Showing papers on "Tetrahedral molecular geometry published in 2012"

Stepwise intramolecular photoisomerization of NHC-chelate dimesitylboron compounds with C-C bond formation and C-H bond insertion.

Abstract: C,C-chelate dimesitylboron (BMes2) compounds containing an N-heterocyclic carbene (NHC) donor have been obtained. Single-crystal X-ray diffraction analyses established that the boron atom in these compounds is bound by four carbon atoms in a distorted tetrahedral geometry. Compared to previously reported N,C-chelate dimesitylboron compounds, the new C,C-chelate boron compounds have a much larger HOMO–LUMO energy gap (>3.60 eV). They do, however, respond to UV irradiation (300 nm) in the same manner as N,C-chelate BMes2 compounds do, undergoing photoisomerization and converting to an intensely colored (yellow or orange) isomer A quantitatively, with a high quantum efficiency (0.60–0.75). NMR and single-crystal X-ray diffraction analyses established that the structure of A is similar to the dark isomers obtained from N,C-chelate BMes2 compounds. However, unlike the N,C-chelate dark isomers that have the tendency to thermally reverse back to the light colored isomers, the isomers A of the C,C-chelate BMes2 a...

Cooperative Metal–Ligand-Induced Properties of Heteroleptic Copper(I) Xanthate/Dithiocarbamate PPh3 Complexes

Abstract: Four new heteroleptic mononuclear complexes, [Cu(PPh3)2L1](1) {L1 = (C9H11O2CS2), [2-(4-methoxyphenyl)ethyl]xanthate}, [Cu(PPh3)2L2] (2) [L2 = (C6H7OCS2), benzylxanthate], [Cu(PPh3)2L3] (3) [L3 = (C5H9OCS2), (cyclobutylmethyl)xanthate] and [Cu(PPh3)2L4] (4) [L4 = (NC13H13NCS2), N-benzyl-N-(4-pyridylmethyl)dithiocarbamate], have been synthesized and characterized by using microanalysis, IR, UV/Vis, 1H, 13C and 31P NMR spectroscopy and X-ray crystallography; their photoluminescent behaviour and molecular electrical conductivity have been investigated. CuI possesses four-coordinate distorted tetrahedral geometry in all the complexes. All are weakly conducting and exhibit semiconductor behaviour in the studied 303363 K temperature range. Complex 4 shows striking luminescent behaviour emitting bluish green light at 480 nm in CH2Cl2 solution at room temperature

The influence of the Jahn-Teller effect at Fe2+ on the structure of chromite at high pressure

Abstract: The crystal structure of chromite FeCr2O4 was investigated to 13.7 GPa and ambient temperature with single-crystal X-ray diffraction techniques. The unit-cell parameter decreases continuously from 8.3832 (5) to 8.2398 (11) A up to 11.8 GPa. A fit to the Birch–Murnaghan equation of state (EoS) based on the P–V data gives: K 0 = 209 (13) GPa, K′ = 4.0 (fixed), and V 0 = 588 (1) A3. The FeO4 tetrahedra and CrO6 octahedra are compressed isotropically with pressure with their Fe–O and Cr–O bond distances decreasing from 1.996 (6) to 1.949 (7) A and from 1.997 (3) to 1.969 (7) A, respectively. The tetrahedral site occupied by the Fe2+ cation is more compressible than the octahedral site occupied by the Cr3+ cation. The resulting EoS parameters for the tetrahedral and the octahedral sites are K 0 = 147 (9) GPa, K′ = 4.0 (fixed), V 0 = 4.07 (1) A3 and K 0 = 275 (24) GPa, K′ = 4.0 (fixed), V 0 = 10.42 (2) A3, respectively. A discontinuous volume change is observed between 11.8 and 12.6 GPa. This change indicates a phase transition from a cubic (space group Fd- $${\overline{3}}$$ m) to a tetragonal structure (space group I41 /amd). At the phase transition boundary, the two Cr–O bonds parallel to the c-axis shorten from 1.969 (7) to 1.922 (17) A and the other four Cr–O bonds parallel to the ab plane elongate from 1.969 (7) to 1.987 (9) A. This anisotropic deformation of the octahedra leads to tetragonal compression of the unit cell along the c-axis. The angular distortion in the octahedron decreases continuously up to 13.7 GPa, whereas the distortion in the tetrahedron rises dramatically after the phase transition. At the pressure of the phase transition, the tetrahedral bond angles along the c-axis direction of the unit cell begin decreasing from 109.5° to 106.6 (7)°, which generates a “stretched” tetrahedral geometry. It is proposed that the Jahn–Teller effect at the tetrahedrally coordinated Fe2+ cation becomes active with compression and gives rise to the tetrahedral angular distortion, which in turn induces the cubic-to-tetragonal transition. A qualitative molecular orbital model is proposed to explain the origin and nature of the Jahn–Teller effect observed in this structure and its role in the pressure-induced phase transition.

