Thermal evolution and crystal structure of a polymeric complex: Pb3(3,5-dicarboxylatopyrazole)2(NO3)2$4H2O

Pb3(pdc)2(NO3)2$4H2O (pdcZdeprotonated 3,5-pyrazole-dicarboxylic acid) has been prepared and is stable up to 100 8C. Above this temperature the hydration water loss is noted before 200 8C. Until 360 8C the material becomes amorphous during the decomposition of the organic ligand; at 365 8C crystallization occurs and can be formulated as a mixture of PbO and lead oxynitrates, which subsequently recombines between 395 and 445 8C into Pb6O5(NO3)% 2 over 570 8C, the residue is essentially red PbO. Pb3(pdc)2(NO3)2$4H2O crystallizes in the monoclinic system, aZ20.3688(7), bZ6.4232(4), and cZ18.1059(7) A° , bZ118.44(1)8, space group C2/c, ZZ4. The structure displays an original polymeric coordination complex where the lead(II) is found in two different environments: (–Pb2–pdc–)N chains are identified along the [001] direction, while inter chains Pb2–pdc and Pb1–pdc links are bridging these chains in a layer like tridimensionnal structure, where pdc is acting as an hexadentate ligand. q 2004 Elsevier B.V. All rights reserved.