Synthesis of binuclear complexes of PdCl2 with chiral α,α'-diamino-meta-xylene dioximes H2L1, H2L2, and H2L3, the derivatives of the terpenes (+)-3-carene, (R)-(+)-limonene, and (S)-(-)-α-pinene. Crystal structure of [Pd2(H2L1)Cl4]

Chiral alpha,alpha'-diamino-meta-xylene dioximes H2L1, H2L2, and H2L3 were obtained from the naturally occurring terpenoids (+)-3-carene, (R)-(+)-limonene, and (S)-(-)-alpha-pinene, respectively. Reactions of these ligands with PdCl2 gave the diamagnetic complexes Pd-2(H2L1)Cl-4 (I), Pd-2(H2L2)Cl-4 (II), and Pd-2(H2L3)Cl-4 (III). According to X-ray diffraction data, the crystal structure of complex I consists of acentric binuclear molecules [Pd-2(H2L1)Cl-4]. The coordination polyhedron PdN2Cl2 is a square distorted in a tetrahedral manner (trapezium) made up of two N atoms of the tetradentate bridging cyclic ligand H2L1 and two Cl atoms. The fragments PdCl2 in the complex are cis to each other. According to the H-1 NMR spectra of complexes I-III in CDCl3, the organic ligands are coordinated through the N atoms; in solution, the complexes exist in several forms.