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Proprietà redox dei complessi a ponte di ossigeno mu-osso-bis(ftalocianinatoferro(III)) e mu-osso-bis(tetrakis(t-butil)ftalocianinatoferro(III))
No full textNUOVI COMPLESSI DI Pd(II) DI TIPO PORFIRAZINICO MONO- E PENTAMETALLICI COME FOTOSENSIBILIZZATORI IN SOLUZIONE DI DIMETILFORMAMMIDE PER LA PRODUZIONE DI OSSIGENO DI SINGOLETTO, 1O2.
No full textdepositat
Homo/Heteropentanuclear Porphyrazine MgII, ZnII, and PdIIMacrocycles with Externally Pending PdCl2and Pd(CBT)2Units: Synthesis, Physicochemical Characterization, and Photoactivity Studies
No full textRecent work has been developed on two new classes of neutral porphyrazine complexes of formulas [(PdCl2)4Py8PzM]·xH2O (Py8Pz = octakis(2-pyridyl)porphyrazinato anion; M = MgII(H2O), ZnII, PdII) and [{Pd(CBT)2}4Py8PzM]·xH2O (M = MgII(H2O), ZnII CBT = m-carborane-1-thiolate anion). Characterization of all the species has been conducted by IR and UV-visible spectral measurements in a systematic comparison with the corresponding already known mononuclear species [Py8PzM] (M = MgII(H2O), ZnII) and the mono-PdII analogue isolated and presented here for the first time. Comparison includes also the two parent classes of pentanuclear tetrapyrazinoporphyrazines having the more extended π-electron delocalized macrocyclic core Py8TPyzPz. The reported new classes of pentanuclear complexes behave as active photosensitizers in photodynamic therapy (PDT), and due to the high boron content of the CBT derivatives, perspectives for them are open of application in the field of bimodal PDT/BNCT (boron neutron capture therapy) anticancer treatments
One Step Forward to "Stapled" Bis(phthalocyanine) Metal Complexes: Synthesis, Characterization, and Redox Properties of Bis(phthalocyaninato)niobium(IV). X-ray Crystal Structure of the Monoelectronically Oxidized Species [Pc2Nb](I3)(I2)0.5(ClNP)3.5 (ClNP = 1-Chloronaphtalene)
No full textBis(phthalocyaninato)niobium(IV) has been prepared and isolated as a monosolvate, [Pc2Nb]. CINP (CINP = 1-chloronaphthalene). It is a light-brown, stable-to-air Nb(IV) (d(1)) paramagnetic sandwich-like species, which, upon oxidation by It under mild conditions, undergoes a metal-centered monoelectronic oxidation to give the diamagnetic Nb(V) (d(0)) [PC2Nb](+) fragment, with formation of saltlike species of formula [Pc2Nb](I-3)(I-2)0.5(CINP)(3.5) (I). The structure of I has been elucidated by single-crystal X-ray work. Crystals are triclinic: formula C64H32N16Nb . I-3 . 0.5I(2) . 3.5C(10)H(7)Cl, M = 2194.8, a = 17.702(3) Angstrom, b = 18.708(3) Angstrom, c = 13.504(2)Angstrom, V = 4267.5(13) Angstrom(3), alpha = 106.00(2)degrees, beta = 93.39(2)degrees, gamma = 83.26(1)degrees, Z = 2, space group P (1) over bar. The structure of the [Pc2Nb](+) fragment, "stapled" by two inter-ligand C-C sigma bonds (C11A-C11B and C31A-C31B = 1.574(15) Angstrom), together with its color and UV-visible spectral behavior, allows a straightforward assignment of the same "stapled" structure to the unoxidized [Pc2Nb]. The present niobium sandwiched materials reiterate the peculiar structural findings shown only by the previously reported [Pc2Ti]
Tetra-2,3-pyrazinoporphyrazines with Externally Appended Pyridine 2 Rings. 15. Effects of the Pyridyl Substituents and Fused Exocyclic 3 Rings on the UV−Visible Spectroscopic Properties of Mg(II)− 4 Porphyrazines: A Combined Experimental and DFT/TDDFT Study
No full textTwo new MgII porphyrazine macrocycles, the octakis(2-pyridyl)porphyrazinato-magnesium(II), [Py8PzMg- (H2O)], and the tetrakis-[6,7-di(2-pyridyl)quinoxalino]porphyrazinato-magnesium(II), [Py8QxPzMg(H2O)], were prepared by Mg-template macrocyclization processes, and their general physicochemical properties were examined. The previously reported porphyrazine analog, the tetrakis-2,3-[5,6-di(2-pyridyl)-pyrazino]porphyrazinato-magnesium(II), [Py8PyzPzMg(H2O)], has been also considered in the present work. The UV−visible solution spectra in nonaqueous solvents of this triad of externally octapyridinated MgII complexes exhibit the usual profile observed for phthalocyanine and porphyrazine macrocycles, with intense absorptions in the Soret (300−450 nm) and Q-band (600−800 nm) regions. It is observed that the Q-band maximum sensibly shifts toward the red with peak values at 635 → 658 → 759 nm along the series [Py8PzMg(H2O)], [Py8PyzPzMg(H2O)], and [Py8QxPzMg(H2O)], as the extension of the macrocycle π-system increases. TDDFT calculations of the electronic absorption spectra were performed for the related water-free model compounds [Py8PzMg], [Py8PyzPzMg], and [Py8QxPzMg] to provide an interpretation of the UV−visible spectral changes occurring upon introduction of the pyrazine and quinoxaline rings at the periphery of the Pz macrocycle. To discriminate the electronic effects of the fused exocyclic rings from those of the appended 2- pyridyl rings, the UV−visible spectra of [PzMg] and [PyzPzMg] were also theoretically investigated. The theoretical results prove to agree very well with the experimental data, providing an accurate description of the UV−visible spectra. The observed spectral changes are interpreted on the basis of the electronic structure changes occurring along the series
