Showing papers on "Tetrahedral molecular geometry published in 2005"

Organoboron compounds with an 8-hydroxyquinolato chelate and its derivatives: substituent effects on structures and luminescence.

Abstract: Four new luminescent organoboron complexes have been synthesized and fully characterized. These compounds are four-coordinate boron chelated by either 8-hydroxyquinolato (q) or functionalized 8-hydroxylquinolato ligands, including BPh2(5-(1-naphthyl)-q) (1), BPh2(5-(2-benzothienyl)-q) (2), B(2-benzothienyl)2q (3), and B(2-benzothienyl)2(2-Me-q) (4). All four compounds have a tetrahedral geometry as established by X-ray diffraction analyses. In solution, compounds 1-4 have an emission maximum at 534, 565, 501, and 496 nm, respectively, at room temperature. They emit similar colors in the solid states without red shifts of the emission band due to the lack of significant intermolecular interactions in the crystal lattices. The substituent group at C5 or C2 position of the 8-hydroxyquinolato ligand has been observed to have a significant impact on the emission energy and the emission quantum efficiency of the boron complexes. Molecular orbital calculations (Gaussian 98) showed that the electronic transition of 1 and 2 is a pi-pi* transition centered on the functionalized 8-hydroxyquinolato group and the electronic transition of 3 and 4 is an interligand charge transfer from the 2-benzothienyl ligand to the hydroxyquinolato ring. A double-layer electroluminescent device using 3 as the emitter has been fabricated, which produced a broad emission band with a significant contribution of exciplex emission.

Square planar vs tetrahedral geometry in four coordinate iron(II) complexes.

Abstract: The geometric preferences of a family of four coordinate, iron(II) d6 complexes of the general form L2FeX2 have been systematically evaluated. Treatment of Fe2(Mes)4 (Mes = 2,4,6-Me3C6H2) with monodentate phosphine and phosphite ligands furnished square planar trans-P2Fe(Mes)2 derivatives. Identification of the geometry has been accomplished by a combination of solution and solid-state magnetometry and, in two cases (P = PMe3, PEt2Ph), X-ray diffraction. In contrast, both tetrahedral and square planar coordination has been observed upon complexation of chelating phosphine ligands. A combination of crystallographic and magnetic susceptibility data for (depe)Fe(Mes)2 (depe = 1,2-bis(diethylphosphino)ethane) established a tetrahedral molecular geometry whereas SQUID magnetometry and Mossbauer spectroscopy on samples of (dppe)Fe(Mes)2 (dppe = 1,2-bis(diphenylphosphino)ethane) indicated a planar molecule. When dissolved in chlorinated solvents, the latter compound promotes chlorine atom abstraction, forming te...

Metamorphoses of Hamiltonian Systems with Symmetries

Abstract: Introduction.- Four Hamiltonian Systems.- Small Vibrations of Tetrahedral Molecules.- The Hydrogen Atom in Crossed Fields.- Quadratic Spherical Pendula.- Fractional Monodromy in the 1: - 2 Resonance System.- The Tetrahedral Group.- Local Properties of Equilibria.- References.- Index.

Synthesis and antibacterial activity of cefotaxime metal complexes

Abstract: Cefotaxime (Hcefotax) interacts with transition metal ions to give [M(cefotax)Cl] complexes (M = Mn(II), Fe(III), Co(II), Ni(II), Cu(II) and Cd(II)) which were characterized by physicochemical and spectroscopic methods and a tetrahedral geometry is suggested for their structure. The IR and the 1H-NMR spectra of the complexes suggest that the cefotaxime behaves as monoanionic tridentate ligand . The complexes have been screened for antibacterial activity against several bacteria, and the results are compared with the activity of cefotaxime

Structural and spectroscopic characterization of first-row transition metal(II) substituted blue copper model complexes with hydrotris(pyrazolyl)borate.

