Bridging O-atom Research Articles

Retraction of "Pushing Single-Oxygen-Atom-Bridged Bimetallic Systems to the Right: A Cryptand-Encapsulated Co-O-Co Unit".

A dicobalt(II) complex, [Co2(mBDCA-5t)](2-) (1), demonstrates a cofacial arrangement of trigonal monopyramidal Co(II) ions with an inter-metal separation of 6.2710(6) A. Reaction of 1 with potassium superoxide generates an encapsulated Co-O-Co core in the dianionic complex, [Co2O(mBDCA-5t)](2-) (2); to form the linear Co-O-Co core, the inter-metal distance has diminished to 3.994(3) A. Co K-edge X-ray absorption spectroscopy data are consistent with a +2 oxidation state assignment for Co in both 1 and 2. Multireference complete active space calculations followed by second-order perturbation theory support this assignment, with hole equivalents residing on the bridging O-atom and on the cryptand ligand for the case of 2. Complex 2 acts as a 2-e(-) oxidant toward substrates including CO and H2, in both cases efficiently regenerating 1 in what represent net oxygen-atom-transfer reactions. This dicobalt system also functions as a catalase upon treatment with H2O2.

Pushing Single-Oxygen-Atom-Bridged Bimetallic Systems to the Right: A Cryptand-Encapsulated Co-O-Co Unit.

A dicobalt(II) complex, [Co2(mBDCA-5t)](2-) (1), demonstrates a cofacial arrangement of trigonal monopyramidal Co(II) ions with an inter-metal separation of 6.2710(6) Å. Reaction of 1 with potassium superoxide generates an encapsulated Co-O-Co core in the dianionic complex, [Co2O(mBDCA-5t)](2-) (2); to form the linear Co-O-Co core, the inter-metal distance has diminished to 3.994(3) Å. Co K-edge X-ray absorption spectroscopy data are consistent with a +2 oxidation state assignment for Co in both 1 and 2. Multireference complete active space calculations followed by second-order perturbation theory support this assignment, with hole equivalents residing on the bridging O-atom and on the cryptand ligand for the case of 2. Complex 2 acts as a 2-e(-) oxidant toward substrates including CO and H2, in both cases efficiently regenerating 1 in what represent net oxygen-atom-transfer reactions. This dicobalt system also functions as a catalase upon treatment with H2O2.

Poly[bis(μ-2-amino-4-nitrobenzoato)di-μ-aqua-dirubidium

In the structure of the title salt, [Rb2(C7H5N2O4)2(H2O)2]n, the asymmetric unit comprises two independent and different seven-coordinate Rb+ cations, one forming an RbO7 polyhedron, the other a RbO6N polyhedron, each of which is considerably distorted. The RbO7 polyhedron comprises bridging O-atom donors from two water mol­ecules, three carboxyl­ate groups, and two nitro groups. The RbO6N polyhedron comprises the two bridging water mol­ecules, one monodentate amine N-atom donor, one carboxyl O-atom donor and three O-atom donors from nitro groups (one from the chelate bridge). The extension of the dinuclear unit gives a three-dimensional polymeric structure which is stabilized by both intra- and inter­molecular amine N—H⋯O and water O—H⋯O hydrogen bonds to carboxyl and water O-atom acceptors, as well as a number of inter-ring π–π inter­actions [minimum centroid–centroid separation = 3.364 (2) Å]. The title salt is isostructural with the analogous caesium salt.

Coordination polymeric structures in the sodium salt of 4-chloro-3-nitrobenzoic acid and the sodium and potassium salts of 4-nitroanthranilic acid

