Tetrakis(thiadiazole)porphyrazines. 4. Direct Template Synthesis, Structure, General Physicochemical Behavior, and Redox Properties of A(lIII), Ga(III), and In(III) 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 = AlIII, X = Cl-, Br-, OH-; M = GaIII, X = Cl-, OH-; M = InIII, 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 = AlIII, X = Cl-, Br-; M = GaIII, 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 = AlIII, GaIII; X = Cl-, Br-) and were hydrolized to form the corresponding hydroxide derivatives, [TTDPzMOH]. The InIII 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 = AlIII, GaIII), which have space group P, with a = 12.470(14), b = 12.464(13), and c = 13.947(12) Å, α = 70.72(3), β = 79.76(3), and γ = 90.06(3)°, V = 2009.3(3) Å3, and Z = 4 for [TTDPzAlCl] and a = 12.429(3), b = 12.430(3), and c = 13.851(3) Å, α = 70.663(6), β = 79.788(8), and γ = 89.991(9)°, V = 1983.3(7) Å3, and Z = 4 for [TTDPzGaCl]. Square pyramidal coordination exists about the MIII centers, with Cl- occupying the apical position (Al−Cl = 2.171(5) and Ga−Cl = 2.193(1) Å). AlIII and GaIII are located at distances of 0.416(6) and 0.444(2) Å 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 Å, respectively. IR spectra show ν(Al−Cl) at 345 cm-1 for [TTDPzAlCl], ν(Al−Br) at 330 cm-1 for [TTDPzAlBr], and ν(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 π → π* 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.