Interactions between phenothiazine drugs and metal ions. Part 1. Palladium(II) and platinum(II) complexes. Crystal and molecular structure of protonated trichloro[10-(2′-dimethylaminopropyl)phenothiazine-S]palladium(II)

Abstract

Phenothiazine drugs form complexes with Pd^II and Pt^II of unusual stoicheiometry, i.e.[MLX₃](L = protonated drug; X = Cl or Br; M = Pd or Pt). The structure of the promethazine complex with Pd^II has been elucidated by single-crystal X-ray crystallography. Crystals are monoclinic, space group P2₁, Z= 2, in a unit cell with lattice parameters a= 11.381(5), b= 9.791(4), c= 9.098(4)Å, β= 100.85(5)°. The structure has been solved using heavy-atom methods and refined by least squares to R 0.036 (R′ 0.039) for 1 524 independent reflections collected by counter methods. The drug is sulphur-bonded to a PdCl_3^– unit, the counter ion being a protonated nitrogen on the drug substituent. The side chain adopts an unusual conformation bending back over the heterocycle in order to facilitate intramolecular hydrogen bonding between the protonated nitrogen and one of the chlorine atoms on the palladium. Proton n.m.r. and solution i.r. data support the existence of this hydrogen bonding in solution. Electronic spectral data both from this work and the literature show that the interaction observed for the above complex is seen for all phenothiazine drugs so far examined. Far-i.r. data confirm the similarity of the equivalent platinum(II) compounds.