A theoretical study of photoinduced electron transfer between tetracyanoethylene and arene

 Ab initio calculations have been performed to investigate the state transition in photoinduced electron transfer reactions between tetracyanoethylene and biphenyl as well as naphthalene. Face-to-face conformations of electron donor–acceptor (EDA) complexes were selected for this purpose. The geometries of the EDA complexes were determined by using the isolated optimized geometries of the donor and the acceptor to search for the maximum stabilization energy along the center-to-center distance. The correction of interaction energies for basis set superposition error was considered by using counterpoise methods. The ground and excited states of the EDA complexes were optimized with complete-active-space self-consistent-field calculations. The theoretical study of the ground state and excited states of the EDA complex in this work reveals that the S₁ and S₂ states of the EDA complexes are charge–transfer (CT) excited states, and CT absorption which corresponds to the S₀→S₁ and S₀→S₂ transitions arise from π−π^* excitation. On the basis of an Onsager model, CT absorption in dichloromethane was investigated by considering the solvent reorganization energy. Detailed discussions on the excited state and on the CT absorptions were made. Received: 30 April 2001 / Accepted: 18 October 2001 / Published online: 9 January 2002     

Synthesis and characterization of mono- and dinuclear copper(I) complexes with 3-(2-pyrimidinyl)-1,2,4-triazine

The mono- and dinuclear Cu(I) complexes [CuI(PPh₃)(pmtz)] (1) and [{Cu(PPh₃)₂}₂(μ-pmtz)](ClO₄)₂ (2), where pmtz is 3-(2-pyrimidinyl)-1,2,4-triazine, have been synthesized and characterized. Single-crystal X-ray diffraction analysis reveals that the pmtz acts as a bidentate ligand in complex 1, whereas in complex 2 the pmtz coordinates as a bis-bidentate chelate, assembling two identical {Cu(PPh₃)₂} moieties into a copper(I) dimer with a triple-decker sandwich structure involving phenyl/pmtz/phenyl π–π interactions. The UV–vis spectra of complexes 1 and 2 show low-energy absorptions at 350–550 nm, assigned to the Cu(I) to pmtz MLCT transition, probably mixed with some XLCT character for 1. The absorption of 2 is blue-shifted relative to that of 1 due to the substitution of the iodide of 1 with the π-acceptor ligand PPh₃. Complexes 1 and 2 are non-emissive, both in solution and in the solid state, most likely owing to the electronic effects induced by the additional nitrogen donor of pmtz compared to 2,2′-bipyrimidine.     

Interaction of nicotine with π and σ electron acceptors

Interaction of nicotine with tetracyanoethylene and iodine was investigated spectrophotometrically and found to form strong CT complexes (n−π and n-σ^*, respectively). The donor site involved in CT interaction is the pyrrolidine nitrogen. The nicotine-I₂ complex exists as the ionic structure (nicotine) I⁺-I ₃ ⁻ . Formation constants of the CT complexes in various solvents were determined from 10 to 25°C and are discussed in terms of the nature of the electron acceptor and solvent polarity. Solid CT complexes were synthesized and were characterized by microchemical analysis and infrared spectra techniques.     

Two manganese(II) complexes based on anthracene-9-carboxylate: Syntheses,crystal structures,and magnetic properties

