Tetrakis(thiadiazole)porphyrazines: 7. Synthesis and structure of μ-oxo-bis[tetrakis(thiadiazole)porphyrazinato-aluminum(III)

Abstract

The complex μ-oxo-bis[tetrakis(thiadiazole)porphyrazinato-aluminum(III)], [( TTDPzAl )2 O ], has been obtained from the corresponding mononuclear Al(III) hydroxo-complex, [ TTDPzAlOH ], by refluxing a solution of this latter in α-chloronaphthalene or by heating the solid hydroxo species (250–300 °C) under vacuum (10-2 mmHg). The complex, which appears as a stable species in air, shows a typical IR absorption at 983 cm-1, assigned as ν as (Al-O-Al) . Contact with water determines disappearance of this absorption consequent to the formation of the related hydroxide. [( TTDPzAl )2 O ], insoluble in most organic non-donor solvents, and very scarcely soluble in dimethylsulfoxide and dimethylformamide, shows some instability in pyridine, with probable breaking of the μ-oxo bridge and formation of the mononuclear hydroxide. Single crystals suitable for X-ray analysis were obtained by subliming [( TTDPzAl )2 O ] under vacuum at 500 °C under a continuous N 2 flow. Crystal data for [( TTDPzAl )2 O ], C 32 Al 2 N 32 OS 8: a = 7.613(2) Å, b = 11.280(2) Å, c = 23.363(5) Å, β = 96.869(3)°, space group P21/c ( n . 14), U = 1991.9(7) Å3, Z = 2, R(F)a = 0.0492, wR(F2) = 0.1024. The μ-oxo bridged complex has a central linear Al-O-Al bond system, with the Al(III) atoms displaced out of the respective N 4 square planar coordination sites by 0.441 Å and the two TTDPz planes lying in an eclipsed position, the overall structure of the complex approaching closely that of the related phthalocyaninato complex [( PcAl )2 O ]. Intermolecular contacts, instead, are definitely different for the two species, the type found present in [( TTDPzAl )2 O ] highly reminiscent of those of other previously reported "thiadiazoleporphyrazine" macrocycles, with the observed short inter-unit contacts between adjacent TTDPz macrocycles again determined by the presence in the TTDPz framework of the annulated peripheral (S, N) -containing heterocycles.