Structural Diversity and Polytypism of Lead Phenylphosphonates: BING-6 and BING-9

We report the solvothermal synthesis and characterization of a series of layered lead phenylphosphonates. The crystals were suitable for single crystal X-ray diffraction data, and the two new structures we denote BING-6 [SUNY at Binghamton, Structure No. 6, Pb(PO3C6H5).0.25C5H5N, triclinic space group P1, Z= 2, a = 7.0770(4) A, b = 9.3113(6) A, c = 14.6785(9) A, a = 80.456(1)°, beta = 78.023(1)°, gamma = 73.265(1)°] and BING-9 [Pb(PO3HC6H5)(PO3HC6H4CH3), monoclinic space group C2/c, Z= 4, a = 32.663(8) A, b = 5.6220(13) A, c = 8.3307(19) A, (3 = 101.419(4)°]. The third structure, a polytype of BING-9, was previously known only from powder X-ray diffraction methods and is denoted 3 [Pb(PO3HC6H5)2, monoclinic space group C2/c, Z= 4, a = 31.681(6) A, b = 5.5639(11) A, c= 8.2515(16) A, beta = 101.814(4)°]. All three structures possess Pb(ll) and P centers connected by doubly and triply bridging oxygens. The phenyl groups cap and separate the charge-neutral layers. The phosphonates of BING-6 are nonprotonated, and the structure therefore has a Pb/P ratio of 1:1. Neutral, partially disordered pyridine solvent molecules also reside in the interlamellar space, increasing the layer to layer distance. BING-9 and 3 are polytypes and contain singly protonated phosphonates, for a Pb/P ratio of 1:2. Further characterization methods are discussed, including powder X-ray diffraction, in-situ variable temperature powder X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. Related work in the Ge, Sn, and Mn systems is also discussed. These low-dimensional materials may be useful intercalation compounds for ionexchange or sensor applications.