New palladium(II) complexes of the free-base tetrakis[2,3-(5,6-di-2-pyridylpyrazino)porphyrazine], [Py 8TPyzPzH 2], have been prepared and their physicochemical properties examined. The investigated compounds are the pentanuclear species [(PdCl 2) 4Py 8TPyzPzPd], the monopalladated complex [Py 8TPyzPzPd], and its corresponding octaiodide salt [(2-Mepy) 8TPyzPzPd](I) 8. All three Pd (II) complexes have a common central pyrazinoporphyrazine core and differ only at the periphery of the macrocycle, where the simple dipyridinopyrazine fragments present in [Py 8TPyzPzPd] bear four PdCl 2 units coordinated at the pyridine N atoms in the pentanuclear complex, [(PdCl 2) 4Py 8TPyzPzPd], or carry pyridine-N(CH 3) (+) moieties in the iodide of the octacation [(2-Mepy) 8TPyzPzPd] (8+). The structural features of the pentanuclear complex [(PdCl 2) 4Py 8TPyzPzPd], partly supported by X-ray data and solution (1)H NMR spectra of the [(CN) 2Py 2PyzPdCl 2] precursor, were elucidated through one- and two-dimensional (1)H NMR spectra in solution and density functional theory (DFT) calculations. Structural information on the monopalladated complex [Py 8TPyzPzPd] was also obtained from DFT calculations. It was found that in the complex [(PdCl 2) 4Py 8TPyzPzPd] the peripheral PdCl 2 units adopt a py-py coordination mode and the generated N 2PdCl 2 moieties are directed nearly perpendicular to the plane of the pyrazinoporphyrazine ring, strictly recalling the arrangement found for the palladated precursor [(CN) 2Py 2PyzPdCl 2]. NMR and DFT results consistently indicate that of the four structural isomers predictable for [(PdCl 2) 4Py 8TPyzPzPd], one having all four N 2PdCl 2 moieties pointing on the same side of the macrocyclic framework (i.e., isomer 4:0, plus the 3:1 and the 2:2-cis and 2:2-trans isomers), the 4:0 isomer ( C 4 v symmetry) is the predominant form present. According to cyclic voltammetry and spectroelectrochemical results in pyridine, dimethyl sulfoxide (DMSO), and dimethylformamide (DMF), the monopalladated complex [Py 8TPyzPzPd] undergoes four reversible or quasi-reversible one-electron ligand-centered reductions, similar to the behavior also observed for the pentanuclear complex [(PdCl 2) 4Py 8TPyzPzPd], which shows an additional reduction peak attributable to the presence of PdCl 2. Owing to the electron-withdrawing properties of the PdCl 2 units, the pentanuclear complex is easier to reduce than the mononuclear complex [Py 8TPyzPzPd], some related [Py 8TPyzPzM] complexes, and their porphyrin or porphyrazine analogues, so much so that the corresponding monoanion radical is generated at potentials close to 0.0 V vs SCE in DMSO or DMF. In turn, the monoanion of [(2-Mepy) 8TPyzPzPd](I) 8 is also extremely easy to generate electrochemically. Indeed, because of the eight positively charged N-CH 3 (+) groups in this complex the first reduction occurs at potentials close to +0.10 V in DMSO or DMF. The redox behavior of the mono- and pentapalladated complexes has been rationalized on the basis of a detailed DFT analysis of t...

