Effects of Different Solvent Characteristics on the Proton-Ligand and Ni2+-, Sm3+-, AND Yb3+- Ligand Formation Constants of 5,5-Dimethyl-Cyclohexane-2-(2-Hydroxyphenyl)Hydrazono- 1,3-Dione (DCPHD) in Various Mixed Aqueous Solvents-(II)

Complex equilibria of DCPHD with proton and Ni²⁺, Sm³⁺, and Yb³⁺ ions has been measured in various mixed aqueous solvents, viz: isopropanol-water, acetone-water, ethanol-water, and methanol-water. Based on potentiometric equilibrium measurements of hydrogen ion concentration at 30°C, ionic strenght 0.10 M (KNO₃) and in the above various mixed aqueous solvents, the values of the protonation constants of DCPHD and the stability constants of DCPHD with Ni²⁺, Sm³⁺, and Yb³⁺ have been evaluated. The variation of protonation and stability constants with the inverse of dielectric constant or mole fraction of the solvent was studied. Application of Fuoss expression and consideration of electrosatic and non-electrostatic effects are made to explain the values of the constants.     

ACE applied to the quantitative characterization of benzo‐18‐crown‐6‐ether binding with alkali metal ions in a methanol–water solvent system

ACE was applied to the quantitative evaluation of noncovalent binding interactions between benzo‐18‐crown‐6‐ether (B18C6) and several alkali metal ions, Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺, in a mixed binary solvent system, methanol–water (50/50 v/v). The apparent binding (stability) constants (K_b) of B18C6–alkali metal ion complexes in the hydro‐organic medium above were determined from the dependence of the effective electrophoretic mobility of B18C6 on the concentration of alkali metal ions in the BGE using a nonlinear regression analysis. Before regression analysis, the mobilities measured by ACE at ambient temperature and variable ionic strength of the BGE were corrected by a new procedure to the reference temperature, 25°C, and the constant ionic strength, 10 mM . In the 50% v/v methanol–water solvent system, like in pure methanol, B18C6 formed the strongest complex with potassium ion (log K_b=2.89±0.17), the weakest complex with cesium ion (log K_b=2.04±0.20), and no complexation was observed between B18C6 and the lithium ion. In the mixed methanol–water solvent system, the binding constants of the complexes above were found to be about two orders lower than in methanol and about one order higher than in water.     

Solvent effects on complexation of thallium(I) with guanosine 5′‐monophosphate in methanol–water mixtures

The interaction of guanosine 5′‐monophosphate, GMP, with the thallium(I) ion was studied by UV–vis and potentiometric titration methods and ³¹P NMR spectroscopy. Both NMR spectra and UV–vis titration data have shown that GMP coordinates via guanine to the thallium(I) ion in the pH range 1.5–10. Our study of the system Tl(I) + GMP was performed in water–methanol mixtures with different volume ratios of methanol. The complexation equilibrium in the pH range of study led to the following mononuclear species: TlH₂(GMP)⁺, TlH(GMP) and Tl(GMP)^?, where (GMP)^2? represents the fully dissociated ligand. The formation constants of the species were calculated in the various media at constant temperature (25 °C) and constant ionic strength of sodium perchlorate (0.1 mol dm^?3) using a suitable computer program. The formation constants were analyzed in terms of Kamlet and Taft's parameters. A single‐parameter correlation of the formation constants, β₁₂₁, β₁₁₁ and β₁₀₁ vs α (hydrogen‐bond donor acidity), β (hydrogen‐bond acceptor basicity) and for π* (dipolarity/polarizability) are relatively poor in all solutions, but multi‐parameter correlations represent significant improvements with regard to the single‐parameter model. In this work, we have also used the normalized polarity parameter, E_T^N, alone and in combination with some of the Kamlet–Taft parameters to find a better correlation of the formation constants in different methanol–water mixtures. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis,Spectral, X‐Ray Diffraction,DFT, and Nematicidal Activity of Mixed Ligand Complexes of Ethyl 2‐(2‐Hydroxybenzylidine)‐Hydrazine Carboxylate and 1,10‐Phenanthroline with Some Transition Metals