Au102+: A Tetrahedral Cluster Exhibiting Spherical Aromaticity

Abstract: We propose that the global minimum structure of the Au102+ system has a highly symmetrical tetrahedral geometry and is clearly separated from the other isomers by a high relative energy gap. The large highest occupied molecular orbital-to-lowest unoccupied molecular orbital (HOMO–LUMO) gap as well as the superatom and spherical aromatic characters account for the high stability of this Td Au102+ geometry.

Synthesis, characterization, and biological activities of zinc, cadmium, copper, and nickel complexes containing meta -aminophenyl benzimidazole

Abstract: ZnX2, CdX2, CuX2, and NiX2 (X = Cl−, Br−, , or ) react with meta-aminophenyl benzimidazole in 1 : 2 mole ratio at reflux in methanol to give Zn2Cl4L3 · 2H2O, ZnBr2L2(OH2), [Zn(OClO3)L3]ClO4 · 3H2O, CdCl2L(OH2), Cd2Br4L3 · 2H2O, Cd(ONO2)2L2 · 2H2O, [Cu2Cl4L3] · 2H2O, Cu2Br4L3, [Cu(OClO3)L2]2(ClO4)2, [NiCl2L(OH2)] · 2H2O, [NiBrL3]Br · 3H2O, and [Ni(OClO3)L3]ClO4 · H2O. These complexes were characterized by elemental analysis, melting point, TGA, conductivity, magnetic moment measurements, IR, far-IR, NMR, electronic, and mass spectral studies. Based on these studies, Zn2Cl4L3 · 2H2O and Cd2Br4L3 · 2H2O were assigned binuclear structures while [Zn(OClO3)L3]ClO4 · 3H2O, CdCl2L(OH2), Cd(ONO2)2L2 · 2H2O, [NiCl2L(OH2)] · 2H2O, and [NiBrL3]Br · 3H2O were mononuclear with tetrahedral geometry. The copper complexes were binuclear and exhibit strong antiferromagnetic coupling at room temperature. Square pyramidal geometry was proposed for halo complexes of copper and ZnBr2L2(OH2) and square-planar geometry for perch...

Aluminepin: Aluminum Analogues of Borepin and Gallepin

Abstract: We report synthesis of dibenzoaluminepin as the first aluminepin, an aluminum analogue of borepin and gallepin. This compound contains one molecule of ethereal solvent on the Al atom, which adopts a tetrahedral geometry. The central 7-membered aluminepin ring has a boatlike conformation and was characterized by single-crystal X-ray diffraction, (1)H/(13)C NMR, and DFT studies. In addition, NICS, NBO, and theoretical calculations provide insight into the nature of the bonding and aromaticity of aluminepins.

