Kinetics and mechanism of platinum-thallium bond formation: the binuclear [(CN)5Pt-Tl(CN)](-) and the trinuclear [(CN)5Pt-Tl-Pt(CN)5](3-) complex

Formation kinetics of the metal-metal bonded binuclear [(CN)(5)Pt-Tl(CN)](-) (1) and the trinuclear [(CN)(5)Pt-Tl-Pt(CN)(5)](3-) (2) complexes is studied, using the standard mix-and-measure spectrophotometric method. The overall reactions are Pt(CN)(4)(2-) + Tl(CN)(2)(+) <==> 1 and Pt(CN)(4)(2-) + [(CN)(5)Pt-Tl(CN)](-) <==> 2. The corresponding expressions for the pseudo-first-order rate constants are k(obs) = (k(1)[Tl(CN)(2)(+)] + k(-1))[Tl(CN)(2)(+)] (at Tl(CN)(2)(+) excess) and k(obs) = (k(2b)[Pt(CN)(4)(2-)] + k(-2b))[HCN] (at Pt(CN)(4)(2-) excess), and the computed parameters are k(1) = 1.04 +/- 0.02 M(-2) s(-1), k(-1) = k(1)/K(1) = 7 x 10(-5) M(-1) s(-1) and k(2b) = 0.45 +/- 0.04 M(-2) s(-1), K(2b) = 26 +/- 6 M(-1), k(-2b) = k(2b)/K(2b) = 0.017 M(-1) s(-1), respectively. Detailed kinetic models are proposed to rationalize the rate laws. Two important steps need to occur during the complex formation in both cases: (i) metal-metal bond formation and (ii) the coordination of the fifth cyanide to the platinum site in a nucleophilic addition. The main difference in the formation kinetics of the complexes is the nature of the cyanide donor in step ii. In the formation of [(CN)(5)Pt-Tl(CN)](-), Tl(CN)(2)(+) is the source of the cyanide ligand, while HCN is the cyanide donating agent in the formation of the trinuclear species. The combination of the results with previous data predict the following reactivity order for the nucleophilic agents: CN(-) > Tl(CN)(2)(+) > HCN.     

Al(CN)6(3-) and Al(NC)6(3-) trianions

At this time the smallest trianions observed in the gas phase are fluorinated fullerenes and large organic ring systems with attached sulfonic acid groups. Considerably smaller trianions have been predicted to be sufficiently stable for observation in mass spectrometers, but have not yet been detected. Here two isomers of the aluminium cyanide trianion, Al(CN)(6)(3-) and Al(NC)(6)(3-), are studied using ab initio methods. These two isomers are predicted to be electronically stable and to show substantial barriers with respect to dissociation of CN(-) units. Thus, the investigated trianions hit a sweat-spot regarding the possibility of detection, as they are by far more robust with respect to dissociation than alkali halide trianions, while at the same time materials from which these trianions can at least in principle be formed are much more readily available than those needed for producing small covalently bound trianions.     

Solvent dependence of absorption and emission spectra of Ru(bpy)2(CN)2: experiment and explanation based on electronic structure theory

Measurements in acidic media and time-dependent density functional theory and DeltaSCF calculations were performed for Ru(bpy)2(CN)2 in 11 solvents of varying polarity to determine the solvent's influence on the absorption and emission spectra of the complex. The solvent effect caused by both the polarizable continuum nature of the solvent (characterized by the polarizable conductor model), and by the coordination of the cyano groups of the complex by solvent molecules were investigated. Both the absorption and emission maxima show a strong blue shift as the solute-solvent interaction increases, the magnitude of which is in good linear correlation with Gutmann's acceptor number of the solvent. The calculations reproduce the location, shape, and shift of the experimental metal-to-ligand charge transfer bands. The solvent shift is shown to be in good correlation with the charge difference between the Ru atom and the bpy ligand, which in turn is closely related to the HOMO energy. The coordination of the solvent molecule to the cyano group causes a smaller blue shift than the polarizable continuum solvent. The specific solute-solvent interaction becomes dominant, however, when the pH in a protic solvent is small and the complex is protonated.     

