Lead-207 chemical shift data for bivalent lead compounds: thermodynamics of the equilibrium Pb(O2CCH3)2⇌[Pb(O2CCH3)]++ O2CCH3– in aqueous solution in the temperature range 303–323 K

摘要: Lead-207 n.m.r. chemical shift data have been recorded for the following bivalent lead compounds (solvent in parentheses) : Pb(NO3)2(water), Pb(ClO4)2·3H2O (water), Pb(O2CCH3)2·3H2O Pb(O2CC6F5)2(tetrahydrofuran, thf), Pb[S2P(OR)2]2(R = C2H5 or i-C4H9)(thf and dichloromethane). The nature of solution species is discussed. very high-field shifts exhibited by hydrated lead(II) dication monoacetato- mononitrato-lead(II) monocations are ascribed to efficient nuclear shielding resulting from confinement lone pair metal 6s orbital. Chemical other occur at much lower field, structures which stereochemically active occupying a hybrid sp3dn orbital proposed. Analysis concentration-dependence has employed evaluate association constant 298 K, Kassoc., [Pb(NO3)]+(1.233 dm3 mol–1), dissociation Kdissoc., Pb(O2CCH3)2(0.0139 mol dm–3), aqueous nitrate acetate systems, respectively. Data systems Pb(O2CC6F5)2(tetrahydrofuran) Pb[S2P(OEt)2]2(dichloromethane) interpreted terms dimer ⇌ monomer equilibrium, with constants K dimer, 0.143 0.268 dm–3, concentration-independent dithiophosphoridates tetrahydrofuran formation stable thf solvate solution. Thermodynamic equilibrium Pb(O2CCH3)2⇌[Pb(O2CCH3)]++ O2CCH3– evaluated as ΔH298=–14.2 kJ mol–1, ΔG298= 10.5 ΔS298=–82.95 J K–1 mol–1.