Acetonitrile Ligands Research Articles

Crystal structure of (aceto-nitrile-κN)iodido-(2-(naphthalen-1-yl)-6-{1-[(2,4,6-tri-methyl-phen-yl)imino]ethyl}-pyridine-κ2N,N')copper(I).

In the mononuclear title complex, [CuI(C2H3N)(C26H24N2)], the CuI ion has a distorted tetra-hedral coordination environment, defined by two N atoms of the chelating 2-(naphthalen-1-yl)-6-[(2,4,6-tri-methyl-phen-yl)imino]-pyridine ligand, one N atom of an aceto-nitrile ligand and one iodide ligand. Within the complex, there are weak intra-molecular C-H⋯N hydrogen bonds, while weak inter-molecular C-H⋯I inter-actions between complex mol-ecules, help to facilitate a three-dimensional network.

Determination of the stability constant and thermodynamic parameters between Tl+, Ag+ and Pb2+ cations with 2,6-di(furyl-2yl)-4-(4-methoxy phenyl)pyridine as a new synthesis ligand

The complexation reaction between Tl+, Ag+ and Pb2+ cations with 2,6-di(furyl-2yl)-4-(4-methoxy phenyl)pyridine as a new synthesis ligand in acetonitrile (ACN)–H2O and methanol (MeOH)–H2O binary solutions has been studied at different temperatures using conductometric method. The conductometric data show that the stoichiometry of the complexes is 1: 1 [M: L] and the stability constant of complexes changes with the binary solutions identity. Also, the structure of the resulting 1: 1 complexes was optimized using the LanL2dz basis set at the B3LYP level of theory using GAUSSIAN03 software. The results show that the change of logKf for (DFMP.Pb)2+ and (DFMP.Ag)+ complexes with the mole ratio of acetonitrile and for (DFMP.Ag)+ and (DFMP.Tl)+ complexes with the mole ratio of methanol have a linear behavior, while the change of logKf of (DFMP.Tl)+complex in ACN–H2O binary solutions (with a minimum in XACN = 0.5) and (DFMP.Ag)+ complex in MeOH–H2O binary solutions (with a minimum in XMeOH = 0.75) show a non-linear behavior. The selectivity order of DFMP ligand for these cations in mol % CAN = 25 and 75 obtain Tl+ > Pb2+ > Ag+ but in mol % CAN = 50, the selectivity order observe Pb2+ > Tl+ > Ag+. Also, this selectivity sequence of DFMP in MeOH–H2O (mol % MeOH = 75 and 100) and (mol % MeOH = 50) is obtained Pb2+ > Ag+ and Tl+ > Ag+ > Pb2+ respectively. The values of thermodynamic parameters show that these values are influenced by the nature and the composition of binary solution. In all cases, the resulting complexes are enthalpy stabilized and entropy destabilized. The TΔSC° versus ΔHC° plot of all obtained thermodynamic data shows a fairly good linear correlation which indicates the existence of enthalpy-entropy compensation in the complexation reactions.

The Influence of Metal Ion Binding on the IR Spectra of Nitrogen-Containing PAHs.

Astronomical IR emission spectra form the basis for the now widely accepted abundant presence of polycyclic aromatic hydrocarbons (PAHs) in inter- and circumstellar environments. A small but consistent frequency mismatch is found between the astronomically observed emission band near 6.2 μm and typical CC-stretching vibrations of PAHs measured in laboratory spectra near 6.3-6.4 μm. The shift of the band has been tentatively attributed to a variety of effects, among which the inclusion of heteroatoms, in particular nitrogen, in the PAH skeleton (PANH) as well as to metal ion binding to the PAH molecule. Here we experimentally investigate the combined effect of nitrogen-inclusion and metal ion binding on the IR spectra. In particular, infrared multiple-photon dissociation (IRMPD) spectra are recorded for coordination complexes of Cu+ with one or two quinoline, isoquinoline, and acridine ligands; complexes of the form Cu+(PANH) (MeCN), where the MeCN (acetonitrile) ligand acts as a relatively weakly bound "messenger" are also recorded to qualitatively verify that potential frequency shifts induced by IRMPD are minimal. The experimental IR spectra document the accuracy of IR spectral predictions by density functional theory calculations performed at the B3LYP/6-311+G(2df,2p) level and confirm that a σ-bond is formed between the copper ion and the exoskeletal N atom. The experimental spectra suggest that the CNC stretching mode undergoes a small red shift of up to 20 cm-1, with respect to the band position in the uncomplexed PANH molecule, away from the 6.2 μm interstellar position.