In this work, mixed ligand complexes derived from ethyl 2‐(2‐hydroxybenzylidine)‐hydrazine carboxylate (HL) and 1,10‐phenanthroline (Phen) as ligands were synthesized and their structures elucidated by elemental analysis, infrared (IR), electronic,¹H NMR, and mass spectra, X‐ray diffraction (XRD), magnetic susceptibility measurements, and TG/DTG analyses. The analytical and spectral data support the formation of the complexes with the central ion in each complex six‐coordinated and a slightly distorted octahedral geometry. The IR spectra showed that HL and Phen ligands act as neutral bidentates. The XRD patterns of the complexes showed their crystalline nature. The calculated bond length and the force constant F (U═O) in the uranyl complex are 1.738 Å and 685.90 Nm⁻¹, respectively. The molar conductance values of the synthetic complexes in DMF were found to be in the range 5.00–274.06 S cm²/mol at room temperature. The thermodynamic parameters were evaluated by using the Coats–Redfern (CR) and Horowitz–Metzeger (HM) methods. Theoretical molecular structures were investigated by the density functional theory/B3LYP method using the Gaussian 98 W basis set. The nematicidal activity of the ligands and its metal complexes was also studied.     

The σ‐Aromatic Clusters [Zn3]+ and [Zn2Cu]: Embryonic Brass

The triangular clusters [Zn₃Cp*₃]⁺ and [Zn₂CuCp*₃] were obtained by addition of the in situ generated, electrophilic, and isolobal species [ZnCp*]⁺ and [CuCp*] to Carmona’s compound, [Cp*Zn? ZnCp*], without splitting the Zn? Zn bond. The choice of non‐coordinating fluoroaromatic solvents was crucial. The bonding situations of the all‐hydrocarbon‐ligand‐protected clusters were investigated by quantum chemical calculations revealing a high degree of σ‐aromaticity similar to the triatomic hydrogen ion [H₃]⁺. The new species serve as molecular building units of Cu_nZn_m nanobrass clusters as indicated by LIFDI mass spectrometry.     

9Be and 31P NMR analyses on the influence of imino groups on Be2+ complex stabilities of a series of cyclo‐μ‐imido triphosphate anions

The complexation behaviors of Be²⁺ with cyclo‐μ‐imido triphosphate anions, cP₃O_9?n(NH)_n^3? (n = 1, 2), have been investigated by both ⁹Be and ³¹P NMR techniques at ?2.3 °C in order to clarify the coordination structures of the complexes. The spectra showed that cP₃O_9?n(NH)_n (n = 1, 2) ligands form ML, ML₂, and M₂L complexes with Be²⁺ ions, and the formation of complexes coordinating with nitrogen atoms of the cyclic framework in the ligand molecule has been excluded. These complexation trends are very similar to those of Be²⁺‐cP₃O₆(NH)₃^3? system, which has been reported by us. The peak deconvolution of ⁹Be NMR spectra made these beryllium complexes amenable to stability constant determinations. The stability constants of the complexes increase with an increase in the protonation constants of the ligands as the number of imino groups, which constitute the ligand molecules, is ascended. This increase is primarily attributable to the lower electronegativity of nitrogen atoms than oxygen atoms, which are directly bonded to central phosphorus atoms; moreover, tautomerism equilibrium in the entire of the imidopolyphosphate molecule is also responsible to the higher basicity. ³¹P NMR spectra measured concurrently have verified the formation of the complexes estimated by the ⁹Be NMR measurement. Intrinsic ³¹P NMR chemical shift values of the phosphorus atoms belonging to ligand molecules complexed with Be²⁺ cations have been determined. Not only the protonation constants but also the stability constants of all Be²⁺ complexes increase approximately linearly with an increase in the number of imino groups. Copyright © 2013 John Wiley & Sons, Ltd.     