Abstract: [CuL(SC6F5)] (1) (L = hydrotris(3,5-diisopropyl-1-pyrazolyl)borate anion) has been reported as a good model for blue copper proteins [Kitajima, N.; Fujisawa, K.; Tanaka, M.; Moro-oka, Y. J. Am. Chem. Soc. 1992, 114, 9232−9233]. To obtain more structural and spectroscopic insight, the first-row transition metal(II) substituted complexes of Cu(II) (1) to Mn(II) (2), Fe(II) (3), Co(II) (4), Ni(II) (5), and Zn(II) (6) were synthesized and their crystal structures were determined. These model complexes have a distorted tetrahedral geometry arising from the tripodal ligand L. The d value, which is defined by the distance from the N2S basal plane to the metal(II) ion, and the bond angles such as N−M−N and S−M−N are good indicators of these structural distortions. The obtained complexes were characterized by UV−vis absorption, EPR, NMR, far-IR, and FT-Raman spectroscopies and electrochemical and magnetic properties. In UV−vis absorption spectra, the sulfur-to-metal(II) CT bands and the d−d transition bands are ob...

The crystal structure of γ-P4, a low temperature modification of white phosphorus

Abstract: The crystal structure of γ-P 4 , one of three modifications hitherto reported on white phosphorus, was determined from X-ray powder diffraction data collected at T = 123 K on a Guinier-Simon camera equipped with a cold gas blower and an image plate detector. Crystallographic data at T = 123K are: space group C2/m, a = 9.1709(5) A, b = 8.3385(5) A, c = 5.4336(2) A, and β = 90.311(3)°, V = 415.51(6) A 3 , Z = 4. The crystal structure of γ-P 4 was solved by the method of simulated annealing. The subsequent Rietveld refinement in the range 12° < 20 < 92° employing rigid-body constraints on the P 4 molecule converged at R p = 3.8, wRp = 5.0, and R F 2 =14.0%. The asymmetric unit of γ-P 4 contains three P atoms; two P atoms in a molecule are related by a mirror plane which bisects the molecule. The centers of gravity of these P 4 molecules show a distorted body-centered cubic arrangement. The four apices of the P 4 tetrahedron point to the largest possible voids formed by neighbor molecules. The difference to the crystal structures of SiF 4 and GeF 4 with an exact bcc arrangement of tetrahedral molecules is discussed as well as, in terms of layer stackings, the similarity of the structures of γ- and β-P 4 .

Group 12 metal(II) complexes with 1-methylimidazoline-2(3H)-thione (mitH): correlation between crystal structure and physicochemical property

Abstract: The crystal structures of [ZnX2(mitH)2] (X = Cl (1), Br (2)), [ZnI(mitH)3]I (3), and [CdX2 (mitH)2] (X = Cl (4), Br (5), I (6)) (mitH = 1-methylimizadoline-2(3H)-thione) were determined by X-ray crystallography and all complexes were characterized by IR, far-IR, Raman, and UV–Vis absorption (solid) spectroscopies All complexes except 3, which have a different ZnIS3 coordination mode, have a distorted tetrahedral geometry with an MX2S2 coordination mode Each π-character of the C=S bonds (from 377 to 454%) is smaller than that of free mitH (519%) Their M–S–C bond angles (from 97° to 109°) support that the C=S bonds are not a full double bond Their stretching vibration frequencies of M–S (300–320 cm−1) and M–X (229–290 cm−1) in both far-IR and Raman spectra show the lower energy shifts with increasing weight of metal(II) or halide ions Similarly, some shifts (from 275 nm for 1 to 293 nm for 6) are also observed in CT transition bands in UV-Vis absorption spectra

Synthesis, spectroscopic and the biological activity studies of thiosemicarbazones containing ferrocene and their copper(II) complexes

Abstract: Two Schiff bases, 1-acetylferrocene thiosemicarbazone (HL1) and 1,1′-diacetyl-ferrocene dithiosemicarbazone (H2L2) and their copper(II) complexes were prepared and characterized by elemental analysis, magnetic susceptibility, conductivity, and spectral (IR, UV–Vis, ESR) measurements The IR spectra showed that HL1 acts as neutral or monobasic bidentate ligand, coordinating to copper(II) through either thiono- or thiolo-sulphur and azomethine-N atoms, whereas H2L2 is a neutral or dibasic mononucleating or binucleating quadridentate ligand coordinating through the same atoms. Other spectral measurements indicate that complexes [(L1)2Cu], [(L2)Cu] and [(HL1)2Cu]X2, X = Cl, Br or ClO4 have square-planar geometry around copper(II) while [(HL1)CuX2] and [(H2L2)Cu2X4], X = Cl or Br, have distorted tetrahedral geometry. The biological activity studies of the complexes and the free ligands towards two gram positive and two gram negative bacteria and one fungal species have been studied and the potential is related ...

