Structural Chemistry of Poly(ethylene glycol) Complexes of Lead(II) Nitrate and Lead(II) Bromide

The reaction of 1:1 stoichiometries (1:1.5 for the nitrate/tetraethylene glycol (EO4) and pentaethylene glycol (EO5) complexes) of PbX2 (X = NO3, Br) with five- to eight-donor poly(ethylene glycols) (PEGs) in 3:1 CH3CN/CH3OH (CH3CN only for the nitrate/EO5 complex) followed by solvent evaporation resulted in six crystalline materials upon which X-ray structural analyses were carried out: [Pb(NO3)2(EO4)] n , [Pb(NO3)2(EO5)], [Pb(NO3)2(EO6)], [PbBr(EO5)(μ-Br)PbBr2]·H2O, [PbBr(NCMe)(EO6)]2[PbBr2(EO6)][PbBr3]2, and [PbBr(EO7)][PbBr3]. The nitrates crystallize as tight ion pairs with the PEG ligands coordinating in an equatorial plane around the Pb2+ ions. Because EO4 has only five oxygen donors, this complex exhibits steric unsaturation which is overcome by a monodentate interaction with a third nitrate anion that is also coordinated to a neighboring Pb2+ ion. The six donors of EO5 coordinate in an equatorial plane resulting in a 10-coordinate complex with trans, twisted, bidentate nitrate anions. The seven-donor hexaethylene glycol (EO6) only uses six of its oxygen donors to coordinate Pb2+. [Pb(NO3)2(EO4)] n is monoclinic, P21/c, with a = 7.902(3) Å, b = 22.136(6) Å, c = 8.910(2) Å, β = 90.96(3)°, and Z = 4. [Pb(NO3)2(EO5)] is triclinic P1̄, with a = 9.332(3) Å, b = 10.025(3) Å, c = 11.688(4) Å, α = 68.41(3)°, β = 68.39(3)°, γ = 68.58(3)°, and Z = 2. [Pb(NO3)2(EO6)] is monoclinic P21/c, with a = 16.289(4) Å, b = 10.773(4) Å, c = 12.329(4) Å, β = 106.77(2)°, and Z = 4. Lead(II) bromide complexes with PEGs tend to crystallize as PEG complexed cations with polymeric lead(II) bromide anions. In the EO5 complex, bromide anions in the polymer also coordinate to the PEG-wrapped Pb2+ cations. The hexa- and heptaethylene glycol (EO6 and EO7, respectively) complexes contain discreet ions. In these halide complexes, EO7 is the only PEG to expand the Pb2+ coordination number from eight to nine. [PbBr(EO5)(μ-Br)PbBr2]·H2O is triclinic P1̄, with a = 7.922(6) Å, b = 15.802(9) Å, c = 19.001(9) Å, α = 73.19(8)°, β = 88.91(9)°, γ = 87.22(9)°, and Z = 4. [PbBr(NCMe)(EO6)]2[PbBr2(EO6)][PbBr3]2 is monoclinic P21/c, with a = 14.389(4) Å, b = 31.931(9) Å, c = 8.029(2) Å, β = 97.76(3)°, and Z = 2. [PbBr(EO7)][PbBr3] is monoclinic Cc, with a = 13.165(3) Å, b = 24.732(5) Å, c = 8.007(1) Å, β = 94.58(2)°, and Z = 4.