Lead(II) chloride

Lead(II) chloride (PbCl2) is an inorganic compound which is a white solid under ambient conditions. It is poorly soluble in water. Lead(II) chloride is one of the most important lead-based reagents. It also occurs naturally in the form of the mineral cotunnite.
Structure and properties.
In solid PbCl2, each lead ion is coordinated by nine chloride ions in a tricapped triangular prism formation — six lie at the vertices of a triangular prism and three lie beyond the centers of each rectangular prism face. The 9 chloride ions are not equidistant from the central lead atom, 7 lie at 280–309 pm and 2 at 370 pm. PbCl2 forms white orthorhombic needles.
In the gas phase, PbCl2 molecules have a bent structure with the Cl–Pb–Cl angle being 98° and each Pb–-Cl bond distance being 2.44 Å. Such PbCl2 is emitted from internal combustion engines that use ethylene chloride-tetraethyllead additives for antiknock purposes.
PbCl2 is sparingly soluble in water, solubility product "K"sp = at 20 °C. It is one of only 5 commonly water-insoluble chlorides, the other 4 being thallium(I) chloride, silver chloride (AgCl) with "K"sp = , copper(I) chloride (CuCl) with "K"sp = and mercury(I) chloride (Hg2Cl2) with "K"sp = .
Occurrence.
PbCl2 occurs naturally in the form of the mineral cotunnite. It is colorless, white, yellow, or green with a density of 5.3–5.8 g/cm3. The hardness on the Mohs scale is 1.5–2. The crystal structure is orthorhombic dipyramidal and the point group is 2/m 2/m 2/m. Each Pb has a coordination number of 9. Cotunnite occurs near volcanoes: Vesuvius, Italy; Tarapacá, Chile; and Tolbachik, Russia.
Synthesis.
Double displacement/Metathesis.
Lead(II) chloride precipitates upon addition of aqueous chloride sources (HCl, NaCl, KCl) to lead(II) compounds
Direct Reduction.
PbCl2 can be formed by the reduction of copper(II) chloride by lead metal:
Direct chlorination.
PbCl2 also forms by the action of chlorine gas on lead metal:
Reactions.
Addition of chloride ions to a suspension of PbCl2 gives rise to soluble complex ions. In these reactions the additional chloride (or other ligands) break up the chloride bridges that comprise the polymeric framework of solid PbCl2(s).
PbCl2 reacts with molten NaNO2 to give PbO:
PbCl2 is used in synthesis of lead(IV) chloride (PbCl4): Cl2 is bubbled through a saturated solution of PbCl2 in aqueous NH4Cl forming [NH4]2[PbCl6]. The latter is reacted with cold concentrated sulfuric acid (H2SO4) forming PbCl4 as an oil.
Lead(II) chloride is the main precursor for organometallic derivatives of lead, such as plumbocenes. The usual alkylating agents are employed, including Grignard reagents and organolithium compounds:
These reactions produce derivatives that are more similar to organosilicon compounds, "i.e." that Pb(II) tends to disproportionate upon alkylation.
PbCl2 can be used to produce PbO2 by treating it with sodium hypochlorite (NaClO), forming a reddish-brown precipitate of PbO2.
Toxicity.
Like other soluble lead compounds, exposure to PbCl2 may cause lead poisoning.