The Analogy between O and C(CN)2

The compounds of oxygen, i.e. OH acids, ethers, quinones, aldehydes, ketones, carboxylic esters and amine oxides, sulfoxides, and phosphane oxides, are compared and contrasted with those compounds which contain a C(CN)₂ moiety in place of the characteristic O atom. In their typical properties the pairs of analogs frequently display surprising agreement. The purpose of such analogy studies lies primarily in the estimation of reactivities; their limits are reached where specific properties of the structual components become effective.     

Density functional theory study of Te(CN)2, Te(CN)(NC), and Te(NC)2 and their isomerizations

The equilibrium structures of Te(CN)₂, Te(CN)(NC), and Te(NC)₂ and three isomerization reactions: Te(CN)₂ ? Te(CN)(NC), Te(CN)(NC) ? Te(NC)₂, and Te(CN)₂ ? Te(NC)₂ were studied in the gas-phase using density functional theory. Three functionals (B3LYP, BLYP, and BHLYP) were employed to characterize the low-lying electronic singlet and triplet TeC₂N₂ isomers. The basis sets for carbon and nitrogen used were of double-ζ plus polarization quality with additional s- and p-type diffuse functions, DZP++. For the tellurium atom, the LANL2DZ (ECP) basis set was used. The energetic ordering (kcal mol^?1) (B3LYP) including zero-point vibrational energy corrections for the singlet ground state isomers follows: Te(CN)₂ (0.0, global minimum) < Te(CN)(NC) (15.4) < Te(NC)₂ (29.8). Electrostatic potentials and average local ionization energies of the ground state Te(CN)₂, Te(CN)(NC), and Te(NC)₂ isomers provide some guidance as to sites for noncovalent and covalent interactions. Energetics such as the different forms of electron affinities, ionization energies, and singlet–triplet gaps were also reported. Further the theoretical rate constants for the isomerization reactions were evaluated using transition state theory. We predict that these isomers may crystallize in similar patterns, if stable, as does Se(CN)₂.     

TcI(CN)3(CO)3]2- and [ReI(CN)3(CO)3]2- :case studies for the binding properties of CN- and CO

The cyano carbonyl complexes [(99)Tc(CN)(3)(CO)(3)]2- and [Re(CN)(3)(CO)(3)]2- were synthesized and fully characterized. These complexes are additional members of the well-known d(6) transition metal complex series [M(CN)(3)(CO)(3)](n-). The analytical data obtained in this study thus offer a unique opportunity to study similarities and differences of cyanide and carbonyl binding in transition metal complexes.     

The electronic structure and spectrum of Mo(CN)8(3-)

State of the art CASSCF and CASPT2 calculations have been performed to elucidate the nature of the electronic transitions observed in the experimental spectrum of the octacyanomolybdate(V) cation. Assuming a triangular dodecahedral structure for this complex gives a convincing agreement between theory and experiment. All absorption bands are assigned to low-lying charge-transfer transitions involving excitations from ligand orbitals to 4dx2-y2. The calculated molecular orbitals reveal weak pi interactions between the metal and ligand orbitals, compared to much stronger sigma interactions. This calculated electronic structure substantiates the previous hypothesis concerning the giant spin ground states of magnetic clusters and networks containing Mo(CN)8(3-) as a constituent part.     

Stereocontrolled (3+2) cycloadditions between azomethine ylides and dipolarophiles: a fruitful interplay between theory and experiment

In this article we present recent developments in (3+2) cycloadditions with special emphasis on 1,3-dipolar reactions involving azomethine ylides and alkenes possessing electron withdrawing groups. It is found that there is not a general mechanism for these reactions since both concerted aromatic [(π)4(s)+(π)2(s)] mechanisms and stepwise processes involving zwitterionic intermediates can be found. These computational models can be extended to analyse the role of chiral catalysts in these reactions in order to understand the nature of the catalytic cycle and the origins of chiral induction.     