Electrochemical Synthesis and Structural Characterization of Silver(I) Complexes of N-2-Pyridyl Sulfonamide Ligands with Different Nuclearity: Influence of the Steric Hindrance at the Pyridine Ring and the Sulfonamide Group on the Structure of the Complexes§

Abstract: A new series of silver complexes, [AgL], of the anionic forms of potentially bidentate N-2-pyridyl sulfonamide ligands [N-(3-methyl-2-pyridyl)-p- toluenenesulfonamide (HTs3mepy), N-(3-methyl-2-pyridyl)mesitylenesulfonamide (HMs3mepy), N-(4-methyl-2-pyridyl)-p-toluenesulfonamide (HTs4mepy), and N-(6-methyl-2-pyridyl)mesitylenesulfonamide (HMs6mepy)] have been prepared by an electrochemical procedure. In addition, heteroleptic complexes of composition [AgLL′] (L′ = 1,10-phenanthroline and 2,2′-bipyridine) were obtained when the coligand L′ was added to the electrolytic phase. The complexes were characterized by microanalysis, IR and 1H NMR spectroscopy, and LSI mass spectrometry. In the cases of the compounds [Ag(Ts3mepy)]n (1), [Ag4(Ms3mepy)4] (2a), [Ag(Ms3mepy)]n (2b), [Ag4(Ms6mepy)4] (3a), [Ag2(Ms6mepy)2]n (3b), [Ag2(Ms3mepy) 2(phen)2] (5), [Ag2(Ms6mepy)2phen] (7), and [Ag2(Ts4mepy)2(bipy)2] (8), characterization was also carried out by single-crystal X-ray diffraction. Compounds 1 and 2b present a polymer structure formed by an {AgN2} digonal core. Compounds 2a and 3a are tetranuclear and also have a distorted {AgN2} digonal core. Compound 3b is based on binuclear distorted {AgN2} digonal units joined by an intermolecular sulfonyl oxygen atom to produce a stairlike polymer structure. The heteroleptic complexes 5 and 8 are dimeric with a distorted {AgN4} tetrahedral geometry, while compound 7 shows two different geometries around the metal, distorted {AgN 2} digonal and {AgN4} tetrahedral. The supramolecular structures of all species are organized by π,π-stacking, C-H⋯π, or C-H⋯O interactions.

Organotin(IV) derivatives as biocides: An investigation of structure by IR, solution NMR, electron impact MS and assessment of structure correlation with biocidal activity

Abstract: A brief account is given of the synthesis, structural chemistry and the antibacterial, antifungal and cytotoxic effects of organotin complexes of 2-[(2,4-dichloroanilinocarbonyl)]benzoic acid. The unimolar and bimolar substitution products have been characterized by elemental analysis and spectral studies, including IR, 1H NMR, 13C NMR, 119Sn NMR, and mass spectra. The data support the binding of the oxygen atom to the tin atom in [R2Sn(OOCR’)2] and [R3Sn(OOCR’)] (R = Me, Bu, and Ph, R’ = 2-[(2,4-dichloroanilinocarbonyl)]benzoic acid). Based on these studies, with a coordination number of four, a distorted tetrahedral geometry has been proposed for the resulting derivatives in solution. The free ligand (R’/COOH) and its respective tin complexes were tested in vitro against a number of microorganisms to assess their biocidal properties and to correlate them with the structures of the derivatives.

Self‐Assembly of Organotin(IV) Moieties with the Schiff‐Base Ligands Pyruvic Acid Isonicotinyl Hydrazone and Pyruvic Acid Salicylhydrazone: Synthesis, Characterization, and Crystal Structures of Monomeric or Polymeric Complexes