Protonation Behaviour of Chiral Tetradentate Polypyridines Derived from α‐Pinene

Detailed protonation experiments of the [5,6]‐pinenebipyridine molecule and the unsubstituted [4,5]‐ and [5,6]‐CHIRAGEN[0] ligands in various solvents indicate a variety of structures of the protonated species. UV‐visible and NMR measurements (including ¹⁵N chemical shifts) show the transition from trans to cis conformation of [5,6]‐pinenebipyridine upon protonation. The [4,5]‐CHIRAGEN[0] ligand, in which the protonation sites of the nitrogen atom donors are at opposite sides of the molecule, behave essentially like two independent bipyridine moieties; this behaviour was monitored by UV‐visible, CD and NMR spectroscopy (including ¹⁵N data). In the case of the [5,6]‐CHIRAGEN[0], a pocket of donor atoms provides a chiral environment for two protons per ligand.     

Synthesis and Optical Properties of 2,13‐Dibenzothiazol‐2′‐yldibenzo[b,k]‐18‐crown‐6

A new crown ether of 2,13‐dibenzothiazol‐2′‐yldibenzo[b,k]‐18‐crown‐6 was synthesized from 2,13‐diformyl‐ dibenzo[b,k]‐18‐crown‐6 with 2‐aminothiophenol. The binding behavior and the optical properties of the crown ether were examined through UV‐visible spectroscopy and fluorescence spectroscopy. When complexed with Na⁺, K⁺, Rb⁺ and Cs⁺ ions, it led to intramolecular charge transfer and caused the changes of the fluorescence spectra. The protonation of the crown ether was also studied.     

Lanthanide(III) Complexes of 2‐[4,7,10‐Tris(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecan‐1‐yl]acetic Acid (H7DOA3P): Multinuclear‐NMR and Kinetic Studies

The protonation constants of 2‐[4,7,10‐tris(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecan‐1‐yl]acetic acid (H₇DOA3P) and of the complexes [Ln(DOA3P)]^4? (Ln=Ce, Pr, Sm, Eu, and Yb) have been determined by multinuclear NMR spectroscopy in the range pD 2–13.8, without control of ionic strength. Seven out of eleven protonation steps were detected (pK =13.66, 12.11, 7.19, 6.15, 5.77, 2.99, and 1.99), and the values found compare well with the ones recently determined by potentiometry for H₇DOA3P, and for other related ligands. The overall basicity of H₇DOA3P is higher than that of H₄DOTA and trans‐H₆DO2A2P but lower than that of H₈DOTP. Based on multinuclear‐NMR spectroscopy, the protonation sequence for H₇DOA3P was also tentatively assigned. Three protonation constants (pK_MHL, pK_MH2L, and pK_MH3L) were determined for the lanthanide complexes, and the values found are relatively high, although lower than the protonation constants of the related ligand (pK , pK , and pK ), indicating that the coordinated phosphonate groups in these complexes are protonated. The acid‐assisted dissociation of [Ln(DOA3P)]^4? (Ln=Ce, Eu), in the region c_H+=0.05–3.00 mol dm^?3 and at different temperatures (25–60°), indicated that they have slightly the same kinetic inertness, being the [Eu(H₂O)₉]³⁺ aqua ion the final product for europium. The rates of complex formation for [Ln(DOA3P)]^4? (Ln=Ce, Eu) were studied by UV/VIS spectroscopy in the pH range 5.6–6.8. The reaction intermediate [Eu(DOA3P)]* as ‘out‐of‐cage’ complex contains four H₂O molecules, while the final product, [Eu(DOA3P)]^4?, does not contain any H₂O molecule, as proved by steady‐state/time‐resolved luminescence spectroscopy.     

Zur Elektronenstruktur hochsymmetrischer Verbindungen der f‐Elemente. 38 [1] Kristall‐, Molekül‐ und Elektronenstruktur von Tris(hydrotris(1‐pyrazolyl)borato)‐samarium(III)

Electronic Structures of Highly Symmetrical Compounds of f Elements. 38 [1] Crystal, Molecular and Electronic Structure of Tris(hydrotris(1‐pyrazolyl)borato)samarium(III) Tris(hydrotris(1‐pyrazolyl)borato)samarium(III) (SmTp₃) crystallizes in the space group P6₃/m (No. 176) with two molecules in the unit cell. The Sm³⁺ central ion is coordinated by nine N atoms in the shape of a tricapped trigonal prism, leading to an effective crystal field (CF) of D_3h symmetry. The underlying CF splitting pattern was extracted from the absorption and luminescence spectra run at room and low temperatures, and simulated by fitting the free parameters of a phenomenological Hamiltonian achieving an r.m.s. deviation of 9.4 cm^?1 for 58 assignments. The parameters used allow the estimation of the global ligand field strength experienced by the Sm³⁺ central ion, the insertion of SmTp₃ into empirical nephelauxetic and relativistic nephelauxetic series, and the set‐up of experimentally based nonrelativistic and relativistic molecular orbital schemes in the f range.     

