Crystal and molecular structures of bis[8-(diphenylphosphino)-quinoline] palladium(II) complexes: Pd(Ph2Pqn)₂XY (XY = Cl₂, Br ₂ or CIBF₄)

The complex chloride, Pd(Ph₂Pqn)₂Cl₂ (Ph₂Pqn = 8-(diphenylphosphino)quinoline), crystallized either in yellow plates (1a: from CH₂Cl₂/Et₂O) or in orange needles (1b: from MeOH/Et₂O). The corresponding bromide, Pd(Ph₂Pqn)₂Br₂, initially deposited as yellow block crystals (2a) from MeOH/Et₂O, turned to orange prisms (2b) on standing in the mother liquor. The X-ray crystallographic analyses of 1a and 2a revealed that two Cl^- and Br^- anions, respectively, were located above and below the square-planar Pd¹¹ coordination plane of cis(P)-[Pd(Ph₂Pqn)₂]²⁺. Although the distances of Pd⋯Cl (3.262(3) and 3.386(3) A) and Pd⋯Br (3.432(2) and 3.505(2) Å) in 1a and 2a, respectively, were too long for a bonding interaction between Pd¹¹ and X^-, weak Pd ¹¹⋯X~ charge-transfer interactions seem to be responsible for the yellow colors of these crystals. In contrast, in 2b, the Pd¹¹ formed an elongated square-pyramidal five-coordinate complex, [Pd(Ph ₂Pqn)₂Br]⁺, with a somewhat long Pd-Br bond (3.0136(8) A) at the apical position. The crystal structure of Pd(Ph ₂Pqn)₂ClBF₄ (4) revealed that the Pd ¹¹ center in 4 took an extremely distorted square-planar coordination geometry with the Pd-Cl bond of 2.375(2) Å, while one of the Ph ₂Pqn ligands coordinated through only P;cis(P)-[PdCl(Ph ₂Pqn-κP,N)(Ph₂Pqn-κP)]BF₄.