Dimeric Osmium Phthalocyanine Organized in Discrete Columnarly Stacked Assemblies: Structure, Magnetism, and Electrical Conductivity Properties

A Theoretical Probe for Structures, Metal–Metal Bonding, and Electronic Spectra of Paramagnetic Tetrapyrrolic RuII Complex

Dimeric complexes (RuIIPz)2 have been investigated using density functional theory (DFT), where Pz is a porphyrazine ligand that features a 16-atom, 18-π-electron cyclic polyene aromatic skeleton. Structural optimizations in various configurations and spin states indicate that (RuPz)2 favours a Pz–Pz staggered conformer over an eclipsed one; the paramagnetic triplet state with the staggered configuration is found as the global ground state. This agrees with experimental magnetic results of (RuOEPor)2 (OEPor = octaethylporphyrin) and (RuPc)2 (Pc = phthalocyanine). The Ru–Ru bond length was optimized to be 2.38 Å, close to the experimental bond length of 2.40–2.41 Å. The Ru2 doubly bonded nature has been evidenced by the Ru–Ru stretching vibrational frequency of 202 cm–1, bond energy of 30.7 kcal mol–1, and electronic arrangement of σ2π4(nonbonding-δ)4(π*)2. Further confirmation was obtained from high-level wave function theory calculations (complete active space self-consistent field and n-electron valence state second-order perturbation theory). Associated with the solvation of the explicit pyridine accounting for the first coordination sphere and the implicit continuum model for the long-range interaction, the electronic spectra of tetrapyrrolic ruthenium complex were calculated at the time-dependent DFT level.

New classes of porphyrazine macrocycles with annulated heterocyclic rings

The present contribution summarizes the most recent results on the synthesis and chemical physical characterization of the new classes of porphyrazine macrocycles having annulated five- and seven-membered heterocyclic rings, i.e. tetrakis(thiadizole)porphyrazine, TTDPzH 2, tetrakis(selenodiazole)porphyrazine, TSeDPzH 2, tetrakis-2,3-(5,7dipheny-6H-1,4-diazepino)porphyrazine, Ph 8 DzPzH 2, and a number of their metal derivatives, prepared by using, respectively, 3,4-dicyano-1,2,5-thiadiazole, 3,4-dicyano-1,2,5-selenodiazole, and 5,7-diphenyl-2,3-dicyano-6H-1,4-diazepine as monomeric precursors. The available information indicates that, owing to the presence of electron rich and soft atoms ( S , Se ) inserted in the proximity of the porphyrazine core, the TTDPz and TSeDPz macrocycles, closely resembling their phthalocyanine analogues in terms of structural and electronic features and physical behaviour (solubility, thermal stability, vaporizability, etc.), might be promising new materials for applicative properties. Particularly interesting is the operated peripheral ring opening of the TSeDPz macroxycle leading to the formation of octaaminoporphyrazine, followed by its conversion to a tetrakis(pyrazino)porphyrazine. The macrocycles containing the Ph 8 DzPz skeleton, due to the presence of the external non planar diphenyldiazepine units, appear to exhibit a distinct physical behaviour, which can be probably modulated by appropriate alternative substitutions in the 5, 6, and 7 positions of the diazepine rings.

Diphthalocyanine metal complexes and their analogues

The present overview deals with ditetrapyrrolic macrocycles, mainly diphthalocyanine systems, of the following three classes: (a) sandwich-type molecules (I); (b) metal-metal bonded systems (II); (c) single-atom bridged dimers (III). The available information focuses on the structural and electronic features, redox properties and partial oxidation. Practical applications, e.g. electrochromic devices, molecular metals, liquid crystals, non-linear optics, etc., make these classes of complexes particularly attractive and promising materials. The bonding mechanism and the structural, magnetic, conductive and optical properties of these systems are elucidated by density functional calculations.