The structures of the hydrated sodium salts of 4-chloro-3-nitrobenzoic acid {poly[aqua(μ4-4-chloro-3-nitrobenzoato)sodium(I)], [Na(C7H3ClNO4)(H2O)]n, (I)} and 2-amino-4-nitrobenzoic acid {poly[μ-aqua-aqua(μ3-2-amino-4-nitrobenzoato)sodium(I)], [Na(C7H5N2O4)(H2O)2]n, (II)}, and the hydrated potassium salt of 2-amino-4-nitrobenzoic acid {poly[μ-aqua-aqua(μ5-2-amino-4-nitrobenzoato)potassium(I)], [K(C7H5N2O4)(H2O)]n, (III)} have been determined and their complex polymeric structures described. All three structures are stabilized by intra- and intermolecular hydrogen bonding and strong π-π ring interactions. In the structure of (I), the distorted trigonal bipyrimidal NaO5 coordination polyhedron comprises a monodentate water molecule and four bridging carboxylate O-atom donors, generating a two-dimensional polymeric structure lying parallel to (001). Intra-layer hydrogen-bonding associations and strong inter-ring π-π interactions are present. Structure (II) has a distorted octahedral NaO6 stereochemistry, with four bridging O-atom donors, two from a single carboxylate group and two from a single nitro group and three from the two water molecules, one of which is bridging. Na centres are linked through centrosymmetric four-membered duplex water bridges and through 18-membered duplex head-to-tail ligand bridges. Similar centrosymmetric bridges are found in the structure of (III), and in both (II) and (III) strong inter-ring π-π interactions are found. A two-dimensional layered structure lying parallel to (010) is generated in (II), whereas in (III) the structure is three-dimensional. With (III), the irregular KO7 coordination polyhedron comprises a doubly bridging water molecule, a single bidentate bridging carboxylate O-atom donor and three bridging O-atom donors from the two nitro groups. A three-dimensional structure is generated. These coordination polymer structures are among the few examples of metal complexes of any type with either 4-chloro-3-nitrobenzoic acid or 4-nitroanthranilic acid.

DFT Study of the Adsorption of Aspartic Acid on Pure, N-Doped, and Ca-Doped Rutile (110) Surfaces

Understanding the interaction mechanism between titanium oxide surfaces and proteins/peptides/amino acids is crucial to the success of Ti implants. Aspartic acid (abbreviated as Asp or D) is one of the most abundant amino acid in nature. In this study, Dmol3, a quantum mechanics first-principles density functional theory code, was employed to investigate the interaction of Asp with pure, nitrogen-doped, and calcium-doped rutile (R(110)) surfaces. The effect of water on the interaction was also studied. The adsorption energy analysis demonstrated that the strongest adsorption happened when both the amino and carboxyl groups of Asp approached the R(110) surfaces and formed a bidentate coordination to two surface Ti atoms. Hydrogen bonds from the H atoms of Asp and bridging-O atoms on the surface also contributed to the adsorption. Water hindered the Asp adsorption. N-doping and Ca-doping were not beneficial to Asp adsorption. The results imply that we may realize selective protein/peptide/amino acid adsorption on materials and determine the adsorption of specific biomolecules by an elaborately designed ion doping process. Our results could have potential impact on the design of effective material surface treatments for biomedical applications.

The structure of crystals, glasses, and melts along the CaO-Al2O3 join: Results from Raman, Al L- and K-edge X-ray absorption, and 27Al NMR spectroscopy

Calcium aluminate glasses are important materials where AlO 4/2 − is the only network former. Aluminum in crystals or glasses between CaO and Al 2 O 3 can have different environments as a function of the CaO/Al 2 O 3 ratio. Using X-ray absorption at the Al K - and L -edges, Raman and 27 Al NMR spectroscopies, we have determined the structural surroundings of Al in glasses, crystals, and melts in this binary system. Aluminum is in octahedral coordination at high-Al 2 O 3 content (>80 mol%) and essentially in fourfold coordination with 4 bridging O atoms (BOs) at Al 2 O 3 contents between 30 and 75 mol%. At around 25 mol% Al 2 O 3 , Al is in tetrahedral coordination with two BOs. The presence of higher-coordinated species at high-Al 2 O 3 contents and their absence at low Al 2 O 3 imply different viscous flow mechanisms for high- and low-concentration Al 2 O 3 networks.

A Combined Experimental and Theoretical Charge Density Study of the Chemical Bonding and Magnetism in 3-Amino-propanolato Cu(II) Complexes Containing Weakly Coordinated Anions

