Determination of the dimerization constants of water soluble metallophthalocyanines by calorimetric titration using electron-donating ligands

Self-association of sulfo derivatives of cobalt phthalocyanine in aqueous solution

“…The latter absorbs at λ 615-630 nm against λ 670-675 nm for the monomeric species. The molar absorption coefficient of the dimer at λ 630 is 15 200±50 L mol -1 cm -1 , which is consistent with published data [13,[20][21][22]. No relaxation effects (which are commonly related to change of the aggregate state of the macrocycle) were observed in the electronic absorption spectra [16,20]; this provides an additional proof for the prevalence of dimeric species in solution.…”

“…Presumably, the second linear part of the titration curve reflects only the formation of molecular complex. In keeping with the equilibrium constants, the stability of the pyridine complexes decreases in the series III (K = 2500 L/mol) > II (1600 L/mol) > I (17 L/mol [13,20]). These data may be interpreted in favor of π-π dimers of I-III.…”

“…The dissociation constants K dim decrease in the series III > II > I (K diss = 2.2 × 10 -4 , 1.54 × 10 -4 , and 1.08 × 10 -4 M [13,21], respectively), which characterizes the effect of peripheral substitution on the aggregation of sulfo derivatives of cobalt phthalocyanines in aqueous solution.…”

“…However, association of phthalocyanine metal complexes in solution creates some problems in their use as catalysts [10][11][12]. It is known that metal phthalocyanines in solution form dimers and other associates [13,14]. Dimerization considerably reduces their catalytic activity [15,16] since the formation of some dimeric structures, e.g., π-π dimers, leads to shielding of the reaction center, which hampers interaction with a substrate.…”

The Surface Modification of the Polypropylene by Aqueous Soluble CoII Phthalocyanine to Obtain Materials for Catalysis

“…[2,[6][7][8][9][10][11] However, there is a significant drawback of using these compounds -propensity to self-association in solution. [12][13][14] Processes of self-association of metal phthalocyanines in aqueous and nonaqueous media affect their catalytic properties ambiguously. According to coordination mechanism of catalytic oxidation of RSH, shown in works, [2,[15][16][17][18] association of phthalocyanine catalyst reduces its activity significantly due to the limitations on access to the central metal cation of the oxygen molecules and the substrate.…”