The spectroscopic and chemical behavior of the six-coordinate adducts formed by the association of chloro-meso-te-traphenylporphinatochromium(III), Cr(TPP)(Cl), and neutral oxygen, sulfur, and nitrogen donor ligands in nonaqueous solutions is described. In nonaqueous media, in the presence of a neutral ligand, Cr(TPP)(Cl) forms six-coordinate adducts of the type Cr(TPP)(Cl)(L) and Cr(TPP)(Cl)(B), where L and B denote neutral N-donor and O- or S-donor ligands, respectively. This behavior is confirmed by visible spectroscopy, spectrophotometric titrations, and conductivity data. Equilibrium constants for the substitution reaction Cr(TPP)(Cl)(B) + L ⇌ Cr(TPP)(Cl)(L) + B are reported. The N-donor ligands are found to bind much more strongly to the Cr(III) center than the O- or S-donors. The replacement of acetone by 1-methylimidazole in the complex Cr(TPP)(Cl)(acetone) in 60% acetone/toluene (v/v) at 25 °C occurs with an equilibrium constant of 4.0 × 10 6 . Fitting the EPR spectra of the six-coordinate adducts obtained from frozen solutions at 78 K to the spin Hamiltonian H=β e [g x H x S x + g y H y S y + g z H z S z ] + D[S z 2 —%5/4] + E[S x 2 —S y 2 ], and using an assumed isotropic value for g of 1.995, results in values for |D| in the range 0.156 ± 0.012 cm -1 for complexes of the type Cr(TPP)(Cl)(L) and values in the range 0.232 ± 0.004 cm -1 for the complexes of the type Cr(TPP)(Cl)(B). The only observed exception was the CH3CN adduct for which a value of 0.208 cm -1 was obtained. In all cases |E| was found to be small, having a maximum value of 0.013 cm -1 for the complex Cr(TPP)(Cl)(acetone). The Cr(octaethylporphyrin) complexes behave similarly.
ASJC Scopus subject areas
- Colloid and Surface Chemistry