Supramolecular Chemistry of Bent Bridging Ligands

This thesis describes the investigation of the supramolecular chemistry of two closely related bent ligands 4,4'–dipyridyl ketone (L1) and 4,4'–dipyridyl ketoxime (L2) with a range of Ag(I), Cu(I) and Cu(II) salts. Chapter one introduces the field of supramolecular chemistry and crystal engineering. This chapter also covers detailed background of one-dimensional coordination polymers along with additional focus on two-dimensional coordination polymers. In order to understand the nature of interactions of L1 and L2 ligands, bent flexible and rigid ligands similar to these ligands with respect to the position of pyridine rings have been reviewed towards the end of this chapter. Chapter two reviews N–positioned isomers of dipyridyl ketones and provides a particular focus on the L1 ligand. This chapter also provides a literature review of one-dimensional coordination polymers of the Ag(I) chemistry of 4–pyridine ligands. The synthesis and characterisation of six new Ag(I)–L1 complexes are also given. The complexes {[Ag(L1)](CF3SO3).1/2H2O}∞, {[Ag(L1)2](CF3SO3).1/2H2O}∞, {[Ag(L1)](ClO4).1/2H2O}∞, {[Ag2(L1)2(CH3CN)](ClO4)2(CH3CN)2.H2O}∞, {[Ag2(L1)2(CH3CN)2](PF6)2(CH3CN)–(CH3OH)}∞, {[Ag(L1)2](BF4)}∞ were structurally characterised by single crystal X-ray diffraction. All the six complexes were meso-helical one-dimensional polymers. The role of counteranion, metal–to–ligand ratio and solvent has been studied. A comparison of the six structures is presented towards the end of the chapter. Chapter three reviews the role of coordinating and non-coordinating counteranions in the Cu(I) complexes related to this thesis. The synthesis and characterisation of four new Cu(I)–L1 complexes are also given. Both complexes {[Cu(L1)(CH3CN)2](PF6)}∞ and [Cu(L1)I]∞ formed infinite one-dimensional zigzag and daisy double-chained coordination polymers, respectively. The complexes {[Cu(L1)2](PF6)}∞ and [Cu2(L1)(SCN)2]∞ were two-dimensional sheets of varying topology. The synthesis and the structural characterisation of ligand 4,4'–dipyridyl diol (L3) and the complex {[Cu(L3)2SO4].9H2O}∞ has also been discussed. A comparison of the four Cu–L1 structures is presented towards the end of the chapter. Chapter four introduces the chemistry of oximes in general and proceeds with the description of design, synthesis and characterisation of the L2 ligand. A literature review on hydrogen-bonding interactions in Cu(I) and Cu(II) species is presented with some additional focus on stabilisation of Cu(I) complexes. The synthesis and characterisation of four Cu(I)–L2 complexes and one Cu(II)–L2 complex has been described in this chapter. The complex {[Cu(L2)2(CF3SO3)]}∞ was found to be one-dimensional polymeric chain with uncoordinated L2 side arms. The complexes {[Cu(L2)2](CF3SO3)(H2O)2}∞, {[Cu(L1)(L2)](ClO4)H2O}∞ and {[Cu(L2)2(NO3)(H2O)](NO3)(CH3OH)2(H2O)2}∞ were found to be two-dimensional sheets. The complex of {[Cu(L2)2I].2CHCl3}2 was structurally characterised and found to be a discrete species. This complex displayed strong hydrogen-bonding interactions and extended the topology to two-dimensional mosaic sheets. All five structures discussed in this chapter extended their topology by virtue of weak to strong hydrogen-bonding interactions. A comparison of the five structures is presented towards the end of the chapter