Transition metal complexes with ligand containing thioamide moiety: synthesis, characterization and antibacterial activities

Abstract: A new series of transition metal complexes of Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) with the ligand 3-thionicotinoylaminodibenzofuran (L) were synthesized. The complexes were characterized by elemental analyses, metal content, spectroscopic methods (IR, UV-vis, NMR and EPR), conductivity and susceptibility measurements and by thermal studies. A quantum-mechanical interpretation of the electronic transitions for the free and coordinated ligand in the Ni(II) complex was performed using EHT-MO approach in order to get more information about the atoms involved in coordination to the metallic ion. According to all this information, we propose an octahedral geometry for Fe(II) and Co(II) complexes, a square-planar geometry for Ni(II) and Cu(II) complexes and a tetrahedral geometry for Zn(II) complex. The antibacterial activity of the ligand and its complexes was studied against selected bacteria Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. It was found that all the complexes are antimicrobially active and show higher activity than the free ligand.

XAFS investigations of copper(II) complexes with tetradentate Schiff base ligands

Abstract: X-ray absorption fine structure spectra have been investigated at the K-edge of copper in copper(II) salen/salophen complexes: [Cu(salen)] (1), [Cu(salen)CuCl2].H2O (2), [Cu(salophen)] (3) and [Cu(salophen) CuCl2].H2O (4), where salen2− = N,N′-ethylenebis (salicylidenaminato); salophen2− = o-phenylenediaminebis(salicylidenaminato). Complexes 1 and 3 are supposed to have one type of copper centers (called (Cu1)) and complexes 2 and 4 two types of copper centers (called (Cu1) and (Cu2)) having different coordination environments and geometries. A theoretical model has been generated using the available crystallographic data of complex 1 and it has been used for analysis of the extended X-ray absorption fine structure (EXAFS) data of the four complexes to obtain the structural parameters for (Cu1) center. For this center, the obtained Cu–Cu distance (3.2 A) verifies the binuclear nature of all the complexes. For determining the coordination geometry around (Cu2) center in 2 and 4, a theoretical model has been generated using the crystal structure of a Cu(II) complex, [Cu(C16H12N2O2Cl2)]. This theoretical model has been fitted to the EXAFS data of 2 and 4 to obtain the structural parameters for (Cu2) center. The present analysis shows that (Cu1) center has square pyramidal geometry involving 2N and 3O donor atoms, whereas (Cu2) center has distorted tetrahedral geometry with 2O and 2Cl donor atoms. The values of the chemical shifts and presence of typical Cu(II) X-ray absorption near-edge spectroscopy features suggest that copper is in the +2 oxidation state in all these complexes. The intensity of ls 3d pre-edge feature has been used to investigate the geometry and binuclear nature of the complexes. Copyright © 2012 John Wiley & Sons, Ltd.

Synthesis and Crystal Structures of Cadmium Iodide Complexes of N,N ′-Diethylthiourea and 1,3-Diazinane-2-thione

Abstract: Two cadmium(II) iodide complexes, [Cd(Detu)2I2] (1) and [Cd(Diaz)2I2] (2) (Detu = N,N′-diethylthiourea; Diaz = 1,3-diazinane-2-thione) have been prepared and their structures been determined by X-ray crystallography. The crystal structures show that both complexes are mononuclear with the cadmium atom coordinated to two iodide ions and two thione ligands adopting a distorted tetrahedral geometry. Whereas, 2 exists as discrete monomeric species, the structure of 1 consists of three crystallographically independent molecules. The complexes were also characterized by IR and NMR (1H and 13C) spectroscopy. The crystal structures of [Cd(Detu)2I2] (1) and [Cd(Diaz)2I2] (2) show that the complexes are mononuclear with the cadmium atom coordinated to two iodide ions and two thione ligands adopting a distorted tetrahedral geometry. Whereas, 2 exists as discrete monomeric species, the structure of 1 consists of three crystallographically independent molecules.

