Lewis-Base Adducts of Lead(II) Compounds. XII. Synthetic, Spectroscopic and Structural Studies of Some 1:1 Adducts of Lead(II) (Pseudo-)Halides With Aromatic Bidentate Ligands

Abstract

Syntheses and room-temperature single-crystal X-ray structure determinations are recorded for some 1 : 1 adducts of lead(II) (pseudo-)halides with 1,10-phenanthroline (' phen ') and 2,2'-bipyridine (' bpy '). [( phen )PbX₂](∞|∞), X = Cl , Br, I, have been refined in a common monoclinic C2/c setting, a ≈ 16.2, b ≈ 10.6, c ≈ 8.2₅ Ǻ, β 105°, Z = 4 f.u .; (conventional R on |F| 0.034, 0.046, 0.043 for N_o = 1694, 1626, 1387 independent, 'observed' (I > 3σ(I)) reflections respectively); [( bpy )PbI₂](∞|∞) is isomorphous with similar cell dimensions (R 0.035 for N_o 1263), but, in its chloride counterpart, the symmetry is degraded to P2₁/c, a 15.336(5), b 9.476(5), c 8.191(3) Ǻ, β 92.81(3)°, Z = 4 (R 0.041 for N_o 2849). In the C2/c model the lead atoms are disposed on crystallographic 2 axes, as also are the associated N,N′- bidentate ligands, with the six-coordinate (cis-N₂) Pb (μ-X)₄ environments linked in an infinite …(μ-X)₂Pb(μ-X)₂Pb… one-dimensional polymeric chain by bridging halogen atoms. A somewhat similar, albeit more complex, array is found in [( bpy ) Pb (SCN)₂](∞|∞), monoclinic, C2/c, a 17.655(6), b 12.027(3), c 6.794(1) Ǻ, β 107.03(2)°, Z = 4 (R 0.028 for N_o 1064), isomorphous with its previously studied phen analogue, in which a web of bridging SCN units is found. Stacks of successive strands up b have interleaving arrays of ligands and (pseudo-)halide atoms. The far-infrared spectrum of [( phen )PbCl₂] shows four strong, broad bands at 152, 144, 116 and 96 cm^-1 which are assigned as vPb-Cl. The corresponding bands in the bromo and iodo complexes are shifted to below 100 cm^-1, revealing sharper bands at about 120 and 150 cm^-1 which are assigned to vPb -N modes. The low wavenumbers of the vPb-X bands are indicative of weak Pb-X bonding. The far-infrared spectrum of the previously reported [( phen ) Pb (NCS)₂] complex is similar to that of the chloro complex, consistent with its similarity in structure.