New homo- and heterobimetallic porphyrazine complexes of general formula [(M'Cl(2))LM] (L = tetrakis-2,3-[5,6-di-(2-pyridyl)pyrazino]porphyrazinato dianion), with M = Zn(II), Mg(II)(H(2)O), or Pd(II) in the central cavity and one M'Cl(2) unit (M' = Pd(II), Pt(II)) peripherally coordinated at the pyridine N atoms of one of the dipyridinopyrazine fragments, were prepared and characterized by elemental analyses and IR/UV-visible spectroscopy. Related water-soluble salt-like species, carrying the hexacations [(PtCl(2))(CH(3))(6)LM](6+) (neutralized by I(-) ions), were also prepared and similarly characterized. Retention of clathrated water molecules is a common feature of all the compounds. A detailed (1)H and (13)C NMR investigation in dimethylformamide (DMF-d(7)) and dimethyl sulfoxide (DMSO-d(6)) provided useful information on the type of arrangement in the neutral and hexacationic species of the metalated dipyridinopyrazine fragments, in which the metal centers (Pd(II)/Pt(II)) are bound to the pyridine N atoms ("py-py" coordination) with formation of N(2(pyr))PdCl(2) or N(2(pyr))PtCl(2) coordination sites, the latter one featuring a cis-platin-like functionality. Data obtained in DMF solution of the quantum yield (Φ(Δ)) for the generation of singlet oxygen, (1)O(2), the cytotoxic agent in photodynamic therapy (PDT), indicate that all the neutral and charged complexes, among them particularly those carrying centrally Zn(II) or Pd(II), exhibit excellent photosensitizing properties, this qualifying the externally platinated complexes as potential bimodal PDT/chemotherapeutic anticancer agents. Fluorescence data (Φ(F)) provided additional information on the photoactivity of all the species studied. The following companion paper describes the observed interaction of the Zn(II) hexacation [(PtCl(2))(CH(3))(6)LZn](6+) with a G-quadruplex (G4) structure of the telomeric DNA sequence 5'-d[AGGG(TTAGGG)(3)]-3' in water.

A series of heteropentametallic porphyrazine macrocycles, represented as [(PdCl(2))(4)LM], where L = dianion of tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine and M = Zn(II), Cu(II) Mg(II)(H(2)O) or Cd(II), were prepared by reaction of the corresponding mononuclear [LM] species, and their behavior was examined by UV-visible and NMR spectroscopy, electrochemistry, and thin layer spectroelectrochemistry in nonaqueous media. The PdCl(2) units in [(PdCl(2))(4)LM] are coordinated at the pyridine N atoms of the external dipyridinopyrazine fragments ("py-py" coordination) and are displaced out of the plane of the central pyrazinoporphyrazine macrocycle as verified by (1)H and (13)C NMR data on [(PdCl(2))(4)LZn]. The same arrangement is also strongly suggested by similar NMR data on the Mg(II) and Cd(II) analogues. The predominant component in the synthesized materials among the four predictable macrocyclic isomers has the four exocyclic N(2(py))PdCl(2) square planar coordination sites on the same side of the central macrocyclic framework (4:0 isomer, C(4v) symmetry), and this is accompanied by a minor isomeric component (2:2 cis or trans), in line with previous findings on the pentapalladated species [(PdCl(2))(4)LPd]. IR, UV-visible, and NMR spectral data also provide evidence for transmetalation reactions of the type [(PdCl(2))(4)LMg(H(2)O)] --> [(PdCl(2))(4)LPd] and [(PdCl(2))(4)LCd] --> [(PdCl(2))(4)LPd], with the amount of [(PdCl(2))(4)LPd] formed varying from batch to batch. Dissociation of the four exocyclic PdCl(2) units from [(PdCl(2))(4)LM] occurs in pyridine, but the compounds are stable in N,N-dimethylformamide (DMF) or dimethylsulfoxide (DMSO) and can be stepwise reduced via two one-electron reversible or quasi-reversible processes, prior to an irreversible electroreduction of the bound PdCl(2) group at more negative potentials. This metal-centered reduction leads to a [LM](2-) product which is then further reduced to [LM](3-) and [LM](4-) at the electrode surface. The first two reductions of the heteropentametallic compounds are easier than those of the monometallic [LM] species but generally more difficult than reduction of the related octacationic [L'M](8+) derivatives (L' = the octamethylated free-base dianion) whose redox properties were previously reported. The Cd(II) octacation [L'Cd](8+), isolated as an iodide salt, was also synthesized for the first time in the current study, and its spectroscopic and electrochemical properties are compared to that of the previously examined analogues.