MOLECULAR ADDUCTS OF INORGANIC SALTS .3. NONCENTROSYMMETRIC 3PB(REO4)(2).2TU.2H(2)O (TU=THIOUREA)

The non-centrosymmetric three-dimensional framework structure of lead perrhenate thiourea hydrate (space group P (4) over bar 2(1)m), [{Pb(R eO4)(2)}(3)(CH4N2S)(2)].2H(2)O, is built up of two types of chains run ning along the c axis: [Pb(ReO4)(4)] and [Pb-2(ReO4)(2)tu(2)](H2O)(2) (tu = thiourea). In the first type the Pb atom at the inversion point of the (4) over bar axis is surrounded by a highly regular dodecahedro n of two tetrads of ReO2 groups, forming M-T-M (M = Pb, T = ReO4) brid ges. The second type of chain has mm2 symmetry and consists of (PbO7S2 )(2) bipolyhedra with a common quadratic face of c-repeated pairs of R eO4 corners; the next two O atoms in PbO7S2 are ReO4 corners from the [Pb(ReO4)(4)] chains and the last one belongs to H2O. The S atoms of t he tu molecules act as common vertices of the c-repeated lead bipolyhe dra. An interesting feature of this structure is the arrangement of tu and H2O molecules in an alternating sequence with short contacts betw een the C and O atoms [C ... O 2.89 (5) and 2.91 (5) Angstrom].