Jennifer Samson Jegan, Thomas Muthiah Packianathan
School of Chemistry, Tiruchirappalli, Tamil Nadu 620024, India.
Chem Cent J. 2013 Aug 15;7(1):139. doi: 10.1186/1752-153X-7-139.
Lead is a heavy toxic metal element in biological systems and is one of the major pollutants as a result of its widespread use in industries. In spite of its negative roles the coordination chemistry of Pb(II) complexes is a matter of interest. The N,N'-bidentate aromatic bases such as BPY,4-BPY and PHEN (BPY = 2,2'bipyridine, 4-BPY = 4,4'-dimethyl-2,2'-bipyridine, PHEN = 1,10-Phenanthroline) are widely used to build supramolecular architectures because of their excellent coordinating ability and large conjugated system that can easily form π-π interactions among their aromatic moieties. A series of novel Pb(II) complexes in concert with 5-CTPC, 5-BTPC (5-CTPC = 5-chlorothiophen-2-carboxylate, 5-BTPC = 5-bromothiophen-2-carboxylate) and corresponding bidentate chelating N.N' ligands have been synthesized and characterized.
Five new Pb (II) complexes [Pb(BPY)(5-CTPC)2] (1), [Pb(4-BPY)(5-CTPC)2] (2), [Pb2(PHEN)2(5-CTPC)4] (3), [Pb(4-BPY)(5-BTPC)2] (4) and [Pb2(PHEN)2(5-BTPC)2(ACE)2] (5) have been synthesized. Even though in all these complexes the molar ratio of Pb, carboxylate, N,N-chelating ligand are the same (1:2:1), there is a significant structural diversity. These complexes have been characterised and investigated by elemental analysis, IR, 1H-NMR,13C-NMR, TGA, and photoluminescence studies. Single crystal X-ray diffraction studies reveal that complexes (1, 2) and (4) are mononuclear while (3 and 5) are dinuclear in nature which may result from the chelating nature of the ligands, various coordination modes of the carboxylates, and the coordination geometry of the Pb(II) ions.
The observation of structures 2,4 and 3,5 show the structural changes made just chloro/bromo substituent of the thiophene ring. A detailed packing analysis has been undertaken to delineate the role of valuable non covalent interactions like X…π, H…X, (X = Cl/Br). A quadruple hydrogen bond linking the monomeric units and generating a supramolecular architecture is observed in (1). The metal bite unit comprised of PbN2C2 (i.e. Pb-N-C-C-N-Pb) is the repeating unit in all the five complexes and they have almost same geometrical parameters. This metal bite has been identified as the self assembly unit in complexes.
铅是生物系统中的一种重金属有毒元素，由于其在工业中的广泛应用，它是主要污染物之一。尽管铅有负面作用，但Pb(II)配合物的配位化学仍是一个受关注的问题。N,N'-双齿芳香碱，如BPY、4-BPY和PHEN（BPY = 2,2'-联吡啶，4-BPY = 4,4'-二甲基-2,2'-联吡啶，PHEN = 1,10-菲咯啉）因其出色的配位能力和大的共轭体系而被广泛用于构建超分子结构，该共轭体系能轻易在其芳香部分之间形成π-π相互作用。已经合成并表征了一系列与5-CTPC、5-BTPC（5-CTPC = 5-氯噻吩-2-羧酸盐，5-BTPC = 5-溴噻吩-2-羧酸盐）以及相应双齿螯合N,N'配体协同的新型Pb(II)配合物。
合成了五种新的Pb(II)配合物[Pb(BPY)(5-CTPC)2] (1)、[Pb(4-BPY)(5-CTPC)2] (2)、[Pb2(PHEN)2(5-CTPC)4] (3)、[Pb(4-BPY)(5-BTPC)2] (4) 和 [Pb2(PHEN)2(5-BTPC)2(ACE)2] (5)。尽管在所有这些配合物中，Pb、羧酸盐、N,N-螯合配体的摩尔比相同（1:2:1），但存在显著的结构多样性。通过元素分析、红外光谱、1H-核磁共振、13C-核磁共振、热重分析和光致发光研究对这些配合物进行了表征和研究。单晶X射线衍射研究表明，配合物(1, 2)和(4)是单核的，而(3和5)本质上是双核的，这可能是由于配体的螯合性质、羧酸盐的各种配位模式以及Pb(II)离子的配位几何结构所致。
对结构2、4和3、5的观察表明，仅噻吩环的氯/溴取代基就导致了结构变化。已经进行了详细的堆积分析，以描述诸如X…π、H…X（X = Cl/Br）等重要非共价相互作用的作用。在(1)中观察到一个四重氢键连接单体单元并形成超分子结构。由PbN2C2（即Pb-N-C-C-N-Pb）组成的金属咬合单元是所有五种配合物中的重复单元，并且它们具有几乎相同的几何参数。这种金属咬合已被确定为配合物中的自组装单元。