Abstract  To explore the influence of the anthracene ring skeleton, with a large conjugated π-system, on the structures and properties of its complexes, two Mn^II complexes with anthracene-9-carboxylate ligand were synthesized and structurally characterized: {[Mn(L)₂(H₂O)₂](H₂O)}_∞ (1) and [Mn₂(L)₄(phen)₂(μ-H₂O)](CH₃OH) (2) (L = anthracene-9-carboxylate and phen = 1,10-phenanthroline). Complex (1) has a one-dimensional (1D) chain structure that is further assembled to form a two-dimensional (2D) sheet, and then an overall three-dimensional (3D) network by π···π stacking and/or C–H···π interactions. Complex (2) makes a dinuclear structure by incorporating the chelating phen ligand, which is further interlinked via inter-molecular π···π stacking and C–H···π interactions to generate a higher-dimensional supramolecular network along the different crystallographic directions. The results reveal that the bulky anthracene ring skeleton in L, by virtue of intra- and/or inter-molecular π···π stacking and C–H···π interactions, plays an important role in the formation of complexes (1) and (2). The magnetic properties of (1) and (2) were further investigated. As expected, the very long inter-metallic separations result in weak magnetic coupling, with the corresponding coupling constant values of J = −10 cm⁻¹ for (1) and J = −2.46 cm⁻¹ for (2). Graphical abstract  The constructions of two new Mn^II complexes comprising 1D chain (1) and dinuclear subunit (2) structures have been successfully achieved by using a bulky anthracene-9-carboxylic acid (HL), together with incorporating the chelating 1,10-phenanthroline as a co-ligand for (2). The result reveals that the bulky anthracene ring skeleton of HL, by virtue of intra- and/or inter-molecular π···π stacking and C–H···π interactions, plays an important role in the formation of the supramolecular architectures of (1) and (2). Moreover, magnetic properties of the complexes have been investigated.      

Preparation of metal Niacin complexes and characterization using spectroscopic and electrochemical techniques

Metal complexes of Niacin (3-pyridin carboxylic acid) were prepared in aqueous medium and characterized by different physico-chemical methods. On the basis of elemental analysis the empirical formula of the complexes have been proposed as [Fe(C₆H₄NO₂)]Cl₂, [Co(C₆H₄NO₂)]Cl, [Zn(C₆H₄NO₂)]Cl, [Cd(C₆H₄NO₂)]Cl and [Hg(C₆H₄NO₂)]Cl. IR spectral data indicate that the metal-ligand bonding occurs through nitrogen atom of aromatic ring and oxygen atom of COO⁻-group. UV-visible spectra show that Fe(III) and Co(II) complexes show d-d electronic transition in addition to π → π*, n → π* and n → σ* transitions. The Fe(II) and Co(II) complexes are paramagnetic. QSTG analysis data strongly support the absence of water molecules in the complexes, and the weight of the residue corresponds to the respective metal oxides. Cyclic voltammetric studies suggest that the redox properties of Zn(II), Cd(II) and Hg(II) in their complexes are modified compared to the uncoordinated metal ion. The CV data also indicate that the charge transfer processes are not reversible.     

Synthesis,structures, photoluminescence,and theoretical investigations on two new Zn(II)/Mn(II) complexes with pyridine-2-amidoxine and carboxylate ligands

Abstract  

Two new neutral mononuclear Zn(II) and Mn(II) complexes with pyridine-2-amidoxine and carboxylate ligands, [Zn(paH)₂(OAc)₂]·2CH₃OH (paH = pyridine-2-amidoxine, HOAc = acetic acid) (1), and [Mn(paH)₂(OAc)₂]·C₂H₅OH·2H₂O (2), have been prepared and characterized structurally by X-ray crystallography. 1 and free paH exhibit photoluminescence at room temperature in solid state, which is rare so fare for metal complexes with oxime-based ligand. The emissions of 1 and free paH arise from the metal-perturbed paH-based π → π* ligand-to-ligand charge transfer transition (LLCT) and π → π* charge transfer transition in nature, respectively, in terms of the density functional theory level calculations and molecular orbital analyses.     

Ab initio study of long-range electron transfer between biphenyl anion radical and naphthalene

After the separation of the donor, the acceptor, and the σ-type bridge from the π-σ-π system, the geometries of biphenyl, biphenyl anion radical, naphthalene, and naphthalene anion radical are optimized, and then the reorganization energy for the intermolecular electron transfer (ET) at the levels of HF/4-31G and HF/DZP is calculated. The ET matrix elements of the self-exchange reactions of theπ-σ-π systems have been calculated by means of both the direct calculation based on the variational principle, and the transition energy between the molecular orbitals at the linear coordinateR = 0.5. For the cross reactions, the ET matrix element and the geometry of the transition state are determined by searching the minimum energy splitting Δ_min along the reaction coordinate. In the evaluation of the solvent reorganization energy of the ET in solution, the Marcus’ two- sphere model has been invoked. A few of ET rate constants for the intramolecular ET reactions for the π-σ-π systems, which contain the biphenylyl as the donor and both biphenylyl and naphthyl as the acceptor, have been obtained. Project supported by the National Natural Science Foundation of China (Grant Nos. 29706104 and 29573112), the State Key Laboratory of Theoretical and Computational Chemistry of Jilin University.     