Abstract: A series of organotin(IV) complexes of the type [R2SnLY]2 or [R2SnL(R3SnOH)]2 [L = 4-NC5H4CON2C(CH3)CO2 or 2-HOC6H4CON2C(CH3)CO2, and Y = H2O or CH3OH] have been synthesized by the condensation reaction of R2SnO (R = Ph 1, nC8H172) or R3SnCl (R = o-ClBz 3, o-FBz 4, p-FBz 5, p-CNBz 6) with the Schiff-base ligand pyruvic acid isonicotinyl hydrazone in a 1:1 molar ratio or (R3Sn)2O (R = nBu 7, Bz 8, p-CNBz 9) or R3SnCl (R = o-ClBz 10, p-ClBz 11, p-CNBz 12) with the Schiff-base ligand pyruvic acid salicylhydrazone in a 1:1 molar ratio. All complexes were characterized by elemental analysis and IR, 1H, and 119Sn NMR spectroscopy. The crystal structures of complexes 1, 2, 3, 7, and 10 have been determined by X-ray single crystal diffraction analyses, which show that the tin atoms of 1, 2, 3, and 10 are all seven-coordinate in distorted pentagonal bipyramid geometries, of which only complex 1 exhibits an asymmetric structure containing two different types of tin atoms. The crystal structure of 7 exhibits a dimeric structure containing distannoxane units with two types of tin atoms, in which one tin atom appears to be seven-coordinate with a distorted pentagonal bipyramid geometry and the other is four-coordinate with a distorted tetrahedral geometry. A comparison of the IR spectra of the ligands with those of the corresponding complexes reveals that the ligands coordinate to tin in the enol form due to the disappearance of the bands assigned to the carbonyl group. (© Wiley-VCH Verlag GmbH and Co. KGaA, 69451 Weinheim, Germany, 2005)

Stiffness and Raman Intensity: a Conceptual and Computational DFT Study

Abstract: A DFT-based reactivity descriptor, the nuclear stiffness, is related to the Raman scattering intensity, which is experimentally accessible. The application of this new relationship obtained within certain approximations has been checked in two different sets of molecules. First, we study a favorable case, where the contribution of the anisotropy to the Raman intensity is zero (symmetric stretching mode in 15 tetrahedral molecules). Second, we consider a “worst” case scenario, where the anisotropy contribution can be expected to be important (stretching mode in 32 diatomic molecules). The numerical results clearly show a relationship between stiffness and Raman intensity reflecting the expected anisotropy influence.

Multidimensional Cyanide‐Bridged Heterometallic FeII–CuI and Homometallic CuI Coordination Polymers from Solvothermal Reactions Involving either K3[Fe(CN)6] or KCN as the Source of Cyanide Anions

Abstract: The reaction between K 3 [Fe(CN) 6 ], CuCl 2 .2H 2 O and 1,10-phenanthroline (phen) under hydrothermal conditions gives rise to the formation of the 3D cyanide-bridged heterometallic Fe I I -Cu 1 complex [Fe(CN) 4 (phen) 2 Cu 2 ](1). Its 3D network structure is constructed from two types of fused cyanide-bridged 10- and 14-metal-membered centrosymmetric rings (Fe 2 Cu 8 and Fe 2 Cu 1 2 ), which are defined by the general sequences {(Cu I ) 4 -Fe I I -(Cu I ) 4 -Fe I I ] and {(Cu I ) 6 -Fe I I -(Cu I ) 6 -Fe I I }, respectively. The copper(I) and iron(n) atoms exhibit distorted triangular planar and distorted octahedral coordination environments, respectively. Complex I is the first example of a 3D cyanide-bridged bimetallic complex prepared by hydrothermal methods. The use of methanol as solvent, KCN as source of cyanide anions and 2,2',6,6'-bipyrimidine as the bridging ligand results in the isolation of the 2D homometallic copper(i) complex [Cu 2 (CN) 2 (bpym)].H 2 O (2). Its structure consists of neutral 2D (6,3) honeycomb layers in the ab plane made of fused Cu 6 (CN) 4 (bpym) 2 rings, in which the copper(i) atoms exhibit a distorted tetrahedral geometry. The layers are interdigitated in such a way that the bpym ligands lie above and below the ring cavities of neighbouring networks, with an ABCD repeat sequence of layers. Water molecules are located in the free space between the A/D and B/ C layers. Under the same conditions as used for 1, but with 4-methyl-2,2',6,6'-bipyrimidine 2-oxide instead of phen, the 3D complex [Cu 2 (CN) 2 (mbpym] (3) was obtained (mbpym = 4-methyl-2,2',6,6'-bipyrimidine). During the reaction the oxygen atom of the N-oxide group is eliminated and the novel ligand mpym formed. Its structure consists of distorted tetrahedral copper(i) atoms connected by cyanide and mpym bridging ligands to give rise to a 3D chiral network.