Ligand substitution in the osmium-antimony rings Os3(μ-SbPh2)2 (CO)10 and Os3(μ-SbPh2)3(Cl)(CO)9

TMNO-activated ligand substitution in the fused ring compounds Os3(μ-SbPh2)2(CO)10, 1, and Os3(μ-SbPh2)3(Cl)(CO)9, 2, in acetonitrile affords the mono- and disubstituted CH3CN-derivatives. The initial product of CH3CN substitution in 1 is an equatorial isomer, which can isomerize to the axial isomer upon heating; they are the first examples in which both isomers have been characterized crystallographically. Subsequent reaction of the CH3CN-derivatives of 2 with two-electron donor ligands L do not always result in the displacement of the acetonitrile ligands; displacement of a carbonyl ligand can also occur and appears to depend on the stereoelectronic properties of L. This is suggestive of an associative mechanism.

Crystal structure of cis-[PdCl2(CNMes)2

The interaction between PdCl2(CH3CN)2 and 2,4,6-Me3C6H2NC (MesNC) proceeds with the substitution of acetonitrile ligands and leads to the synthesis of a cis-[PdCl2(MesNC)2] complex. The structure of this compound is determined by single crystal X-ray diffraction (XRD). The complex has a slightly distorted square-planar structure of the metal center with two cis-positioned isocyanide ligands. In both CN isocyanide moieties the triple bonds have lengths similar to the lengths of the respective bonds in other isocyanide complexes. In the structure, the cis-[PdCl2(MesNC)2] complexes are bound by weak С–H∙∙∙Cl hydrogen bonds and π-stacking interactions.

A Density Functional Theory Study on the Ligand Substitution Mechanism of a Square Planar Pd Complex

The mechanisms of ligand substitution reactions of PdCl2 (CH3CN)2 with PPh3 and P(OPh)3 ligands were investigated by computational calculations using density functional theory (DFT). Contrary to the conventional associative mechanism of a 16‐electron Pd complex, substitutions of two acetonitrile ligands in PdCl2 (CH3CN)2 with PPh3 or P(OPh)3 adopt dissociative pathways. The first PdCl2 (CH3CN)2 + PPh3 → PdCl2 (CH3CN)(PPh3 ) + CH3CN step takes I d mechanism and the following PdCl2 (CH3CN)(PPh3 ) → PdCl2 (PPh3 )2 + CH3CN step does D mechanism. The overall free energy barriers (ΔG max ‡) of two separate steps were 26.4 and 20.4 kcal/mol, respectively. Similar reaction with P(OPh)3 ligands takes D mechanism for both first and second substitutions with ΔG max ‡ values of 30.3 and 21.0 kcal/mol, respectively.

Controlling Coordination Geometries: Ru-Carbene Complexes with Tetra-NHC Ligands.

The synthesis of the first ruthenium(II) complexes bearing open-chain tetra-N-heterocyclic carbene (tetra-NHC) ligands via in situ transmetalation is described. The ruthenium complexes show differing coordination geometries depending on the length of the alkyl linker. Replacement of the two cis acetonitrile ligands in the methylene bridged ruthenium complex by nucleophiles also influences the coordination geometry. Both structural motifs were evaluated in transfer hydrogenation (TH) of acetophenone, and in particular the sawhorse-type coordinated system exhibits remarkable activity with turnover frequencies of more than 100 000 h(-1).