Electronic structure and molecular properties of the heptacyanorhenate [Re(CN)7]3- and [Re(CN)7]4- complexes

We report scalar relativistic and Dirac scattered wave (DSW) calculations on the heptacyanorhenate [Re(CN)7](3-) and Re(CN)7(4-) complexes. Both the ground and lowest excited states of each complex split by spin-orbit interaction by about 0.3 eV. The calculated molecular electronegativities chi indicate that the open-shell complex is less reactive than the closed-shell complex, in agreement with experimental observations. The calculations indicate that the ground state spin density is highly anisotropic and that spin-orbit effects are responsible for the magnetic anisotropy of the molecular g tensor of the Re(CN)7(3-) complex. The calculated optical electronic transitions for both complexes with a polarizable continuum model using a time-dependent density functional (TDDFT)/B3LYP formalism are in reasonable agreement with those observed in the absorption spectrum.     

Direct oxidation of L-cysteine by [FeIII(bpy)2(CN)2]+ and [FeIII(bpy)(CN)4]-

The oxidation of L-cysteine by the outer-sphere oxidants [Fe(bpy)2(CN)2]+ and [Fe(bpy)(CN)4]- in anaerobic aqueous solution is highly susceptible to catalysis by trace amounts of copper ions. This copper catalysis is effectively inhibited with the addition of 1.0 mM dipicolinic acid for the reduction of [Fe(bpy)2(CN)2]+ and is completely suppressed with the addition of 5.0 mM EDTA (pH<9.00), 10.0 mM EDTA (9.010.0) for the reduction of [Fe(bpy)(CN)4]-. 1H NMR and UV-vis spectra show that the products of the direct (uncatalyzed) reactions are the corresponding Fe(II) complexes and, when no radical scavengers are present, L-cystine, both being formed quantitatively. The two reactions display mild kinetic inhibition by Fe(II), and the inhibition can be suppressed by the free radical scavenger PBN (N-tert-butyl-alpha-phenylnitrone). At 25 degrees C and micro=0.1 M and under conditions where inhibition by Fe(II) is insignificant, the general rate law is -d[Fe(III)]/dt=k[cysteine]tot[Fe(III)], with k={k2Ka1[H+]2+k3Ka1Ka2[H+]+k4Ka1Ka2Ka3{/}[H+]3+Ka1[H+]2+Ka1Ka2[H+]+Ka1Ka2Ka3}, where Ka1, Ka2, and Ka3 are the successive acid dissociation constants of HSCH2CH(NH3+)CO2H. For [Fe(bpy)2(CN)2]+, the kinetics over the pH range of 3-7.9 yields k2=3.4+/-0.6 M(-1) s(-1) and k3=(1.18+/-0.02)x10(6) M(-1) s(-1) (k4 is insignificant in the fitting). For [Fe(bpy)(CN)4]- over the pH range of 6.1-11.9, the rate constants are k3=(2.13+/-0.08)x10(3) M(-1) s(-1) and k4=(1.01+/-0.06)x10(4) M(-1) s(-1) (k2 is insignificant in the fitting). All three terms in the rate law are assigned to rate-limiting electron-transfer reactions in which various thiolate forms of cysteine are reactive. Applying Marcus theory, the self-exchange rate constant of the *SCH2CH(NH2)CO2-/-SCH2CH(NH2)CO2- redox couple was obtained from the oxidation of L-cysteine by [Fe(bpy)(CN)4]-, with k11=4x10(5) M(-1) s(-1). The self-exchange rate constant of the *SCH2CH(NH3+)CO2-/-SCH2CH(NH3+)CO2- redox couple was similarly obtained from the rates with both Fe(III) oxidants, a value of 6x10(6) M(-1) s(-1) for k11 being derived. Both self-exchange rate constants are quite large as is to be expected from the minimal rearrangement that follows conversion of a thiolate to a thiyl radical, and the somewhat lower self-exchange rate constant for the dianionic form of cysteine is ascribed to electrostatic repulsion.     