A novel one‐dimensional complex: catena‐poly­[[manganese(III)‐di‐μ‐2‐[(2‐hydroxy­ethyl)­imino­methyl]­phenolato‐κ2O1,N:κO2;κO2:κ2O1] chloride]

In the title one‐dimensional complex, {[Mn^III(C₉H₁₀NO₂)₂]Cl}_n, the Schiff base ligand 2‐[(2‐hydroxy­ethyl)­imino­methyl]­phenolate (Hsae⁻) functions as both a bridging and a chelating ligand. The Mn^III ion is six‐coordinated by two N and four O atoms from four different Hsae⁻ ligands, yielding a distorted MnO₄N₂ octahedral environment. Each [Mn^III(Hsae)₂]⁺ cationic unit has the Mn atom on an inversion centre and each [Mn^III(Hsae)₂]⁺ cation lies about another inversion centre. The chain‐like complex is further extended into a three‐dimensional network structure through Cl⋯H—O hydrogen bonds and C—H⋯π contacts involving the Hsae⁻ rings.     

NMR study of the coordinating behavior of 2,6‐bis(benzimidazol‐2′‐yl)pyridine

The coordination sites of 2,6‐bis(benzimidazol‐2′‐yl)pyridine ( 1 ) toward protons and the diamagnetic metal ions Li⁺, Na⁺, and Co³⁺ were investigated by NMR spectroscopy. Variable temperature ¹H and ¹³C NMR experiments were performed on 1 in order to evaluate the tautomeric equilibrium and hydrogen bonding. Imidazole dicoordinated aromatic nitrogen atoms were protonated by trichloroacetic acid and the three N‐dicoordinated atoms by fuming H₂SO₄. Reactions of the ligand 1 and benzimidazole 2 with metallic sodium or LiH afforded anionic species; the alkali metal ions appeared solvated by THF, but not by the ligands 1 or 2 . In contrast, reaction of 1 with Co(III) produces the stable cation [Co( 1 ‐H)₂]⁺ with cobalt ion coordinated by two molecules of the monodeprotonated ligand. © 2000 John Wiley & Sons, Inc. Heteroatom Chem 11:392–398, 2000     

A Dissociative Route to C?H Bond Activation: Ligand Cyclometalation in cis‐Dimethyl[(sulfinyl‐κS)bis[methane]][tris(2‐methylphenyl)phosphine]platinum(2+)