Determination of the Stoichiometry, Stability Constant of Complexes Formation and Thermodynamic Parameters between 15-Crown-5, 1, 4, 8, 11-Tetrathiacyclotetradecane and 1, 7-Diaza-12-crown-4 Macrocyclic Ligands in Acetonitrile – Methanol Binary Solvent Mixtures

Determination of the Stoichiometry, Stability Constant of Complexes Formation and Thermodynamic Parameters between 15-Crown-5, 1, 4, 8, 11-Tetrathiacyclotetradecane and 1, 7-Diaza-12-crown-4 Macrocyclic Ligands in Acetonitrile – Methanol Binary Solvent Mixtures

A fluorescent carboxamide ligand, having combined ionophore/fluorophore moieties, exhibiting “On-Off” switching toward Zn2+ ion

A carboxamide ligand (N-(quinolin-8-yl)quinoline-2-carboxamide) (Hqcq) has been synthesized by a highly efficient procedure using the ionic liquid TBAB as an environmentally benign reaction medium. Selective “On-Off” switching behavior of the fluorescent ligand (Hqcq) in acetonitrile has been studied for Zn(II) ion. The Hqcq was weakly emissive in the absence of metal ions, but fluorescence intensity was increased significantly upon addition of two equivalent of Zn(II) ion. This enhancement was correlated to Zn(II) coordination of the qcq−, producing an efficient chelation-enhanced fluorescence (CHEF) effect. Other interfering elements such as Cd(II) and Hg(II), show either no or slight change in the fluorescence intensity under similar experimental conditions.

Preparation, Characterization and Antibacterial Studies of New 2-(naphthalene-2-yl)-2-(naphthalene-2ylamino) Acetonitrile Ligand with Some Metal Ions

In the present work, the synthesized of a series of metal ions complexes of [Cr(III), Fe(III), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II)] from new bidentate 2-(naphthalene-2-yl)-2-(naphthalene-2ylamino) acetonitrile ligand (L) which prepared from 2-naphthaldehyde and naphthalene-2-amine in the presence of KCN and alcoholic medium. These compounds were characterized by using several techniques FT-IR, UV-Visible spectrophotometer, magnetic susceptibility, thermal gravimetric analysis (TGA), elemental analysis, molar conductivity, 1H-NMR, as well as atomic absorption. From the spectral studies, an octahedral monomer structure was proposed for all complexes. The nature of the complexes formed in ethanolic solution has been studied following the molar ratio method and the result recorded [1:2] [M:L] ratio. Some complexes were found to be non-electrolyte and others were found to be weak electrolyte in ethanol. Biological activities of the free ligand and its metal complexes have been tested against a number of microorganisms in order to assess their antimicrobial properties.

The Effect of Hg(II) on the Optical Characteristics of Cycloiridated 2-Phenylbenzothiazole Complexes with Chelating Ligands Containing Sulfur Donor Atoms

The [Ir(bt)2(S^S)], [Ir(bt)2(S^N)], and [Ir(bt)2(CH3CN)2]PF6 complexes, where (bt)− is a deprotonated form of 2-phenylbenzothiazole and (S^S)− and (S^N)− are diethyldithiocarbamate, O-ethyldithiocarbonate, 2-mercaptobenzothiazolate, 2-mercaptobenzoxazolate, and 2-mercaptopyridinate ions, and the effect of Hg(II), Cu(II), Cd(II), and Zn(II) cations on the optical characteristics of these complexes are studied by electron absorption spectroscopy and emission spectroscopy. A hypsochromic shift of the absorption and phosphorescence bands of complexes in substituting the (S^S)− and (S^N)− chelating ligands with acetonitrile ligands is attributed to a lower energy of dIr orbitals compared with the mixed dIr/p(S) orbitals. It is shown that the presence of Hg(II) cations results in a hypsochromic shift of the absorption and phosphorescence bands of complexes [Ir(bt)2(S^S)] and [Ir(bt)2(S^N)] because of an effective reaction of substitution of chelating ligands to acetonitrile ligands.

