Intramolecular stacking of two aromatic rings in the platinum(II) coordination sphere: Preparation, crystal structures, and 1H NMR spectra of bipyridine(N-arylmethyl-1,2-ethanediamine)platinum(II) nitrate

Article abstract of DOI:10.1246/bcsj.73.97

Square-planar complexes with the formula [Pt(L₁)(L₂)](NO₃)₂·nH₂O, where L₁ is bipyridine (bpy) and L₂ is N-benzyl-1,2-ethanediamine (Been) (1) (n = 0), N-(1-naphthyl)methyl-1,2-ethanediamine (Npen) (2) (n = 2), and N-(9-anthryl)methyl-1,2-ethanediamine (Aten) (3) (n = 2), were prepared and X-ray crystal-structure determinations were carried out. The molecular structures of the complex cations revealed that the N-arylmethyl groups are forced to take pseudo axial dispositions due to an intramolecular repulsion from hydrogen atoms of bpy. The aromatic-aromatic interaction between the aromatic rings of ethanediamine derivatives and coordinated bpy caused 2 and 3 to take a conformation where the aromatic ring and bpy stack face-to-face to each other intramolecularly. An intermolecular aromatic-aromatic face-to- face interaction was also observed for 1, 2, and 3 in the crystals. The latter interaction occurs between bpy and the aryl substituent, except for 1. For D₂O solutions of 1 through 3, significant upfield shifts due to the intramolecular stacking were observed in the ¹H NMR spectra for the protons on the half ring of bipyridine, depending on the size of the aromatic ring. The crystal data of 1: monoclinic, P2₁/c, a = 9.884(2), b = 24.717(2), c = 9.560(5) A, β = 113.83(3)°, Z = 4, and R = 0.029. 2: monoclinic, Ia, a = 17.030(5), b = 10.461(4), c = 14.727(4) A, β = 94.72°, Z = 4, and R = 0.023. 3: monoclinic, P(n), a = 10.471(2), b = 8,844(5), c = 15.332(3)A, β = 98.61(2)°, Z = 2, and R = 0.034.