The dialkyl compound cis‐dimethyl[(sulfinyl‐κS)bis[methane]][tris(2‐methylphenyl)phosphine]platinum(2+) (cis‐[Pt(Me)₂(dmso)(P(o‐tol)₃]; 1 ) has been isolated from the reaction of cis‐dimethylbis[(sulfinyl‐κS)bis[methane]]platinum(2+) (cis‐[Pt(Me)₂(dmso)₂]) with tris(2‐methylphenyl)phosphane (P(o‐tol)₃). Restricted rotation around the P? C_ipso bonds of the phosphane ligand generates two different conformers, 1a and 1b , in rapid exchange in non‐polar solvents at low temperature. Strong through‐space contacts between the ortho‐Me substituent groups on the ligand and the cis‐Me groups in the coordination plane were determined, which proved useful for identifying the atropisomers formed. At room temperature, ¹H‐NMR spectra of 1 maintain a ‘static’ pattern upon onset of easy and rapid ortho‐platination, leading to [[2‐[bis(2‐methylphenyl)phosphino‐κP]phenyl]methyl‐κC]methyl[(sulfinyl‐κS)bis[methane]]platinum(2+) ( 2 ), a new C,P‐cyclometalated compound of platinum(II), with liberation of methane. The process has been studied by ¹H‐ and ³¹P{¹H}‐NMR in CDCl₃, and kinetics experiments were performed by conventional spectrophotometric techniques. The first‐order rate constants k_c decrease with the addition of dimethyl sulfoxide until the process is blocked by the presence of a sufficient excess of sulfoxide. This behavior reveals a mechanism initiated by ligand dissociation and formation of a three‐coordinate species. The value of the rate constant for dimethyl sulfoxide dissociation k₁ has been measured independently over a wide temperature range by both ¹H‐NMR ligand exchange (isotopic labeling experiments) and ligand substitution (stopped‐flow pyridine for dimethyl sulfoxide substitution). The rates of the two processes are in reasonable agreement at the same temperature, and a single Eyring plot can be constructed with the two sets of kinetics data. However, the value of the derived dissociation constant at 308 K (k₁=6.5±0.3 s^?1) is at least two orders of magnitude higher than that of cyclometalation (k_c=0.0098±0.0009 s^?1 at 308 K). Clearly, the dissociation step is not rate‐determining for cyclometalation. A multistep mechanism consistent with mass‐law retardation is derived, which involves a pre‐equilibrium that controls the concentration of an unsaturated three‐coordinate, 14‐electron T‐shaped cis‐[PtMe₂{P(o‐tol)₃}] intermediate. Cyclometalation is initiated in this latter by an agostic interaction with the σ(C? H) orbital of a methyl group. Oxidative addition of the C? H bond follows, yielding a cyclometalated‐hydrido 16‐electron Pt(IV) five‐coordinate intermediate. Finally, reductive elimination and re‐entry of dimethyl sulfoxide with liberation of methane should yield the cyclometalated species 2 .     

The influence of medium on stability of coordination compounds: I. The system Cu(SCN)+-NaNO3-C2H5OH-H2O

The stability constants of Cu(SCN)⁺ in the titled system have been determined by spectro-photometric measurements at 25°C for 0, 5, 10, 15, 20 and 25 wt% of ethyl alcohol in mixed solvents. The total ionic strength of the solution are 0.2-2.0 mol·dm^?3 and pH 1.5-1.6. On basis of Pitzer's theory, a method of determining thermodynamic stability constants of coordination compounds in mixed solvents by curve fitting technique have been proposed. The stability constants of Cu(SCN)⁺ in mixed solvents have been correlated with composition and dielectric constant of the solvent mixture.     

Potentiometric and Theoretical Studies of (2Z, 3Z)-2H-benzo[b][1,4]thiazine-2,3(4H)-dionedioxime with Some Divalent Transition Metal Ions

The protonation equilibria of (2Z, 3Z)-2H-benzo[b][1,4]thiazine-2,3(4H)-dionedioxime (BTDH₂) together with the equilibria of its bis- binary complexes of Co(II), Ni(II), Cu(II) and Zn(II) were investigated potentiometrically. The investigation was carried out at 25 ± 0.1 °C, in aqueous solution, with a constant ionic strength of 0.100 mol·dm^?3 NaCl. The protonation constants of the ligand together with the stability constants of a variety of complexes were determined potentiometrically in 10 % ethanol–water mixed solution using the SUPERQUAD computer program. Theoretical calculations were set up to assist in understanding the protonation sequence in the ligand molecule via the semi-empirical molecule orbital method of parameterized model number 3. Results are discussed in connection to the basicity of the donor atoms and structural arrangement of the ligand. Although BTDH₂ has two dissociable protons, four protonation constants can be measured under the experimental conditions presented. These four protonation constants (as log₁₀ βs) are 10.245, 19.397, 22.414 and 25.176.     

