Study of Phenothiazine— and Chlorpromazine—Iodine Complexes

Abstract

In the solid state, phenothiazine (PH) complexes with iodine to yield a resistivity minimum of 350 Ω·cm at 2:3 stoichiometry. The chlorpromazine (CPZ):I₂ system behaves likewise, the minimum resistivity is 420 Ω·cm. The ESR signal intensities also peak at this ratio. Conductimetric titrations in acetonitrile solution indicate a stoichiometry between 1:2 and 2:3 for the PH:I₂ complex. CPZ·HCl produces a conductivity peak at 1:2, while freshly prepared free base CPZ complexes with I₂ in a 1:1 ratio at room temperature. CPZ aged in solution or in the solid state yields a 2:3 complex at room temperature changing to 1:2 at 50°C with I₂ in acetonitrile. Infrared spectra of these complexes are reported and discussed. Those of the CPZ:I₂ complex resemble that of liquid or supercooled CPZ rather than that of solid CPZ. The CPZ:I₂ as well as the CPZ·HCl:I₂ complexes show a new band at about 1700 cm⁻¹. Palladous chloride tests of the complexes were negative, indicating the absence of iodide ions. From the similarity of the PH:I₂ and CPZ:I₂ complexes in their electrical properties and in view of the fact that the stable form for both occurs for the 2:3 ratio it is likely that the main donor activity of CPZ resides in the phenothiazine nucleus and not in the side chain. However, there is evidence of at least three different complex species in the PH:I₂ or CPZ:I₂ systems. The I₂ complexes of both PH and CPZ strongly resemble the high‐temperature forms of their donor parents; thus it is not unlikely that self‐complexing takes place in PH and in CPZ, especially at elevated temperature.