The crystal and molecular sturctures of R₂SnCl₂(1,10-phenanthroline), R = iPr, Cy, CH₂Ph and R₂ = Me, Ph: a comparison between solid state and theoretical structures

Abstract

The crystal and molecular structures of four diimine adducts formed between R₂SnCl₂ [R = iPr, Cy. CH₂Ph; and R₂ = Me, Ph] and 1,10-phenanthroline have been determined at room temperature. The colorless crystals of R = iPr are monoclinic, space group P2₁/c with unit cell dimensions a = 8.261(2) A, b = 15.125(3) A, c = 15.804(2) A, β = 104.82(1), Z = 4 and Dx = 1.586 Mg m⁻³. The yellow crystals of R = Cy are monoclinic, space group P21/n with unit cell dimensions a = 10.474(1) A, b = 16.167(2) A, c = 14.341(3) Å, β = 101.46(1)°, Z = 4 and Dx = 1.496 Mg m⁻³. Orange crystals of R = CH₂Ph are monoclinic, space group P2₁/n with unit cell dimensions a = 10.356(3) A, b = 17.540(2) Å, c = 13.817(9) A, β = 105.93(5)°. Z = 4 and Dx = 1.519 Mg m⁻³. The colorless crystals of R₂ = Me, Ph are monoclinic, space group P2₁/n with unit cell dimensions a = 9.118(2) Å, b = 11.023(2) A. c = 18.712(2) A, β = 93.03(1), Z = 4 and Dx = 1.634 Mg m⁻³. The structures were solved by direct methods and each refined by a full-matrix least-squares procedure to final R= 0.045 using 2200 reflections for R = iPr; to R = 0.043 using 2644 reflections for R = Cy; to R = 0.045 using 2576 reflections for R = CH₂Ph; and to final R = 0.036 for 2538 reflections for R₂ = Me, Ph. The solid state structures of R₂SnCl₂(phen) feature distorted octahedral tin atom geometries with a trans disposition of the R substituents. A systematic trend to longer Sn-Cl and Sn-N distances with decreasing Lewis acidity is found, however, with a relatively large spread of values which is often correlated in the case of Sn-Cl with Cl…H interactions. The structures of R₂SnCl₂ (phen) have also been investigated employing ab initio methods at the Hartree-Fock SCF level of theory so that a correlation may be made between the R₂SnCl₂ (phen) structures in the presence and absence of crystal packing effects. The calculated structures are generally more symmetric suggesting that there is no inherent chemical reason for a lack of symmetry in the solid state. Further, generally there is an elongation of Sn-ligand distances in the gas phase structures. These two key observations point to the importance of crystal packing effects on molecular geometry as well on the derived interatomic parameters.