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, [TTDPzH(2)), 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, [TTDPzln(OAc)], was obtained from the free-base macrocycle [TTDPzH(2)] with ln(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 (1) over bar, with a = 12.470(14), b = 12.464(13), and c = 13.947(12) angstrom, alpha = 70.72(3), beta = 79.76(3), and gamma = 90.06(3)degrees, V = 2009.3(3) angstrom(3), and Z = 4 for [TTDPzAICI] and a = 12.429(3), b 12.430(3), and c = 13.851(3) angstrom, alpha = 70.663(6), beta = 79.788(8), and gamma = 89.991(9)degrees, V = 1983.3(7) angstrom(3), and Z = 4 for [TTDPzGaCl]. Square pyramidal coordination exists about the Mill centers, with Cl- occupying the apical position (Al-Cl = 2.171(5) and Ga-Cl = 2.193(1) angstrom). Al-III and Ga-III are located at distances of 0.416(6) and 0.444(2) angstrom from the center of the N-4 system. The molecular packing consists of stacked double layers with internal and external average interlayer distances of 3.2 and 3.3 angstrom, respectively. IR spectra show v(Al-Cl) at 345 cm(-1) for [TTDPzAICI], v(Al-Br) at 330 cm(-1) for [TTDPzAlBr], and v(Ga-Cl) at 382 cm(-1) for [TTDPzGaCI]. 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 Sorel (300-400 nm) and Q-band regions (640-660 nm), the bands evidencing soma 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.