The experimental (100 K) and theoretical charge densities in the binuclear complexes [Cu2(ap)2(L)2] (ap = 3-aminopropanolate) 1 (L = nitrite), 2 (L = nitrate), and 3 (L = formate) have been examined. These complexes contain the same centrosymmetric alkoxy-bridged motif, where each strongly Jahn-Teller distorted Cu(II) ion is ligated to three O atoms and one N atom in a square-planar arrangement. This primary coordination sphere is augmented by a long contact with the O atom of a pendant L anion from an adjacent molecule in the crystal lattice. Topological analyses of the experimental and theoretical densities according to the quantum theory of atoms in molecules (QTAIM) are in excellent agreement. Consideration of a number of topological indicators including rho(r), vector differential(2)rho(r), the delocalization indices delta(A,B), and the contour integral(A intersection B) rho(r) of the density over the zero flux surface shared by the two atoms confirms that the Cu-O and Cu-N bonding in the primary coordination sphere has a strong covalent component, but the weak Cu...O interactions are primarily electrostatic in nature. In this first investigation of the source function in a coordination complex, it is shown to provide an insight into the differing electrostatic and covalent contributions to the chemical bonds. The two Cu(II) centers are strongly antiferromagnetically coupled, but the topological analyses indicates the lack of any direct Cu...Cu interaction. The molecular graph suggests an exchange pathway via the bridging O-atoms, thus providing experimental support of the classical superexchange mechanism. Periodic DFT calculations on 2 and 3 show that the intradimer coupling proceeds via spin-delocalization and provide values of the magnetic coupling constants -2 J of 324.5 and 244.8 cm(-1), respectively, which compare well with the previously determined experimental values.

Structure of Zirconium-Exchanged H-ZSM5 Prepared by Vapor Exchange of ZrCl4

Zr dimers (Zr2O32+) interacting with two exchange sites and uniform in structure were prepared by grafting anhydrous ZrCl4(g) onto H-ZSM5 followed by hydrolysis and dehydration. This method led to selective exchange, without concurrent formation of crystalline ZrO2 aggregates, ubiquitously formed via aqueous exchange because of the slow diffusion of aquo oxo-ions within small channels. ZrCl4(g) reacts with acidic OH groups to form HCl and ZrCl3+-ZSM5 species. This exchange stoichiometry was confirmed by the number of HCl molecules evolved during hydrolysis, a process that forms ZrO(OH)+ species. These species then dehydroxylate via condensation with vicinal ZrO(OH)+ to form (OZr−O−ZrO)2+ species interacting with two exchange sites and containing one bridging O-atom. This exchange process is consistent with the number of residual OH groups titrated by D2 and with the intensity of O−H infrared bands. X-ray diffraction, 27Al nuclear magnetic resonance, and infrared spectra showed that the exchange process did not influence zeolite crystallinity, led to Zr4+ introduction into the zeolite framework, or form residual Zr(OH)x species at exchange sites. Weak Raman bands in the 960−1030 cm-1 region, absent in crystalline ZrO2 and H-ZSM5, were detected upon exchange. The maximum attainable Zrdimer/Alf exchange ratios (0.6 ± 0.05) are consistent with Al radial structure distributions and with expected Al−Al distances required to anchor (OZr−O−ZrO)2+ species in ZSM-5 with a statistical distribution of Al atoms. ZrCl4 species in excess of this saturation stoichiometry formed monoclinic ZrO2, detectable in Raman spectra and X-ray diffraction patterns.

Electronic structure of SiO2: Charge redistribution contributions to the dynamic dipoles/effective charges of the infrared active normal modes

This article applies ab initio calculations at the (i) Hartree–Fock self-consistent field single determinant and (ii) configuration interaction multideterminant expansion levels to study the diagonal components of the dynamic dipoles, Δμi/Δqj with i=j, or equivalently infrared effective charges, ei*, associated with asymmetric bond stretching νy, symmetric bond stretching νz, and out-of-plane bond rocking νx, normal mode infrared active vibrations of noncrystalline SiO2. The normal mode dynamic dipoles (hereafter, Δμ/qi) are decomposed into equilibrium charge density (ionic) and orbital variation (charge redistribution) contributions. The calculations are based on small clusters in which Si–O–Si groups are connected through O atoms to embedding Si atom terminators Si* that emulate the connectivity of these Si–O–Si groups to the SiO2 continuous random network. Values of Δμ/Δqi have been determined as a function of the Si–O–Si bond angle α at the bridging O-atom sites, and agree with values obtained from analysis of infrared spectra. Finally, the ab initio calculations are extended to noncrystalline silicon–carbon alloys and silicon nitride, and values of Δμ/Δqi are determined for infrared active vibrations associated with N- and C-atom asymmetric stretching normal mode motions. The normalized equilibrium charge density or ionic contributions of the O, N, and C atoms follow trends expected on the basis of their relative Pauling electronegativities in bonds with Si.

