between oxygen octahedra, between oxygen octahedra and perchlorate groups, and, more weakly, within oxygen octahedra.