Syntheses and structures of nickel(II) and copper(II) complexes with biacetyl bis(benzoylhydrazone): one-dimensional self-assembly via π–π interaction and hydrogen bonding

Reactions of Ni(O₂CCH₃)₂·4H₂O and Cu(O₂CCH₃)₂·H₂O with biacetyl bis(benzoylhydrazone) (H₂babh) in alcoholic media afford mononuclear nickel(II) and copper(II) complexes of general formula [M(babh)]. The complexes have been characterized by microanalysis (C, H, N), magnetic susceptibility, and various spectroscopic measurements. X-ray structures of both complexes have been determined. The metal centre in [Ni(babh)] is in square-planar N₂O₂ environment provided by the tetradentate babh²⁻. On the other hand, [Cu(babh)] crystallizes as distorted square-pyramidal [Cu(babh)(CH₃OH)] from methanol. Here the tetradentate babh²⁻ constitutes the N₂O₂ square-base and the O-coordinating methanol occupies the apical site. In the crystal lattice, the molecules of [Ni(babh)] form a one-dimensional π-stacked structure. The [Cu(babh)(CH₃OH)] molecules also form a one-dimensional structure with alternating long and short Cu···Cu distances via intermolecular O–H···N hydrogen bonding and π–π interaction.     

Hydrothermal syntheses and characterization of cobalt(II) and nickel(II) complexes of 1,3-adamantanedicarboxylic acid and 1,10-phenanthroline

Two coordination complexes, namely [Co(phen)(H₂O)L]·H₂O and [Ni₂(phen)₂(H₂O)₂L₂]·4H₂O (phen = 1,10-phenanthroline, H₂L = 1,3-adamantanedicarboxylic acid) have been hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction. [Co(phen)(H₂O)L]·H₂O consists of 1D chains of the complex plus lattice H₂O molecules. Interchain hydrogen bonds and π–π stacking interactions assemble the 1D chains into 2D layers. [Ni₂(phen)₂(H₂O)₂L₂]·4H₂O is a binuclear complex which is assembled into a 3D supramolecular structure by strong hydrogen bonds and π–π stacking interactions. Both complexes were characterized by physico-chemical and spectroscopic methods.     

Intramolecular MLOH/π and MLNH/π interactions in crystal structures of metal complexes

Intramolecular metal-ligand OH/π (MLOH/π) and metal-ligand NH/π (MLNH/π) interactions in transition metal complexes between aqua or ammine ligand and ligand containing a C6-aromatic ring were investigated in crystal structures deposited in the Cambridge Structural Database (CSD). These intramolecular interactions appear in 38 structures with aqua ligand as the hydrogen atom donor and in 10 structures with ammine ligand as the hydrogen atom donor. Among all these complexes only one is negatively charged, 14 are positively charged and 33 are neutral indicating that the overall charge of the molecule has an influence on the XH/π (X = O or N) interactions. Energy estimated by DFT calculations is approximately 19 kJ mol⁻¹ for the MLOH/π interactions and approximately 15 kJ mol⁻¹ for the MLNH/π interactions. Dedicated to Professor Milan Melník on the occasion of his 70th birthday     

Chiral model complexes for methane monooxygenase and their asymmetric catalysis of styrene epoxidation

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Effect of the Counter Anion and Solvate on the Structure,Stability and Spectral Properties of a Ruthenium(II) Complex Containing Group 15 Donors and 2,2′ :6′,2′′-terpyridine

Ruthenium complexes [Ru(κ³−tpy)(AsPh₃)₂C1]PF₆ · 0.42H₂O (tpy =2,2′:6′,2′′-terpyridine) (1) and a new crystal form of [Ru(κ³−tpy)(AsPh₃)₂Cl]BF₄ (2), which crystallized without water solvate, and their comparative studies on spectral, structure and stability aspects are reported. The complexes have been characterized by elemental analyses, FAB-MS, i.r., ¹H n.m.r. and electronic spectral studies. In these complexes weak C—H···Fπ and face-to-face π–π interactions lead to a single helical motif while, C—H···FX (X=F, Cl) interactions result in linear chains. Various studies on the stability of the complexes suggested that the compound containing the counter anion PF₆^- is more stable than the other containing BF₄^- as the counterpart.     