Tetrakis(thiadiazole)porphyrazines. 4. Direct Template Synthesis, Structure, General Physicochemical Behavior, and Redox Properties of AlIII, GaIII, and InIII Complexes

Monometallic derivatives of tetrakis(1,2,5-thiadiazole)porphyrazine, [TTDPzH2], with main group tervalent metal ions having the formulae [TTDPzMX] (TTDPz = tetrakis(1,2,5-thiadiazole)porphyrazinato dianion; M = Al(III), X = Cl-, Br-, OH-; M = Ga(III), X = Cl-, OH-; M = In(III), X = AcO-) were prepared and investigated by single-crystal X-ray analysis and IR and UV-vis spectroscopy as well as cyclic voltammetry and spectroelectrochemistry. The complexes [TTDPzMX] (M = Al(III), X = Cl-, Br-; M = Ga(III), X = Cl-) were obtained by direct autocyclotetramerization of the precursor 3,4-dicyano-1,2,5-thiadiazole in hot quinoline in the presence of MX3 salts (M = Al(III), Ga(III); X = Cl-, Br-) and were hydrolized to form the corresponding hydroxide derivatives, [TTDPzMOH]. The In(III) complex, [TTDPzIn(OAc)], was obtained from the free-base macrocycle [TTDPzH2] with In(OH)(OAc)2 in CH3COOH. A single-crystal X-ray study was made at 173 K on the two isostructural species [TTDPzMCl] (M = Al(III), Ga(III)), which have space group P, with a = 12.470(14), b = 12.464(13), and c = 13.947(12) angstroms, alpha = 70.72(3), beta = 79.76(3), and gamma = 90.06(3) degrees, V = 2009.3(3) angstroms3, and Z = 4 for [TTDPzAlCl] and a = 12.429(3), b = 12.430(3), and c = 13.851(3) angstroms, alpha = 70.663(6), beta = 79.788(8), and gamma = 89.991(9) degrees, V = 1983.3(7) angstroms3, and Z = 4 for [TTDPzGaCl]. Square pyramidal coordination exists about the M(III) centers, with Cl- occupying the apical position (Al-Cl = 2.171(5) and Ga-Cl = 2.193(1) angstroms). Al(III) and Ga(III) are located at distances of 0.416(6) and 0.444(2) angstroms from the center of the N4 system. The molecular packing consists of stacked double layers with internal and external average interlayer distances of 3.2 and 3.3 angstroms, respectively. IR spectra show nu(Al-Cl) at 345 cm(-1) for [TTDPzAlCl], nu(Al-Br) at 330 cm(-1) for [TTDPzAlBr], and nu(Ga-Cl) at 382 cm(-1) for [TTDPzGaCl]. The UV-vis spectra in weakly basic (pyridine, DMF, DMSO) and acidic solvents (CF3COOH, H2SO4) show the typical intense pi --> pi transition bands in the Soret (300-400 nm) and Q-band regions (640-660 nm), the bands evidencing some dependence on the nature of the solvent, particularly in acidic solutions. Cyclic voltammetry, differential pulse voltammetry, and thin-layer spectroelectrochemical measurements in pyridine and dimethylformamide of the species [TTDPzMX] indicate reversible first and second one-electron reductions, whereas additional ill-defined reductions are observed at more negative potentials. The examined species are much easier to reduce than their phthalocyanine or porphyrin analogues as a result of the remarkable electron-attracting properties of the TTDPz macrocycle which contains annulated strongly electron-deficient thiadiazole rings.

The reduction of oxygen and hydrogen peroxide on dinuclear ruthenium phthalocyanine electrocatalytic surfaces

The electrochemical properties of both mononuclear L2RuIIPc and dinuclear [(THF)Rupc]2 species are described. The former is dominated by ring oxidation and reduction processes while the latter displays a series of metal localized processes. A Pourbaix diagram describes the various surfaces which can be generated by exposing a graphite electrode modified with [(THF)Rupc]2 to aqueous buffer at different polarization over a wide range of pH. The behavior of these various surfaces towards the electrocatalytic reduction of both oxygen and hydrogen peroxide is described. Most importantly, three different regimes of hydrogen peroxide reduction are observed dependent on the nature of the modified electrode surface. At high pH the four electron reduction of oxygen to water is observed via a 2 + 2 mechanism.Key words: phthalocyanine, ruthenium, ruthenium phthalocyanine, cyclic voltammetry, suface modified electrode, Pourbaix diagram, electrocatalysis, oxygen reduction, hydrogen peroxide reduction.