Platinum complexes bearing normal and mesoionic N-heterocyclic carbene based pincer ligands: syntheses, structures, and photo-functional attributes.

Platinum complexes featuring pyridine bis-N-heterocyclic-imidazol-2-ylidene/-mesoionic-triazol-5-ylidene donors as pincer ligands and chloro (-Cl), acetonitrile (-NCCH3) or cyano (-CN) groups as auxiliary ligands are prepared as highly strained organometallic phosphors. X-ray structures of four of these complexes confirm a distorted square planar geometry, where the pincer ligand and its mesityl wingtips occur in a twisted conformation to each other. Electrochemical and photophysical characterization have been carried out and the experimental results are interpreted with the aid of density functional theory calculations. Emission responses of complexes under exposure to different vapors and mechanical shear are reported. Notably, the platinum complex featuring pyridine bis-imidazol-2-ylidene and a weakly donating acetonitrile auxiliary ligand exhibited strong aquachromic and mechanochromic emission responses, showing color changes from sky blue to green or yellow-green.

Influence of Copper Oxidation State on the Bonding and Electronic Structure of Cobalt-Copper Complexes.

Heterobimetallic complexes that pair cobalt and copper were synthesized and characterized by a suite of physical methods, including X-ray diffraction, X-ray anomalous scattering, cyclic voltammetry, magnetometry, electronic absorption spectroscopy, electron paramagnetic resonance, and quantum chemical methods. Both Cu(II) and Cu(I) reagents were independently added to a Co(II) metalloligand to provide (py3tren)CoCuCl (1-Cl) and (py3tren)CoCu(CH3CN) (2-CH3CN), respectively, where py3tren is the triply deprotonated form of N,N,N-tris(2-(2-pyridylamino)ethyl)amine. Complex 2-CH3CN can lose the acetonitrile ligand to generate a coordination polymer consistent with the formula "(py3tren)CoCu" (2). One-electron chemical oxidation of 2-CH3CN with AgOTf generated (py3tren)CoCuOTf (1-OTf). The Cu(II)/Cu(I) redox couple for 1-OTf and 2-CH3CN is reversible at -0.56 and -0.33 V vs Fc(+)/Fc, respectively. The copper oxidation state impacts the electronic structure of the heterobimetallic core, as well as the nature of the Co-Cu interaction. Quantum chemical calculations showed modest electron delocalization in the (CoCu)(+4) state via a Co-Cu σ bond that is weakened by partial population of the Co-Cu σ antibonding orbital. By contrast, no covalent Co-Cu bonding is predicted for the (CoCu)(+3) analogue, and the d-electrons are fully localized at individual metals.

Laser synthesis and spectroscopy of acetonitrile/silver nanoparticles

Silver nanoparticles with acetonitrile ligands are produced in a laser ablation flow reactor. Excimer laser ablation produces gas phase metal clusters which are thermalized with helium or argon collisions in the flowtube, and reactions with acetonitrile vapor coordinate this ligand to the particle surface. The gaseous mixture is captured in a cryogenic trap; warming produces a solution of excess ligand and coated particles. TEM images reveal particle sizes of 10–30nm diameter. UV–vis absorption and fluorescence spectra are compared to those of standard silver nanoparticles with surfactant coatings. Deep-UV ligand absorption is strongly enhanced by nanoparticle adsorption.