Sandwich complexes of Si, Ge, Sn, and Pb with cyclopentadienyl type derivatives of corannulene and fullerene C60: stability estimates and molecular and electronic structure prediction by the MNDO/PM3 method

The ability of cyclopentadienyl type derivatives of corannulene C₂₀H₁₀ and fullereneI _h -C₆₀ to form η⁵-π-complexes and the problem of their existence is discussed. MNDO/PM3 calculations of half-sandwich complexes η⁵-π-MC₂₀H₁₅, η⁵-π-MC₂₀H ₁₅ ⁺ , η⁵-π-MC₆₀H₅, η⁵-π-MC₆₀H₅ and sandwich complexes 2η⁵-π-M(C₂₀H₁₅)₂, 2η⁵-π-M(C₂₀H₁₅)₂, 2η⁵-π-M(C₆₀H₅)₂ (M=Si, Ge, Sn, Pb) were performed. For all systems studied, local minima were found on corresponding potential energy surfaces and the heats of formation, geometric parameters, and distributions of effective atomic charges were calculated. Sandwich complexes are most likely to exist with M=Si and Ge. The energy and geometric characteristics of η⁵-π-complexes of corannulene were compared with those of η⁵-π-complexes of fullereneI _h -C₆₀. It was concluded that the results of quantum-chemical calculations of sandwich type corannulene derivatives can be used for simulation of the geometry and electronic structure of analogous complexes of fullereneI _h -C₆₀. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1649–1656, September, 1999.     

Syntheses,structures, and properties of two mononuclear cobalt(III) azido complexes containing a tetradentate N-donor Schiff base as end-capping ligand

Two hexacoordinated mononuclear Co(III) compounds of the type cis-[Co(L)(N₃)₂] X [1, X = ClO₄; 2, X = PF₆; L = N,N′-(bis(pyridine-2-yl)benzylidine)-1,4-butanediamine] have been synthesized and characterized by physicochemical and spectroscopic methods. The crystal structures of complexes 1 and 2 both have distorted octahedral geometry with two terminal azides in mutual cis orientations. In the crystalline state, two mononuclear units of 1 are associated by weak C–H…π interactions to produce a dimeric unit, which packs through C–H…O hydrogen bonds and π…π interactions leading to a 2-D continuum. The mononuclear units in 2 are engaged in weak cooperative intermolecular C–H…π interactions and multiple C–H…F hydrogen bonds giving rise to a 3-D network structure. These diamagnetic compounds are redox active and show luminescence in DMF solutions.     

Ethylenediamine and 1,10-phenanthroline biscyclometallated complexes of Pd(II) and Pt(II) based on 4,6-diphenylpyrimidine

Biscyclometallated [(M(N∧N))₂(μ-dphpm)](ClO₄)₂ and [(N∧N)Pd(μ-dphpm)Pt(N∧N)]Cl₂ complexes [M = Pd(II), Pt(II); (N∧N) ethylenediamine (En), 1,10-phenanthroline (phen); dphpm² — bisdeprotonated form of 4,6-diphenylpyrimidine)] have been characterized by the ¹H NMR, electronic absorption and emission spectroscopy, and also cyclic voltammetry methods. The lowest unoccupied molecular orbital (LUMO) of biscyclometallated complexes with ethylenediamine, responsible for low-energy photo- and electro-stimulated processes irrespective of the metal nature, is assigned to the π* orbital mainly localized on the pyrimidine part of the bridging ligand. In the case of complexes with phenanthroline chelating ligands, the replacement of one or two palladium metal centers [{Pd(phen)}₂(μ-dphpm)]²⁺ by platinum centers changes the LUMO nature of the complexes for the π* orbital mainly localized on the peripheral metal-complex fragment {Pt(phen)}.     

