Comparison of mol-ecular structures of cis-bis-[8-(di-methyl-phosphan-yl)quinoline]-nickel(II) and -platinum(II) complex cations

Abstract

The crystal structures of the complexes (SP-4-2)-cis-bis-[8-(di-methyl-phosphan-yl)quinoline-κ² N,P]nickel(II) bis-(perchlorate) nitro-methane monosolvate, [Ni(C₁₁H₁₂NP)₂](ClO₄)₂·CH₃NO₂ (1), and (SP-4-2)-cis-bis-[8-(di-methyl-phos-phan-yl)quinoline-κ² N,P]platinum(II) bis-(tetra-fluoro-borate) aceto-nitrile monosolvate, [Pt(C₁₁H₁₂NP)₂](BF₄)₂·C₂H₃N (2), are reported. In both complex cations, two phosphanyl-quinolines act as bidentate P,N-donating chelate ligands and form the mutually cis configuration in the square-planar coordination geometry. The strong trans influence of the di-methyl-phosphanyl donor group is confirmed by the Ni-N bond lengths in 1, 1.970 (2) and 1.982 (2) Å and, the Pt-N bond lengths of 2, 2.123 (4) and 2.132 (4) Å, which are relatively long as compared to those in the analogous 8-(di-phenyl-phosphan-yl)quinoline complexes. Mutually cis-positioned quinoline donor groups would give a severe steric hindrance between their ortho-H atoms. In order to reduce such a steric congestion, the Ni^II complex in 1 shows a tetra-hedral distortion of the coordination geometry, as parameterized by τ₄ = 0.199 (1)°, while the Pt^II complex in 2 exhibits a typical square-planar coordination geometry [τ₄ = 0.014 (1)°] with a large bending deformation of the ideally planar Me₂Pqn chelate planes. In the crystal structure of 2, three F atoms of one of the BF₄ ^- anions are disordered over two sets of positions with refined occupancies of 0.573 (10) and 0.427 (10).

Keywords: 8-quinolylphosphane; asymmetrical bidentate ligand; crystal structure; square-planar coordination; tetra­hedral distortion; trans influence.