Crystal structure of di-μ-iodido-bis-[bis(aceto-nitrile-κN)copper(I)

The title compound, [Cu2I2(CH3CN)4], exhibits a centrosymmetric Cu2I2 core [Cu⋯Cu distance = 2.7482 (11) Å], the CuI atoms of which are further coordinated by four mol­ecules of aceto­nitrile. The CuI atom has an overall distorted tetra­hedral coordination environment evidenced by L—Cu—L angles (L = N or I) ranging from 100.47 (10) to 117.06 (2)°. The coordination geometries of the aceto­nitrile ligands deviate slightly from linearity as shown by Cu—N—C angles of 167.0 (2) and 172.7 (2)°. In the crystal, there are no significant hydrogen-bonding inter­actions present, so the crystal packing seems to be formed predominantly by van der Waals forces.

Synthesis and structures of ruthenium-NHC complexes and their catalysis in hydrogen transfer reaction.

Ruthenium complexes [Ru(L1)2(CH3CN)2](PF6)2 (1), [RuL1(CH3CN)4](PF6)2 (2) and [RuL2(CH3CN)3](PF6)2 (3) (L1= 3-methyl-1-(pyrimidine-2-yl)imidazolylidene, L2 = 1,3-bis(pyridin-2-ylmethyl)benzimidazolylidene) were obtained through a transmetallation reaction of the corresponding nickel–NHC complexes with [Ru(p-cymene)2Cl2]2 in refluxing acetonitrile solution. The crystal structures of three complexes determined by X-ray analyses show that the central Ru(II) atoms are coordinated by pyrimidine- or pyridine-functionalized N-heterocyclic carbene and acetonitrile ligands displaying the typical octahedral geometry. The reaction of [RuL1(CH3CN)4](PF6)2 with triphenylphosphine and 1,10-phenanthroline resulted in the substitution of one and two coordinated acetonitrile ligands and afforded [RuL1(PPh3)(CH3CN)3](PF6)2 (4) and [RuL1(phen)(CH3CN)2](PF6)2 (5), respectively. The molecular structures of the complexes 4 and 5 were also studied by X-ray diffraction analysis. These ruthenium complexes have proven to be efficient catalysts for transfer hydrogenation of various ketones.

Selective Photodissociation of Acetonitrile Ligands in Ruthenium Polypyridyl Complexes Studied by Density Functional Theory.

Metal complexes that release ligands upon photoexcitation are important tools for biological research and show great potential as highly specific therapeutics. Upon excitation with visible light, [Ru(TQA)(MeCN)2](2+) [TQA = tris(2-quinolinylmethyl)amine] exchanges one of the two acetonitriles (MeCNs), whereas [Ru(DPAbpy)MeCN](2+) [DPAbpy = N-(2,2'-bipyridin-6-yl)-N,N-bis(pyridin-2-ylmethyl)amine] does not release MeCN. Furthermore, [Ru(TQA)(MeCN)2](2+) is highly selective for release of the MeCN that is perpendicular to the plane of the two axial quinolines. Density functional theory calculations provide a clear explanation for the photodissociation behavior of these two complexes. Excitation by visible light and intersystem crossing leads to a six-coordinate (3)MLCT state. Dissociation of acetonitrile can occur after internal conversion to a dissociative (3)MC state, which has an occupied dσ* orbital that interacts in an antibonding fashion with acetonitrile. For [Ru(TQA)(MeCN)2](2+), the dissociative (3)MC state is lower than the (3)MLCT state. In contrast, the (3)MC state of [Ru(DPAbpy)MeCN](2+) that releases acetonitrile has an energy higher than that of the (3)MLCT state, indicating dissociation is unfavorable. These results are consistent with the experimental observations that efficient photodissociation of acetonitrile occurs for [Ru(TQA)(MeCN)2](2+) but not for [Ru(DPAbpy)MeCN](2+). For the release of the MeCN ligand in [Ru(TQA)(MeCN)2](2+) that is perpendicular to the axial quinoline rings, the (3)MLCT state has an occupied quinoline π* orbital that can interact with a dσ* Ru-NCCH3 antibonding orbital as the Ru-NCCH3 bond is stretched and the quinolines bend toward the departing acetonitrile. This reduces the barrier for the formation of the dissociative (3)MC state, leading to the selective photodissociation of this acetonitrile. By contrast, when the acetonitrile is in the plane of the quinolines or bpy, no interaction occurs between the ligand π* orbital and the dσ* Ru-NCCH3 orbital, resulting in high barriers for conversion to the corresponding (3)MC structures and no release of acetonitrile.