Synthesis and anion recognition of neutral receptors based on multiamide calix[4]arene

Two multiamide calix[4]arenes (5, 6) were synthesized and characterized by NMR, MS and elemental analysis. The binding properties of receptors with some anions (π-O₂NPhOPO₃²⁻, π-O₂NPhO⁻, H₂PO₄⁻, Ac⁻, Cl⁻, Br⁻ and I⁻) were studied by UV-Vis spectra. The results indicate that the tetraamide calix[4]arenes (5, 6) have a good selectivity to the anions containing aromatic ring (π-O₂NPhOPO₃ ²⁻, π-O₂NPhO⁻). The 1 : 1 complexes between host and guest were formed through multiple hydrogen bonding and π-π interactions. The hosts 5 and 6 also show a definite binding ability for the anions (H₂PO₄⁻, Ac⁻, Cl⁻) that have no ultraviolet absorption, which provides a simple method of spectrum detection for these anions.     

Synthesis and photophysical properties of luminescent mononuclear and dinuclear gold(I) complexes with ethynyl-substituted phenanthrolines

A novel asymmetric dinuclear gold(I) complex with 3,6-diethynylphenanthroline, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, has been synthesized from Au(PPh₃)Cl (PPh₃ = triphenylphosphine) and 3,6-diethynyl-1,10-phenanthroline. The asymmetrical dinuclear gold(I) complex, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, demonstrated a weak phosphorescence assignable to the metal-perturbed ³ π–π* transition in the long wavelength region compared to an intense emission of the symmetrical dinuclear complex with 3,8-diethynylphenanthroline, 3,8-bis{(PPh₃)–Au–C≡C}₂-phen. A similar tendency of phosphorescent bands for the mononuclear gold(I) complexes with 5-ethynylphenanthroline, 5-{(PPh₃)–Au–C≡C}-phen, and 3-ethynylphenanthroline, 3-{(PPh₃)–Au–C≡C}-phen was observed. The absorption bands assignable to the π–π*(C≡Cphen) transition and phosphorescent emission assignable to the metal-perturbed ³ π–π* transition for these four gold(I) complexes were reasonably consistent with the results calculated by DFT and TD-DFT.     

Synthesis, characterisation and chemical reactivity of some new dioxouranium(VI) complexes of 2-aminobenzoylhydrazone of butane-2,3-dione

A new series of dioxouranium(VI) complexes of a potential ONNO tetradentate donor 2-aminobenzoylhydrazone of butane-2,3-dione (L₁H₂) have been synthesized. At pH 2·5–4·0, the donor (L₁H₂) reacts in the keto form and complexes of the type [UO₂(L₁H₂)(X)₂] (X⁻=Cl⁻, Br⁻, NO ₃ ⁻ , NCS⁻, ClO ₄ ⁻ , CH₃COO⁻, 1/2SO ₄ ²⁻ ) are obtained. At higher pH (6·5–7), the complex of the enol form having the formula [UO₂(L₁)(H₂O)] has been isolated. On reaction with a monodentate lewis base (B), both types of complexes yield adducts of the type [UO₂(L₁)(B)]. All these complexes have been characterised adequately by elemental analyses and other standard physicochemical techniques. Location of the bonding sites of the donor molecule around the uranyl ion, status of the uranium-oxygen bond and the probable structure of the complexes have also been discussed.     

Synthesis, spectral and electrochemical study of coordination molecules Cu4OX6L4: 3-cyanopyridine Cu4OBrnCl(6?n)(3-CNpy)4 complexes

New 4-cyanopyridine halide and mixed-halide Cu₄OBr _n Cl_(6−n)(4-CNpy)₄ complexes (4-CNpy = 4-cyanopyridine, n = 0–6) were synthesised, characterised, and studied by infrared spectra, electronic spectra, and cyclic voltammetry. Infrared spectra revealed donor-acceptor vibrational couplings of the Cu₄O, Cu-Cl, and Cu-N stretching vibrations with the in-plane and out-of-plane pyridine ring vibrations. The infrared spectra, electronic spectra, and half-wave potentials correspond to a weak donor and a strong acceptor behaviour of the 4-cyanopyridine ligands and to π-back bonding, Cu(II)→pyridine rings. The results were compared with the related pyridine and 4-substituted pyridine complexes.