High-Resolution Spectroscopy and Structure of Osmium Tetroxide. A Benchmark Study on 192OsO4

Abstract: Osmium tetroxide (OsO4) is a heavy tetrahedral molecule that constitutes a benchmark for quantum chemistry calculations. Its favorable spin statistics (due to the zero nuclear spin of oxygen atoms) is such that only A1 and A2 (Td symmetry) rovibrational levels are allowed, leading to a dense but quite easily resolvable spectrum. We reinvestigate here the ν1/ν3 stretching fundamental (940–980 cm–1) dyad region and perform new assignments and effective Hamiltonian parameter fits for the main isotopologue (192OsO4). We also investigate the ν2/ν4 bending fundamental dyad (300–360 cm–1) for the first time and perform a preliminary analysis. New experimental data have been obtained at 0.001 cm–1 resolution using an isotopically pure 192OsO4 sample and the Synchrotron SOLEIL light source. Assignments and analyses were performed using SPVIEW and XTDS software, respectively. We provide precise effective Hamiltonian parameters, including the band centers for all of the fundamental levels and rotational constants fo...

Synthesis, Characterization, and In Vitro Cytotoxicity of Triorganotin 3,5-Di-tert-butyl-4-hydroxybenzoates

Abstract: The triorganotin 3,5-di-tert-butyl-4-hydroxybenzoates, 3,5-(t-Bu)2-4-HO-C6H2COOSnR3 (R = c-C6H11, 1; C6H5, 2; C6H5CH2, 3; C6H5C(CH3)2CH2, 4), have been synthesized and characterized by elemental analysis, IR, and 1H and 13C NMR spectra. The crystal structures of 1 and 4 have been determined by X-ray single crystal diffraction and show that the tin atom possesses a distorted tetrahedral geometry. Intermolecular O−H···O hydrogen bond in 1 connects neighboring molecules into a cyclic tetramer. The in vitro cytotoxicity of the compounds against the human tumor cell lines A549 was found to be higher than that of cis-platin used clinically.

Synthesis, spectral characterization and X-ray crystal structure of biologically active organotin(IV) 3-[(3′,5′-dimethylphenylamido)]propanoates

Abstract: A new ligand was prepared by reacting 3,5-dimethylaniline with succinic anhydride in glacial acetic acid at room temperature. A series of organotin(IV) carboxylates were prepared by reacting the ligand with R2SnCl2/R3SnCl (R = Me, Bu, Ph, Oct) in 1:2/1:1 molar ratio. The synthesized complexes were characterized by elemental analyses, FT-IR, multinuclear magnetic resonance (1H and 13C) and mass spectrometry. The structures of the ligand (HL) and complex (5) were determined by single crystal X-ray diffraction analysis. FT-IR data shows that the coordination takes place through both carboxylate oxygen atoms. NMR data confirm the tetrahedral geometry in solution. In the crystal structure of ligand (HL), centrosymmetrically related molecules are linked into dimers by N–H…O hydrogen bonding interactions, while in complex (5) coordination around the tin atom is trigonal bipyramidal, with the carbon atoms of the methyl groups occupying the equatorial plane and the O atoms of symmetry-related ligands at the apices. Organotin(IV) complexes were also screened for their antibacterial and antifungal activities, and the results suggested that the synthesized complexes are better antimicrobial agents as compared to the free ligand.

Bis(Tetramethylselenophosphoramidoyl) Methylamine Complexes of Cd(Ii) and Zn(Ii): Synthesis and Multinuclear (31P, 77Se, and 113Cd) Nmr Characterization in Solution

Abstract: Five new complexes ZnL2(ClO4)2 (1), CdL2(ClO4)2 (2), CdL2(BF4)2 (3), CdLCl2 (4), and CdL(NO3)2 (5) [L = ((Me2N)2PSe)2NMe] have been synthesized and characterized by elemental analysis, infrared (IR) and multinuclear (31P, 77Se, and 113Cd), and nuclear magnetic resonance (NMR) spectroscopy. The 31P and 77Se NMR data showed that the title ligand is coordinated in a bidentate fashion to the metal center via its both P=Se groups. The solution structure of the cadmium complexes was further confirmed by its 113Cd NMR spectra, which displayed a quintuplet for the perchlorate complex and a triplet for each of the nitrate and chloride complexes, respectively due to coupling with four (two ligands) and two (one ligand) equivalent phosphorus nuclei, consistent with a four-coordinate tetrahedral geometry for the cadmium center. The results are discussed and compared with the corresponding oxo and thio analogues.

