title: Syntheses and characterization of two novel tetranuclear lead(II) clusters self-assembled by hydrogen bonded interactions.
abstract: BACKGROUND
  The usage of polynuclear metal clusters as secondary building units (SBU's) in designing of metal organic frameworks (MOF's) is a field of current interest. These metal clusters have attracted a great deal of attention not only due to their interesting structural topologies but also due to promising physical and chemical properties. In this regard various d,f block (transition and lanthanide) metal clusters have been widely investigated so far. Less attention is paid to construction of heavy p-block Pb(II) clusters.
  
  
  RESULTS
  Two mixed ligand Pb(II) clusters have been synthesized with bipy(2,2'-Bipyridine), phen(1,10-Phenanthroline), quin (8-Hydroxy quinolinate) and 5-tpc (5-chloro thiophene 2-carboxylate). They have been characterized by elemental analysis, IR, TGA and X-ray crystallography. X-ray diffraction analysis reveals that the complexes [Pb4(quin)4(bipy)2(5-tpc)4] (1) and [Pb4(quin) 4(phen) 2(5-tpc)4] (2) are tetranuclear. The complexes show a slight variation in unit cell parameters, due to the replacement of bipy and the phen ligands. Both complexes contain two types of Pb(II) ions which differ in the coordination geometry around the Pb(II) ion.
  
  
  CONCLUSIONS
  In both complexes the four lead ions Pb1,Pb2, Pb1(i) and Pb2(i) lie on the same plane bridged by the 5-tpc anions. Pb1 and Pb2 of both complexes contain a 5-tpc and quin coordinated in a bidentate chelating bridging fashion. In addition the Pb2 and Pb2(i) ions alone contain a bipy and phen in a bidentate chelating fashion in (1) and (2) respectively. An additional notable feature in both of these complexes are the bridging ability of the quin oxygen which forms a network of coordination bonds in between the four Pb(II) ions. In both complexes the individual units are self-assembled by C-H---Cl/C-H---S hydrogen bonding interactions to generate 2-D aggregates.
authors.affiliation: School of Chemistry, Tiruchirappalli 620024 Tamil Nadu, India.
authors.forename: Samson Jegan
authors.initials: SJ
authors.lastname: Jennifer
authors.affiliation: School of Chemistry, Tiruchirappalli 620024 Tamil Nadu, India.
authors.forename: Packianathan
authors.initials: P
authors.lastname: Thomas Muthiah
keywords: 5-chloro thiophene 2-carboxylic acid; Halogen involved hydrogen bonding; Pb(II) clusters; Pb(II) complex