A Spectrophotometric Investigation of the Interaction of Iodine with Dibenzyldiaza‐18‐crown‐6, Aza‐15‐crown‐5 and N‐phenylaza‐15‐crown‐5 in Chloroform Solution

The complex formation reactions between iodine and DBzDA18C6, A15C5 and N‐phenylA15C5 have been studied spectrophotometrically in chloroform solution. In the case of DBzDA18C6 is the resulting 1:2 (ligand…I⁺)I₃^?, while, in the case of A15C5 and N‐phenylA15C5 a 2:2 molecular complex of [(ligand)₂…I⁺]I₃^? type was formed. The spectrophotometric results indicate that gradual release of triiodide ion from its contact ion paired form in the molecular complex into the solution is the rate‐determining step of the reaction. The kinetic rate constants for the complexation reactions were determined at different temperatures, and activation parameters were calculated from Arrhenius and Eyring equations.     

Synthesis,NMR characterization and ab initio 6‐31G* study of 1‐aryl‐2,3‐dialkyl‐1,4,5,6‐tetrahydropyrimidinium salts

We describe the synthesis of a series of 1‐aryl‐2,3‐dialkyl‐1,4,5,6‐tetrahydropyrimidinium salts 1 , by alkylation of the corresponding 1,4,5,6‐tetrahydropyrimidines 2 . We analyze the changes in the ¹H and ¹³C NMR spectra of compounds 2 induced by protonation and quaternization. The results of an ab initio theoretical study on amidine 2a , and the cations resulting from its protonation ( 2aH ⁺) and quaternization ( la ⁺) are presented. A qualitative correlation was found between ¹³C NMR and theoretical data in the case of protonation. The influence of the substitution patterns in the ¹H and ¹³C NMR spectra of compounds 1 is also discussed.     

Ligand Design for Site‐Selective Metal Coordination: Synthesis of Transition‐Metal Complexes with η6‐Coordination of the Central Ring of Anthracene

A polycyclic aromatic ligand for site‐selective metal coordination was designed by using DFT calculations. The computational prediction was confirmed by experiments: 2,3,6,7‐tetramethoxy‐9,10‐dimethylanthracene initially reacts with [(C₅H₅)Ru(MeCN)₃]BF₄ to give the kinetic product with a [(C₅H₅)Ru]⁺ fragment coordinated at the terminal ring, which is then transformed into the thermodynamic product with coordination through the central ring. These isomeric complexes have markedly different UV/Vis spectra, which was explained by analysis of the frontier orbitals. At the same time, the calculations suggest that electrostatic interactions are mainly responsible for the site selectivity of the coordination.     

Electrochemical and Theoretical Investigations of the Role of the Appended Base on the Reduction of Protons by [Fe2(CO)4(κ2‐PNPR)(μ‐S(CH2)3S] (PNPR={Ph2PCH2}2NR,R=Me,Ph)

The behavior of [Fe₂(CO)₄(κ²‐PNP^R)(μ‐pdt)] (PNP^R=(Ph₂PCH₂)₂NR, R=Me ( 1 ), Ph ( 2 ); pdt=S(CH₂)₃S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP^R appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF₃SO₃H or CH₃SO₃H; the cation with a bridging hydride ligand, 1 μH⁺ (R=Me) or 2 μH⁺ (R=Ph) is obtained rapidly. Only 1 μH⁺ can be protonated at the nitrogen atom of the PNP chelate by HBF₄?Et₂O or CF₃SO₃H, which results in a positive shift of the proton reduction by approximately 0.15 V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η²‐H₂ species in the Fe^IFe^II state. When R=Ph, the bridging hydride cation 2 μH⁺ cannot be protonated at the amine function by HBF₄?Et₂O or CF₃SO₃H, and protonation at the N atom of the one‐electron reduced analogue is also less favored than that of a S atom of the partially de‐coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2 μH⁺ . The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 (k_obs≈4–7 s^?1) because of the slow intramolecular proton migration and H₂ release steps identified by the theoretical study.     

Studies on the Mass Spectra of N‐Aryl α,β‐Unsaturated γ‐Lactams

The mass spectra of a series of N‐aryl α,β‐unsaturated γ‐lactams were studied. Besides the molecular ion, the three characteristic fragments such as [M⁺‐29], [M⁺‐55], and [M⁺‐82] were commonly found in a series of N‐Aryl α,β‐unsaturated γ‐lactams in EI/MS. Further more the mechanism for the interpretation of these fragments is also de scribed.