Synthesis and Electrochemical Properties of cis- and trans-[Mo2(O2C-Fc)2(DArF)2] (O2C-Fc = Ferrocenecarboxylate; DArF = N,N'-Diarylformamidinate).

The reaction of cis-[Mo2(O2C-Fc)2(NCCH3)4][BF4]2 (cis-1) with three electronically different N,N'-diarylformamidinate (DArF) ligands [DArF = N,N'-diphenylformamidinate (DPhF), N,N'-di(p-trifluoromethylphenyl)formamidinate (DTfmpF), and N,N'-di(p-anisyl)formamidinate (DAniF)] results in products of the general composition [Mo2(O2C-Fc)2(DArF)2]. Even though the trans-[Mo2(O2C-Fc)2(DArF)2] isomers were originally expected to be the sole products, the corresponding cis-[Mo2(O2C-Fc)2(DArF)2] complexes were isolated as well via crystallization and verified unambiguously by X-ray crystallography. All novel complexes, namely, cis-[Mo2(O2C-Fc)2(DPhF)2] (cis-2a), cis-[Mo2(O2C-Fc)2(DTfmpF)2] (cis-2b), and trans-[Mo2(O2C-Fc)2(DAniF)2] (trans-2c), were studied regarding their electrochemical properties with respect to electrolyte, solvent, and ligand. The electron-donating ligand DArF(-) enables the oxidation of the [Mo2](4+) unit prior to that of Fc, while the oxidation sequence is reversed when acetonitrile or diphosphine ligands are coordinated instead of formamidinate. In the case of trans-[Mo2(O2C-Fc)2(DAniF)2], interactions were found between the two redox-active ferrocenecarboxylate ligands, with a clear ΔE1/2 value originating from the peak-to-peak separation in DPV of around 100 mV with CH2Cl2 as solvent. Furthermore, the second oxidation of the Mo2-handle [Mo2](5+)/[Mo2](6+) was exclusively observed with DAniF(-) as the ligand. Similar absorption patterns in UV-vis spectra were found within the series 2a-2c, corresponding to similar structural and electronic features of the complexes.

Octahedral Chiral-at-Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions.

Octahedral iridium(III) complexes containing two bidentate cyclometalating 5-tert-butyl-2-phenylbenzoxazole (IrO) or 5-tert-butyl-2-phenylbenzothiazole (IrS) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5-5.0 mol % catalyst loading) for a variety of reactions with α,β-unsaturated carbonyl compounds, namely Friedel-Crafts alkylations (94-99% ee), Michael additions with CH-acidic compounds (81-97% ee), and a variety of cycloadditions (92-99% ee with high d.r.). Mechanistic investigations and crystal structures of an iridium-coordinated substrates and iridium-coordinated products are consistent with a mechanistic picture in which the α,β-unsaturated carbonyl compounds are activated by two-point binding (bidentate coordination) to the chiral Lewis acid.

Synthesis and characterization of an iron complex bearing a cyclic tetra-N-heterocyclic carbene ligand: an artifical heme analogue?

An iron(II) complex with a cyclic tetradentate ligand containing four N-heterocyclic carbenes was synthesized and characterized by means of NMR and IR spectroscopies, as well as by single-crystal X-ray structure analysis. The iron center exhibits an octahedral coordination geometry with two acetonitrile ligands in axial positions, showing structural analogies with porphyrine-ligated iron complexes. The acetonitrile ligands can readily be substituted by other ligands, for instance, dimethyl sulfoxide, carbon monoxide, and nitric oxide. Cyclic voltammetry was used to examine the electronic properties of the synthesized compounds.