Helical ∞1[Pb2O] Chains in Polymorphs of Pb2O(C6H5COO)2

Three new lead oxide benzoates have been prepared solvothermally. In two polymorphs, 1 and 2, of Pb2O­(C6H5­COO)2, distorted Pb4O tetrahedra share edges to form helical ∞1[Pb2O] chains. Unprecedented among Pb4O-based structures, these motifs may be viewed as double helices of lead atoms surrounding the central oxygen atoms. Both right- and left-handed helices are included in each structure. Formation of the polymorphs was controlled through variation in synthetic conditions. Polymorph 1 crystallizes in the achiral, polar space group Fdd2. Polymorph 2, in P21, is a rare example of a kryptoracemate in which crystallographically independent chains of both chiralities occur in the asymmetric unit. This second polymorph is both chiral and polar, and the pseudosymmetric relationship between the helices has been examined. In Pb4O­(C6H5­COO)6 (3), discrete Pb4O tetrahedra are bridged by benzoate ligands to form a one-dimensional hybrid structure. The compounds have been further characterized via IR spectroscopy, elemental analysis, and thermogravimetric analysis. Measurement of the second-harmonic generating activity of 1 and 2 corroborates the crystallographic findings of noncentrosymmetry.