Boron containing mono- and bis-carboranethiolate derivatives of respective formula [(bipy)MCl(CBT)] and [(bipy)M(CBT)2] (M = PdII, PtII)
No full textSynthetic procedures are reported of the new “low molecular weight” mononuclear Pd II and Pt II derivatives of formula [(bipy)MCl(CBT)]⋅0.5CH 3 CN (M = Pd II , Pt II ) and [(bipy)Pt(CBT) 2 ] (CBT = m-carboranethiolate anion) evaluated of interest as potential anticancer agents in boron neutron capture therapy (BNCT). The structure of all
three species has been elucidated by single-crystal X-ray work and further examined by IR and UV–visible spectral behavior. The detailed presentation of the spectral response for all of them in solution of low-donor non-aqueous solvents (CH 3 CN, DMF, DMSO) evidences the presence of a broad absorption in the region 400–500 nm,
already previously observed for the species cis-[(bipy)Pd(CBT) 2 ], this absorption interpreted as due to the presence of one or two metal-CBT environments in the related cis-structurally arranged mono- and bis-CBT
derivatives
Tetra-2,3-pyrazinoporphyrazines with Externally Appended Pyridine Rings. 1. Tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine: A New Macrocycle with Remarkable Electron-Deficient Properties
No full textA new pyrazinoporphyrazine macrocycle carrying externally appended pyridine rings, tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine (hydrated), [Py8TPyzPzH2]·2H2O, was prepared in high yield by direct cyclotetramerization of the precursor, 2,3-dicyano-5,6-di(2-pyridyl)-1,4-pyrazine, [(CN)2Py2Pyz], in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The single-crystal X-ray structure of [(CN)2Py2Pyz] shows a noncoplanar positioning of the pyrazine and pyridine rings in the two slightly different independent molecular units present in the crystal. UV−vis spectra of [Py8TPyzPzH2] were measured in two nondonor solvents (CHCl3, CH2Cl2), a slightly basic solvent (pyridine), and an acidic solvent (CH3COOH). In all cases, the spectral changes are consistent with the occurrence of molecular aggregation and colloidal dispersions which break up with time to give clear solutions containing exclusively the monomeric form of the macrocycle, either neutral [Py8TPyzPzH2] (in CHCl3, CH2Cl2, and CH3COOH) or dianionic [Py8TPyzPz]2- (in pyridine). A spectrally monitored titration of [Py8TPyzPzH2] in CH2Cl2 with TBA(OH) shows the loss of two protons from the macrocyclic core and quantitative conversion of [Py8TPyzPzH2] to [Py8TPyzPz]2-. Cyclic voltammetry and thin-layer spectroelectrochemical measurements show that [Py8TPyzPzH2] is present in CH2Cl2 while [Py8TPyzPz]2- is present in pyridine, but both forms of the compound exhibit identical electrochemical behavior, consistent with a conversion of the dianion to the neutral porphyrazine in pyridine prior to electroreduction via four reversible one-electron transfer steps. No oxidations of the macrocycle are observed in either solvent containing 0.1 M tetrabuthylammonium perchlorate (TBAP). A comparison of the electrochemical behavior for [Py8TPyzPzH2] with what is reported for related phthalocyanine and porphyrazine analogues highlights the remarkable electron-accepting properties of the presently investigated free-base macrocycle
Tetrakis(thiadiazole)porphyrazines. 6. Spectroelectrochemical and Density Functional Theory Studies of the Anions [TTDPzM]n- (n = 1-4; M = ZnII, MgII(H2O), CuII, 2HI )
No full textFollowing previous cyclic voltammetric studies of tetrakis(thiadiazole)porphyrazines [TTDPzM] where M = ZnII, MgII(H2O), CuII, or 2HI in nonaqueous media, a thin-layer spectroelectrochemical investigation was carried out in pyridine to characterize each stepwise one-electron reduction of the electrogenerated [TTDPzM]n− complexes where n = 1−4. A similar UV−visible spectrum was observed for each form of the anion, independent of the central metal ion and detailed theoretical calculations by density functional theory (DFT) and time-dependent DFT (TDDFT) methods were applied to interpret the spectral features of [TTDPzZn]n− (n = 1−4) which was selected as representative for describing the ground and excited-state electronic structures of the entire [TTDPzM]n− series. The use of two exchange-correlation functionals, the pure, asymptotically correct statistical average of orbital potentials (SAOP) and the hybrid B3LYP functionals, proved to be essential for attaining a correct assignment of the key spectral features. The nature and intensity of the main spectral features are highlighted and interpreted on the basis of the ground-state electronic structure of the complexes
