Equilibrium studies on mercury(II)—porphyrins in aqueous solution

Adeyemo, Adegboye; Krishnamurthy, M.

doi:10.1016/s0020-1693(00)82504-9

Cited by 12 publications

(16 citation statements)

References 6 publications

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“…(Thus, the formal value of K 1 is 8.8 AE 0.4 Â 10 À9 M, À log K 1 ¼ 8:06.) The order of magnitude of this value is in accordance with that published in [14] (8.38). The photometric titration could also be carried out in the range of the Q bands.…”

Section: Introductionsupporting

confidence: 92%

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Unique photoreactivity of mercury(II) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

Horváth

Valicsek

Vogler

2004

Inorganic Chemistry Communications

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Section: Introductionsupporting

confidence: 92%

“…In near-neutral solutions, at low concentrations ( 6 2.5 Â 10 À7 M) of H 2 TPPS, Adeyemo and Krishnamurthy [14] found spectral evidence for the formation of 1:1 complex. Although Hg(II) is known to form predominantly Hg(OH) 2 at pH 7 [7], there is no unambiguous information on the ligands in axial positions of the porphyrin complex.…”

Section: Introductionmentioning

confidence: 99%

Unique photoreactivity of mercury(II) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

Horváth

Valicsek

Vogler

2004

Inorganic Chemistry Communications

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“…The apparent stability constant determined for HgP 4is β 1 ′ ) (8.8 ( 0.7) × 10 5 M -1 (lgβ 1 ′ ≈ 5.95), 15 which is in accordance with the only published result lgβ 1 ′ ) 5.62 (converted to pH ) 7 from the reported lgβ 1 ) -8.38). 128 The absorbance of the complex determined in ref 128 was smaller than that for the free-base ligand because the dimerization, that is, the formation of Hg 2 P 2 8was not taken into consideration. In the literature, formation of a complex with such a constitution has not been reported; however, a hint indicating its existence can be seen in the photometric titration curves presented in ref 89 The difficulty of the spectrophotometric study of this species is that the position of its Soret-band (λ ) 422 nm) just slightly differs from that of the HgP 4complex (420.5 nm), thus they can not be distinguished, even by matrix rank analysis.…”

Section: Resultsmentioning

confidence: 93%

Equilibrium, Photophysical, Photochemical, and Quantum Chemical Examination of Anionic Mercury(II) Mono- and Bisporphyrins

2008

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Mercury(II) ion and 5,10,15,20-tetrakis(parasulfonato-phenyl)porphyrin anion can form 1:1, 2:2, and 3:2 (metal ion/porphyrin) out-of-plane (OOP) complexes, from which Hg2P2(8-) has not been identified until now. Identification of this species significantly promoted the confirmation of the composition and the precise elucidation of the equilibrium of Hg3P2(6-). Since the formation of each complex is too fast, their kinetic behavior was studied from the side of dissociation. The rate-determining step in dissociations, as well as in the formation of the 2:2 complex, that is, the dimerization of 1:1 complex, proved to be virtually first-order under these conditions, while the consecutive formations of HgP(4-) and Hg3P2(6-) are second-order reactions. The equilibria can be spectrophotometrically investigated because the Soret- as well as the Q-absorption bands of the free-base ligand are more and more red-shifted in the series of 1:1, 2:2, and 3:2 complexes, and the split of Q-bands disappears as the singlet-1 excited states become degenerate; in the case of bisporphyrins, the bands broaden, especially in the longer-wavelength region of the spectra. The quantum yield and the lifetime of S1-fluorescence from the macrocycle is decreased by the insertion of a mercury(II) ion due to distortion, and in bisporphyrins the luminescence totally ceases because their more complicated structure promotes other ways of energy dissipation. The lifetime of the triplet excited-state is also reduced by metalation. The transient absorption measured upon excitation of Hg3P2(6-) probably originates from Hg2P2(8-) formed by efficient photodissocation during the laser pulse. This photoinduced dissociation is characteristic to out-of-plane complexes, but in metallo-monoporphyrins it needs the energetically higher Soret-excitation; in bisporphyrins, it can take place during irradiation at the longer Q-wavelengths. Investigation of the intramolecular photoredox reactions has proved that for the increased efficiency of the indirect photoinduced LMCT, not the redox potential, but the position of the metal center is responsible. The two orders of magnitude higher photoredux quantum yield for the 3:2 complex, compared to that of the 2:2 species, can be explained by the repulsive effect of the inner mercury(II) ion pushing the other two farther out of the ligand cavity. In bisporphyrins the second excited states are photochemically more reactive than the first ones, while most of the photochemical processes of HgP(4-) originate from the first excited state. According to our quantum chemical calculations, the mercury(II) ion causes the expansion of the porphyrin-cavity; therefore its out-of-plane position is smaller than the value expected based on its ionic radius. In the hitherto unknown 2:2 dimer two 1:1 saucer-shaped monomers are kept together by secondary forces, mostly by pi-pi interaction, but their relative arrangement was not unequivocally determined by the two DFT functionals used. The arrangements with a symmetry axis or plane perpendicul...

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“…2) very much agree with those of the 1 : 1 Hg()-TPPS and Tl()TPPS complexes, 32 and strongly deviate from the Q bands of the Hg 3 P 2 species. 33 This phenomenon suggests that the distortion effect of two Tl ϩ ions is similar to that of one Tl() or Hg().…”

Section: Spectra and Equilibriummentioning

confidence: 97%

Photophysics and photochemistry of water-soluble, sitting-atop bis-thallium(I) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

Valicsek¹,

Horváth²,

Stevenson³

2004

Photochem Photobiol Sci

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In aqueous solutions, thallium(I) ions and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin form a kinetically labile metalloporphyrin of 2 : 1 composition (Tl(2)P(4-)). The formation constant of this sitting-atop (SAT) complex is relatively low (beta2/[H+]2= 3.55 x 10(3) M(-2) at pH = 7), due to the large size and rather small charge of Tl+. As a consequence of the considerably weak metal-ligand interaction in this system, the 1 : 1 species does not appear in detectable concentration. Both the absorption and the emission properties of the Tl(2)P(4-) complex are characteristic for the typical SAT metalloporphyrins. Compared to the corresponding values of the free-base porphyrin, the diminished fluorescence quantum efficiency (Qfl= 0.0131 vs. 0.056) of Tl(2)P(4-) can be accounted for by the heavy-atom effect, while the larger Stokes shift (442 vs. 282 cm(-1)) indicates a stronger distortion of the ligand plane. Both Soret- and Q-band irradiations of the Tl(2)P(4-) complex lead to the degradation of the porphyrin with quantum yields of magnitude 3 x 10(-4). The primary photochemical step in this process is ligand-to-metal charge transfer reaction, which is unusual for normal (coplanar) metalloporphyrins. In the case of SAT complexes, the kinetic lability facilitates the separation of the primary redox products, followed by an irreversible ring-opening of the oxidized porphyrin. Photoinduced electron ejection as a considerable step in the degradation mechanism could be ruled out.

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Equilibrium studies on mercury(II)—porphyrins in aqueous solution

Cited by 12 publications

References 6 publications

Unique photoreactivity of mercury(II) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

Unique photoreactivity of mercury(II) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

Equilibrium, Photophysical, Photochemical, and Quantum Chemical Examination of Anionic Mercury(II) Mono- and Bisporphyrins

Photophysics and photochemistry of water-soluble, sitting-atop bis-thallium(I) 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin

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