Infrared spectrum and structure of the Hf(OH)4 molecule.

Abstract: Laser-ablated Hf atoms react with H2O2 and with H2 + O2 mixtures in solid argon to form the Hf(OH)2 and Hf(OH)4 molecules, which are identified from the effect of isotopic substitution on the matrix infrared spectra. Electronic structure calculations at the MP2 level varying all bond lengths and angles converge to nearly linear and tetrahedral molecules, respectively, and predict frequencies for these new product molecules and mixed isotopic substituted molecules of lower symmetry that are in excellent agreement with observed values, which confirms the identification of these hafnium hydroxide molecules. This work provides the first evidence for a metal tetrahydroxide molecule and shows that the metal atom reaction with H2O2 in excess argon can be used to form pure metal tetrahydroxide molecules, which are not stable in the solid state.

(2,2′‐Biquinoline‐κ2N,N′)dichloropalladium(II), ‐copper(II) and ‐zinc(II)

Abstract: In the three title complexes, namely (2,2'-biquinoline-κ 2 N,N')dichloropalladium(II), [PdCl 2 (C 18 H 12 N 2 )], (I), and the corresponding copper(II), [CuCl 2 (C 18 H 12 N 2 )], (II), and zinc(II) complexes, [ZnCl 2 (C 18 H 12 N 2 )], (III), each metal atom is four-coordinate and bonded by two N atoms of a 2,2'-biquinoline molecule and two Cl atoms. The Pd II atom has a distorted cis-square-planar coordination geometry, whereas the Cu II and Zn II atoms both have a distorted tetrahedral geometry. The dihedral angles between the N-M-N and Cl-M-Cl planes are 14.53 (13), 65.42 (15) and 85.19 (9)° for (I), (II) and (III), respectively. The structure of (II) has twofold imposed symmetry.

Triplet Acetylenes as Synthetic Equivalents of 1,2‐Bicarbenes, Part II: New Supramolecular Scaffolds from Photochemical Cycloaddition of Diarylacetylenes to 1,4‐Cyclohexadienes

Abstract: 1,5-Diaryl substituted homoquadricyclanes which are readily available through cascade photocycloaddition of diarylacetylenes to 1,4-cyclohexadienes are useful supramolecular scaffolds with an angle of about 60 degrees formed by the two aromatic rings defining a hydrophobic cavity. These structural features of pyridinyl homoquadricyclanes were applied to the design of composite organic/inorganic materials with topologies depending on the ratio of ligand to metal. The crystal structure of complex 1 (L1/AgNO(3) in a 1:1 ratio) shows an alternating ligand-metal polymer in which each of the silver ions in its linear coordination geometry is shared between two L1 molecules. A small change in the crystallization method yields a supramolecular rhomboid (complex 2, L1/AgNO(3) 3:2 ratio) which has two ligands that occupy opposite corners of the rhomboid and two silver atoms occupy the other two corners. Connection of the rhomboids units through a third molecule forms unique "beads on a string" polymeric chains. In complex 2, the silver ions adopt a distorted tetrahedral geometry with the nitrate anion occupying one of the vertices of the tetrahedron. The crystal packing of the chain of rhomboids generates cavities which are filled with disordered solvent molecules. Non-symmetrical homoquadricyclane L3 coordinates with silver only through the nitrogen of the pyridine ring but not through the nitrogen of the tetrafluoropyridine ring in which the electron density of the nitrogen lone-pair is very low. The substituents on the polycyclic moiety of the homoquadricyclane cause restricted rotation of the pyridine rings which suggests that the flexibility of such systems can be fine-tuned to create a family of supramolecular scaffolds of controlled rigidity.

Ab initio density-functional study of the bridging addition of acrylonitrile on the Si(100) surface.

Abstract: Acrylonitrile may react with the Si(100) surface in a number of ways. Fifteen different configurations have been identified. This study which complements an earlier study devoted to cycloadditions and bonds involving a single atom deals essentially with configurations involving cumulative double bonds. Factors affecting the relative stability of various mesomeric forms are shown to be the proximity to tetrahedral geometry and the compatibility of the dipole form with buckled structures. Tripods are shown to be a way to accommodate a priori unfavorable structures.