Mixed-ligand complexes of Ca(II), Ba(II), Mn(II) and Pd(II) with 1,10-phenanthroline and 5-chloro thiophene 2-carboxylic acid ligands: Role of hybrid carboxylate–water clusters and ligands of crystallisation in building up of supramolecular architectures

New mixed-ligand complexes, [M2(5-TPC)4(PHEN)2(H2O)4] M = Ca (1), Ba (2), [Mn (PHEN)(Cl)(H2O)] (5-TPC)(5-TPCH)·(H2O)2 (3), [Pd (PHEN)2] (5-TPC)2(5-TPCH)2 (4) [where 5-TPC = 5-chloro thiophene 2-carboxylate, 5-TPCH = 5-chloro thiophene 2-carboxylic acid, PHEN = 1,10-phenenanthroline] have been synthesized and characterized by FT-IR, TGA and elemental analysis. X-ray diffraction analysis reveals that the complexes (1) and (2) are binuclear and isomorphous. The Ca2+ and Ba2+ ions in (1 and 2) respectively are surrounded by eight oxygen atoms in a distorted square-antiprismatic geometry. Remarkably, the increase in metal ion size from Ca2+ to Ba2+ did not affect the overall structural features. Complexes (3) and (4) are monomeric and they belong to a class of organic inorganic hybrid materials. The coordinated water molecules in complexes (1–3) play a major role in building up of supramolecular architectures. Interestingly the O–H…O interactions make a four-membered [(H2O)2O2] ring in (1 and 2) and they form six-membered [(H2O)4O2] ring in (3) with chair conformation. Structure (3) has a combination of O–H…O and O–H…Cl interactions inbetween the coordinated and uncoordinated water molecule as well as the coordinated halide ion in the formation of supramolecular skeleton. These discrete water–carboxylate hybrid rings play a major role in stabilization of crystal structure. In (4) the cationic [Pd (PHEN)2]2+ centres are linked by two 5-TPC anions and this generates helical chains forming a double helix like structure.