铁氰化钾化学发光体系测定芦丁

基于在ＮａＯＨ碱性介质中,Ｆｅ（ＣＮ）３－６可以直接氧化芦丁产生强的化学发光这一现象,并结合流动注射分析技术,提出了一种直接化学发光测定芦丁的新方法。该方法测定芦丁的线性范围为１×１０－４～　１×１０－６　ｇ／ｍＬ,检出限为３．４×１０－７　ｇ／ｍＬ（３σ）。对５×１０－６　ｇ／ｍＬ芦丁溶液连续１１次测量的相对标准偏差为３．７％。该方法已成功地用于药片中芦丁含量的测定。     

Energy level alignment at interfaces between 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butyl phenyl)-1, 2, 4-triazole (TAZ) and metals (Ca,Mg, Ag,and Au): experiment and theory

We have performed ultraviolet photoelectron spectroscopy measurements and density functional theory calculations to study the electronic structure at the interface between organic semiconductor (3-(4-biphenylyl)-4-phenyl-5-(4-tert-butyl phenyl)-1,2,4-triazole (TAZ)) and metals (Ca, Mg, Ag, and Au). The basic mechanism of interface states at organic–metal interfaces can be understood by controlling the injection of charge carriers at these interfaces. The position of highest occupied molecular orbital relative to the Fermi level and the magnitude of the interface dipole are measured for each organic–metal interface. For TAZ on Ca, Mg, and Ag, interface states are observed near the Fermi level. However, no interface state is observed for TAZ on Au. It is analyzed qualitatively that the interface state is formed due to interaction of TAZ lowest unoccupied molecular orbital composed of C2p and metal s levels. It is suggested that the interface state plays an important role in charge transport at the interface. The mechanism of formation of interface states and electrical properties are discussed.     

A Selective Colorimetric and Fluorescent Chemodosimeter for Fe(III) Ion Based on Hydrolysis of Schiff Base

An efficient colorimetric and fluorescent chemodosimeter for Fe³⁺ ions has been developed. The visual and fluorescent behaviors of the receptor toward various metal ions were investigated. The receptor shows exclusive response toward Fe³⁺ ions and also distinguishes Fe³⁺ from other cations by color change and unusual fluorescence enhancement in aqueous solution (DMSO/H₂O = 4/1, v/v). Thus, the receptor can be used as a colorimetric and fluorescent sensor for the determination of Fe³⁺ ion. The visual color detection limit and the fluorescence detection limit of the receptor towards Fe³⁺ are (1.42 ± 0.01) × 10^‐6 M and (7.57 ± 0.04) × 10^‐8 M, respectively. The fluorescence microscopy experiments showed that the receptor is efficient for detection of Fe³⁺ in vitro, developing a good image of the biological organelles. The sensing mechanism is proven to be a hydrolysis process     

An Ab initio study of the ligand field and charge-transfer transitions of Cr(CN)(6)(3-) and Mo(CN)(6)(3-)

High-level ab initio calculations on the excited states of Cr(CN)63- and Mo(CN)63- are reported. For the latter complex, a rather large 10 Dq value of 42 000 cm-1 is obtained, reflecting the increased covalency. The lowest lying charge-transfer transitions for both complexes are predicted to be of the type ligand-to-metal, an assignment in agreement with the photochemical behavior of Cr(CN)63-. A good correspondence between the well-known experimental spectrum of the chromium complex and the theoretical CASPT2 excitation energies is found.     

Acetylene decomposition on Rh(100): theory and experiment.

The decomposition of acetylene on a Rh(100) single crystal was studied by a combination of experimental techniques [static secondary ion mass spectrometry (SSIMS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED)] to gain insight into the reaction pathway and the nature of the reaction intermediates. The experimental techniques were combined with a computational approach using density functional theory (DFT). Acetylene adsorbs irreversibly on the Rh(100) surface and eventually decomposes to atomic carbon and gas-phase hydrogen. The combination of experimental and computational results enabled us to determine the most likely reaction pathway for the decomposition process.     

Te(CN)4] versus [Te(CN)3(micro-CN)](n)

Solvent molecules have a great influence on the structure and stability of tellurium tetracyanide; whereas Te(CN)4 x (diglyme)(2) contains monomeric Te(CN)4 units, [Te(CN)3(micro-CN) x diglyme](n) is a coordination polymer.