Electromechanical switching behavior of individual molecular complexes of Cu and Ni on NaCl-covered Cu(111) and Ag(111)

Abstract: In a combined scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM) study, we characterize the reversible switching between two stable states of an organometallic complex, namely, bis-dibenzoylmethanato-copper [Cu(dbm)2] adsorbed on an insulating thin film. The switching is due to the transfer of an electron between the STM tip and the molecule, accompanied by a conformational change, i.e., a transition from a square-planar to a tetrahedral geometry. Evidence is given by STM topography and spectroscopy and nc-AFM electrostatic force measurements. Similar experiments conducted on bisdibenzoylmethanato-nickel [Ni(dbm)2] show that this complex does not switch under comparable experimental conditions. We discuss these findings within the framework of crystal-field theory, stating that the occupation of the d orbitals determines the favored coordination geometry of a complex. Accordingly, only the copper complex can undergo a conformational change that facilitates stable storing of the additional electron.

Theoretical Studies of ESR Parameters and Local Lattice Structure of the Vanadate-Lithium-Borate Glasses

Abstract: Electron spin resonance spectral parameters of V4+ ions in vanadate-lithium-borate glasses have been calculated by the crystal-field theory. The theoretical results are g(parallel to) = 1.940, g(perpendicular to) = 1.983 and A(parallel to) = -175 x 10(-4) cm(-1), A perpendicular to = -65 x 10(-4) cm(-1) which are good agreement with the experimental values (g(parallel to) = 1.939(3), g(perpendicular to) = 1.998(3) and A(parallel to) = (170.6-176.4) x 10(-4) cm(-1), A(perpendicular to) = (61.3-71.4) x 10(-4) cm(-1)). In addition, the bond lengths of the local lattice structure are, respectively, R-parallel to = 1.5 angstrom and R-perpendicular to = 1.95 angstrom which have been shown to have a compressed tetrahedral geometry along the C-4 axis.

Synthesis of [MoS4](2-)-M (M=Cu and Cd) Clusters: Potential NMR Spectroscopic Structural Probes for the Orange Protein

Abstract: Two synthetic strategies of tetrathiomolybdate-metal clusters with the potential to be used as NMR structural probes for the location of the metal cofactor in the orange protein (ORP) are described. The first strategy is based on the substitution reaction in which small organic ligands bind directly to the metal centre in a molybdenum–copper hetero-dinuclear cluster. Interaction between [PPh4]2[MoS4CuCl] and either aliphatic [β-mercaptoethanol (b-me)] or aromatic [o-aminobenzenethiol (abt)] thiols in the presence of a strong base resulted in the formation of [Ph4P]2[S2MoS2Cu(b-me)] (1a) and [Et4N]2[S2MoS2Cu(abt)]·H2O·0.25DMF (1b), which can be used to obtain intermolecular NOEs. The compound 1a readily hydrolyzed to [Ph4P]2[OSMoS2Cu(b-me)] (1ahydro) in contact with a protic solvent. The second strategy consisted of the incorporation of cadmium into tetrathiomolybdate ([MoS4]2–), which gives rise to the trinuclear cluster compound [PPh4]2[(MoS4)2Cd] (2). All clusters were characterized spectroscopically and their structure determined by X-ray diffraction. The NMR spectroscopic data are consistent with the formation of a complex with a 1:1 ratio of {MoS4Cu} and thiol. The 113Cd NMR chemical shift of compound 2 is consistent with the cadmium having a tetrahedral geometry and coordinated by four sulfur ligands. The tetraphenylphosphonium cation in compound 1a was replaced by a tetramethylammonium countercation originating in the water-soluble compound [Me4N-1a]. Solubility in aqueous buffers is a requirement for incorporating this cluster into apo-ORP. These compounds will be used to identify the exact location of the ORP heterometallic cluster using NMR methodologies.

