AcidBase Properties and Stability
of (Hydroxo)tetra(carboxy)phthalocyaninatoaluminum(III)

T. N. Sokolova*, T. N. Lomova*, S. V. Zaitseva*, S. A. Zdanovich*,
E. E. Suslova*, and V. E. Maizlish**

* Institute of Chemistry of Nonaqueous Solutions, Russian Academy of Sciences,
Akademicheskaya 1, Ivanovo, 153045 Russia

** Ivanovo State University of Chemical Technology,
pr. Engel’sa 7, Ivanovo, 153460 Russia

Received January 22, 2004

Abstract—The reactions of the (OH)AlPc(3-COOH)₄ and (OH)AlPc(4-COOH)₄ complexes with concentrated
H₂SO₄ are studied. Monoprotonated, diprotonated, and triprotonated forms of (OH)AlPc(3-COOH)₄ and two
protonated forms of (OH)AlPc(4-COOH)₄ (a monocation and a dication) are identified in the gas phase and sul-
furic acid solutions by electron absorption spectroscopy and MP3 calculations. This is evidence that the com-
plexes are weak bases. Each of the protonated species exists as isomers differing in the location of protons,
which can be attached to meso-nitrogen or to carbonyl oxygen atoms. The protonation of the (OH)AlPc(3-
COOH)₄ complex yields O···H⁺···N bridges, which show themselves in a special way in electronic absorption
spectra. The decomposition kinetics of the complexes are comprehensively studied, and a multistep decompo-
sition mechanism is substantiated. Kinetically significant are the reversible extra protonation of the original pro-
tonated complex and the irreversible dissociation of the Al–N coordination bonds. The latter is the rate-limiting
step and results in two covalent N–H bonds. Furthermore, the reaction involves the irreversible protonation of
the original complexes and the decomposition of the resulting phthalocyanine.

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