Synthesis and Structure of Ln(W5O18)-Capped Mixed-Ligand Polyoxotungstolanthanoate [Ln(W5O18){Ln(H2O)2(SbW9O33)(W5O18)}]15−(Ln = Sm and Er)

Abstract Polyoxotungstolanthanoate, [Ln2(H2O)2(SbW9O33)(W5O18)2]15− (Ln = Sm and Er), possessing Ln3+, trivacant α-B-Keggin [SbW9O33]9−, and monovacant Lindqvist [W5O18]6− groups with a ratio of 2 : 1 : 2, was prepared and structurally characterized. In the anion the α-B-[SbW9O33]9− group coordinates to two [Ln(W5O18)]3− moieties through terminal- and bridging-O atoms at vacant and non-vacant sites, respectively. A 183W-NMR spectrum for Y3+-analog in aqueous solution was consistent with this anion structure.

A Reinvestigation of the Structure and Torsional Potential of N2O5 by Gas-Phase Electron Diffraction Augmented byAb Initio Theoretical Calculations

Gaseous N2O5 consists of two NO2 groups bonded to a bridging O-atom to form a nonlinear N−O−N moiety. The NO2 groups undergo slightly hindered internal rotation around the bonds to the bridge so that instantaneous composition of the gaseous system is characterized by molecules with all combinations of torsion angles. In an earlier investigation, an attempt was made to determine the coefficients for an empirical form of the double-rotor torsional potential, and the bond lengths and bond angles measured subject to assumptions that the structure of the O−NO2 groups was invariant to torsion angle and that these groups had C2v symmetry. The system has now been reinvestigated in terms of a more realistic model in which this symmetry restriction was relaxed, account was taken of structural changes in the NO2 groups with torsion angle as predicted by ab initio theory at the B3LYP/6-311+G* level, and a more convenient form of the torsional potential was assumed. The most stable conformation has C2 symmetry with torsion angles τ1 (defined as ∢(N−O−N=O4)) equal to τ2 (defined as ∢(N−O−N=O6)) equal to 33.7°; because of the broad potential minimum in this region, the uncertainty in these angles is difficult to estimate, but is probably 3 – 4°. The results for the bond lengths and bond angles for the most stable conformation are rg(N−O)=1.505(4) A, rg(N=O)=1.188(2) A, ∢α(N−O−N)=112.3(17)°, ∢α(O=N=O)=134.2(4)°, 〈∢α(O−N=O)〉=112.8(2)°. The difference between the symmetry-nonequivalent O−N=O angles is estimated to be ca. 6.7° with the larger angle positioning the two N=O bonds on different NO2 groups nearest each other. These average values are similar to those obtained in the original study. The main difference is found in the shape of the torsional potential, which at τ1/τ2=0/0 has a saddle point in the present work and a substantial peak in the earlier. The implication of the torsion-angle findings for electron-diffraction investigations of this type is discussed.

ChemInform Abstract: BONDING CAPABILITIES OF THE BIOCHEMICAL BUFFER TRIS TOWARD COPPER(II) ION. STRUCTURE AND MAGNETIC PROPERTIES OF BINUCLEAR AND TETRANUCLEAR SYSTEMS

AbstractRöntgenstrukturanalysen für die bei der Reaktion zwischen C u(ll)‐halogeniden und dem als Komplexbildner fungierenden Puffer Tris‐[hydroxymethyllmethylamin in Abhängigkeit vom stöchiometrischen Verhältnis gebildeten Komplexe (I) und (II) werden durchgeführt.

Chloroantimonate(III), V. Darstellung und Kristallstruktur des Triethanolammoniuin-tetrachloroantimonats [(C2H4OH)3NH]SbCl4 / Chloroantimonates(III), V. Preparation and Crystal Structure of Triethanolammonium Tetrachloroantimonate [(C2H4OH)3NH]SbCl4

Triethanolammonium tetrachloroantimonate was synthesized and investigated by X-ray diffrac­tion analysis. The structure consists of SbCl3 molecules, chloride ions and triethanolammonium cations. The SbCl3 molecules and the cations form adducts by a bridging O-atom at 274.3 pm. The Sb-Cl distances within the SbCl3 molecule are 239.2, 240.3 and 245.3 pm, whereas the distances from the Sb atom th the Cl- ion are 290.2 and 332.1 pm.