The Detection of a Type of Reaction Intermediate in the Combination of Metal Ions with Porphyrins

Fleischer, Everly B.; Wang, Jui H.

doi:10.1021/ja01499a004

Cited by 113 publications

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“…The cause for this was the presence or absence of single gold adatoms beneath individual tetra-phenylporphyrin (TPP) molecules [30]. The gold adatom forms a coordination bond with the porphyrin core, similar to what has been suggested as a reaction intermediate in the formation of metalloporphyrins in solution [31] and on a Ag(111) surface [32], or of TPP [33] or Br 4 TPP [34] molecules (i.e., the same as in the present work) on a Cu(111) surface. The appearance of our molecules strongly depends on the applied bias voltage: At −0.5 V all molecules appear at a similar height, while at around −1 V two dark and one bright molecular appearances can be found [ Fig.…”

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Observing single-atom diffusion at a molecule-metal interface

et al. 2016

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The dynamics at the interface between a close-packed porphyrin monolayer and Au(111) is investigated by time-dependent scanning tunneling microscopy, detecting the motion of single-interface adatoms in real space. Imaging sequences reveal predominant switching of the molecular appearance in adjacent molecules, pointing to a spatial correlation that is consistent with adatom diffusion from one molecule to the next. In some cases, the number of switching molecules is drastically increased, indicating collective switching events. In addition to the thermally induced motion of adatoms at the interface, also voltage pulses from the microscope tip can induce the process-revealing different yields in agreement with the model of adatom hopping. DOI: 10.1103/PhysRevB.94.035416 The interface between organic molecules and metal substrates plays a key role for many properties that are important, for instance, in catalytically driven reactions [1,2] and for charge transport [3]. The study of such systems gives detailed insight into fundamental processes that take place at an organic-inorganic interface. For an in-depth understanding, it is advantageous to use a scanning tunneling microscope (STM) for imaging because it provides information about the local environment of each individual molecule, which is important since the molecular properties might differ locallydue to defects, step edges, or different areas of a surface reconstruction [4,5]. For instance, individual C 60 molecules were found to change between dark and bright appearances in STM images, caused by the diffusion of surface [6] or bulk [7] vacancies, charge transfer between molecule and surface [8], or adsorption on small metal islands [9].Adatoms are known to diffuse on close-packed metal surfaces if the thermal energy is sufficient for their detachment from step edges [10]. When molecules are adsorbed on such a surface, the adatoms can interact with and even be trapped by molecules [11][12][13][14][15], leading to characteristic metallic nanostructures that reflect the molecular shape [16][17][18]. In addition to these self-organized structures, manipulation of single adatoms has been used to bring them in contact with molecules [19,20]. So far, real space studies of the molecule-surface interaction have been done mainly under static conditions [21,22] or focus on the lateral diffusion of molecules on surfaces [23][24][25]. Here, we report the dynamic behavior at the molecule-metal interface by observing the motion of individual gold adatoms underneath a molecular monolayer on Au(111) in time.As a molecular system we have chosen tetrabromophenylporphyrin [Br 4 TPP; Fig. 1(a) The appearance of our molecules strongly depends on the applied bias voltage: At −0.5 V all molecules appear at a similar height, while at around −1 V two dark and one bright molecular appearances can be found [ Fig. 1(b)]. The two dark molecules could be identified as two tautomers without a gold adatom, while bright molecules have a single gold adatom underneath, causing the shift i...

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Observing single-atom diffusion at a molecule-metal interface

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“…Because the two pyrrolenine groups can potentially bind to the metal ion, the overall metalation reaction will consist of at least two steps, i.e., the coordination step of two pyrrolenine nitrogens to form an intermediate, the so-called sitting-atop (SAT) complex, M(H2por) n+ , 31 in which two protons on the pyrrole nitrogens still remain, [32][33][34][35] and the deprotonation step of the SAT complex to form the metalloporphyrin, as shown by Eqs. (2) and (3), respectively.…”

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confidence: 99%

Dynamic Study of Metal-Ion Incorporation into Porphyrins Based on the Dynamic Characterization of Metal Ions and on Sitting-Atop Complex Formation

2001

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The metalloporphyrin formation reaction is one of the important processes from both analytical and bioinorganic points of view.The large molar absorption coefficient and very high stability of the metalloporphyrins are very useful for the highly sensitive analysis of trace amounts of metal ions, and the size selectivity of the porphyrins is valuable for the separation of various kinds of metal ions. 1-7 A variety of metalloporphyrin formation rates are also applicable for the kinetic analysis of metal ions. We succeeded in the detection of the sitting-atop (SAT) copper(II) complex of TPP (5,10,15,20-tetraphenylporphyrin) in acetonitrile (AN) as a solvent with a very low Brønsted basicity, where two pyrrolenine nitrogens in the Cu(II)-SAT complex coordinate to the metal ion and two protons still remain on the pyrrole nitrogens. The structure parameters around the copper(II) ion in the Cu(II)-SAT complex, as determined by a fluorescent EXAFS method, suggest an axially elongated and equatorially distorted six-coordinate geometry. We measured the rates of the formation reaction of the SAT complexes for a series of transition metal(II) ions in AN using the stopped-flow technique. We propose the mechanism where there is a rapid deformation equilibrium of the porphyrin ring prior to the rate-determining step of the bond rupture of a coordinated solvent molecule on the metal(II) ion. Furthermore, we measured the rates of the deprotonation reaction of the Cu(II)-SAT complex by some Brønsted bases and indicated that the rate-determining step is the attack of the base on the proton of the pyrrole nitrogen in the SAT complex. Finally, a unified mechanism relevant to the porphyrin metalation mechanism has been proposed.

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“…The presence of the isobestic points indicates the absence of other light-absorbing forms of porphyrin, such as sitting-atop (SAT) complexes. [13,26] The formation of СuМР was studied at the constant concentration of H 2 MP and various excesses of Сu(NО 3 ) 2 ×3Н 2 О in systems I-IV. The reaction obeys the linear kinetic Equation (28) and is characterized by the pseudo-first order rate law in H 2 МР.…”

Section: Kinetics Of Complex Formation In Reaction Systems I -Vimentioning

confidence: 99%

“…Obviously, the stability of the complexes of porphyrin dications with halogens will be higher in such solvents. This fact allows us to interpret the data obtained in System (34) by Fleischer [26] in a new way.…”

Section: Fleischer's Sat-complexmentioning

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Effect of pH on Formation of Metalloporphyrins

Sheinin¹,

Симонова²,

Ratkova³

2008

MHC

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Although complexation reactions of porphyrins with metal salts in organic solvents have a long research history, the influence of pH on these processes was not studied. The main reason is complications connected with the pH measurements in nonaqueous solutions. To solve this problem the special instrumentation was created for application of the spectropotentiometric method (spectroscopy + pH-metry with glass electrode) in nonaqueous solutions. Using this method it became possible to investigate complexation reactions at different pH values using electronic absorption spectroscopy. The p H control of reaction systems allows us to explain the peculiarities of metalloporphyrins formation without invoking the Fleischer's idea of SAT-complexes.

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The Detection of a Type of Reaction Intermediate in the Combination of Metal Ions with Porphyrins

Cited by 113 publications

References 0 publications

Observing single-atom diffusion at a molecule-metal interface

Observing single-atom diffusion at a molecule-metal interface

Dynamic Study of Metal-Ion Incorporation into Porphyrins Based on the Dynamic Characterization of Metal Ions and on Sitting-Atop Complex Formation

Effect of pH on Formation of Metalloporphyrins

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