Acetate Bridged Trinuclear Zn, Ca and Mg Metal Complexes with 2- and 4-Substituted Pyridines

Abstract: The structures of the complexes [Zn2(C5H6N2)2(C2H3O2)6Ca], compound 1; [Zn(C7H10N2)2Cl2] compound 2; and [Zn2(C5H6N2)2(C2H3O2)6Mg] compound 3 were established by spectral and X-ray diffraction studies. These complexes form part of the project of design and synthesis of new alkaline-earth metal complexes with multiple applications in the fields of catalysis, material science and biochemistry. Compound 1 crystallizes in the monoclinic space group P21/c with unit cell parameters a = 11.6918(11), b = 8.2850(8), c = 15.3472(15) A, β = 96.4140(10)°, Z = 2. Compound 2 crystallizes in the orthorhombic space group Pccn with unit cell parameters a = 13.6485(13), b = 14.2962(14), c = 18.2459(18) A, Z = 8. Compound 3 crystallizes in the monoclinic space group P21/c with unit cell parameters a = 7.5531(8), b = 22.905(3), c = 8.7137(9) A, Z = 2. All three structures (1–3) were solved by direct methods and refined to R = 0.0257, 0.0346 and 0.0244, respectively. For compound 1 crystallizes with the Ca2+ ion coincident with crystallographic centre of symmetry forming a dimer. The Ca2+ ion is six-fold coordinated by three acetate ligands. The Ca polyhedron may be described as a distorted tricapped trigonal prism. The Zn2+ ion is four-fold coordinated by three O atoms from three acetate groups (atoms O2, O4 and O5) and an N atom from the 2-aminopyridine moiety. The Zn polyhedral may be described as a distorted tetrahedral coordination. Compound 2 crystallizes as a crystallographic C2-symmetric complex, in which each Zn2+ ion is bound to two 4-dimethylaminopyridine units, and two Cl−1 ions. The tetracoordinated Zn atoms adopt a distorted tetrahedral geometry. Compound 3 crystallizes with the Mg2+ ion coincident with crystallographic centre of symmetry forming a dimer. The Mg2+ ion is octahedrally coordinated by six O atoms from three acetate groups. The Zn2+ ions are in a tetrahedral geometry. In the crystal structures 1 and 3, the molecules are stabilized by N–H······O; C–H······O interactions. However in the crystal structure 2, the molecules are stabilized by C–H·····Cl interactions. The crystal structures of three new acetate bridged trinuclear metal complexes with 2- and 4-substituted aminopyridines and their conformation were obtained by X-ray diffraction techniques from suitable single crystals. These complexes form part of the project for design and synthesis of new alkaline-earth metal complexes with multiple applications in the fields of catalysis, material science and biochemistry.

Coordination compounds of n-phthaloylglycine and n-phthaloyltyrosine and their antimicrobial activities

Abstract: A B ST R A C T Coordination compounds derived from N-phthaloylglycine and N-phthaloyltyrosine were synthesized. The ligands were formed by 1:2 molar condensation of phthalic anhydride with tyrosine and glycine respectively. The complexes were formulated as [Zn(PHG) 2 (H 2O) 2] (OAc) 2[1], [Ni(PHG) 2 (H 2O) 2] (OAc) 2 [2] and [Cu(PHT) 2 ] (OAc) 2 [3] characterized by melting point, conductivity, AAS , IR, Uv-Visible spectroscopies. Both ligands were found to be bidentate. For complexes [1] and [2] the metal ions coordinate through both oxygen of OH and C=O in the carboxylic group to give octahedral geometry whereas in the [3] the coordination of metal ion occurs through both oxygen of phenoxyl and carbonyl group resulting in tetrahedral geometry. The antimicrobial studies using four test organisms( P.aerugenosa, E.Coli, S. aureus and C. albicans ) revealed that the metal complexes exhibit higher activity than their respective ligands.