Tetrakis(thiadiazole)porphyrazines. 5. Electrochemical and DFT/TDDFT Studies of the Free-Base Macrocycle and Its Mg(II), Zn(II), and Cu(II) Complexes
No full textThe redox properties of the phthalocyanine-like tetrakis(thiadiazole)porphyrazines, [TTDPzM] (M = MgII(H2O), ZnII, CuII, 2HI), were investigated by cyclic voltammetry, and their ground- and excited-state electronic properties were studied in detail by density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Bulk and specific (axial ligation) solvent effects on the molecular and electronic structure were also taken into account. The title compounds show stepwise reversible ligand-centered one-electron reductions in the range 0 to −2.0 V vs SCE, with E1/2 values being systematically less negative than corresponding reduction potentials for the same processes of the phthalocyanine (Pc) analogues. No electroxidations were observed at positive potentials. The observed redox behavior is rationalized on the basis of the ground-state electronic structures which reveal that replacement of the benzo rings of the Pc macrocycle by electron-withdrawing thiadiazole rings induces a large stabilization of both the HOMO and LUMOs in the investigated macrocycles. An excellent correlation is found between the first one-electron reduction potentials and the gas-phase LUMO energies along the series. The same sequence in the first reduction potentials is theoretically reproduced in pyridine, even if the ZnII and MgII complexes are assumed to be in the axially ligated form, [TTDPzM(py)]. TDDFT calculations of the lowest excited states of the ZnII, MgII, and CuII complexes in pyridine provide an accurate description of their UV−visible spectra. The calculated optical spectra for the free-base macrocycle in chlorobenzene and pyridine confirm previous data in that the thiadiazoleporphyrazine [TTDPzH2] is mostly present in pyridine in its deprotonated form [TTDPz]2-. DFT results, in keeping with electrochemical data, indicate, however, that in pyridine it is the neutral species [TTDPzH2] being reduced instead of its deprotonated form [TTDPz]2-
Tetra-2,3-pyrazinoporphyrazines with peripherally appended pyridine rings. 20. Mono- and pentanuclear AlIII and GaIII complexes: synthesis and physicochemical and photoactivity studies
No full textThe autocyclotetramerization of the precursor 2,3-dicyano-5,6-di(2′-pyridyl)pyrazine [(CN)2Py2Pyz] in the presence of MCl3 compounds (M = AlIII, GaIII) leads to the formation of the new mononuclear porphyrazine complexes [Py8TPyzPzMCl]·xH2O (Py8TPyzPz = tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato anion). From these species, the hydroxide analogues [Py8TPyzPzMOH]·xH2O were obtained by contact with hot water, and their corresponding pentanuclear species [(PdCl2)4Py8TPyzPzMCl]·xH2O could be easily formed by the reaction with PdCl2. Physicochemical characterization of the mono- and pentanuclear macrocycles was based on elemental analysis, and mass, powder X-ray, and IR spectra. UV-vis spectral studies of the mononuclear species in solutions of DMF, DMSO, or pyridine (c ≈ 10-5-10-6 M) indicate (mainly in DMF and DMSO) the initial presence of aggregation, in some cases accompanied by the concomitant occurrence for the complex of a one-electron reduction. While disaggregation into a single species evolves spontaneously over time, the -1 charged species, eventually also found present, can be brought back to its neutral form by addition of a slight amount of HCl, the final spectrum showing the presence of the starting neutral species in its pure monomeric form. Similar aspects were faced also for the parent pentanuclear complexes. Cyclic voltammetry experiments, conducted for the mono-/pentanuclear complexes in DMF and DMSO (c ≈ 10-4 M), exhibit progressive one-electron reductions (1 → 4) characterized by E1/2 values (V vs SCE) positioned to significantly less negative values than those known for the phthalocyanine (Pc) analogues, these data confirming the previously already proven higher electron-deficient character of the MII derivatives of the Py8TPyzPz macrocycle with respect to Pc. The role of the present new series of AlIII and GaIII macrocyclic species to act as photosensitizers for the generation of singlet oxygen, 1O2, the cytotoxic agent in the anticancer treatment known as photodynamic therapy (PDT), has been explored in DMF/HCl. Among the quantum yields φΔ, the value found for the GaIII complex [Py8TPyzPzGaCl] (0.68), practically coincident with that observed for the TTDPz analogue (0.69), is well above those of most porphyrazines analogues (φΔ = 0.4-0.6), a result encouraging further research work for potential applications in the biochemical field
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