Macrocycles incorporating isomeric arms: synthesis and crystal structures of ligands and their mono-, di- and polynuclear supramolecular complexes

Abstract

An isomeric series of NS₂-macrocycles containing a pyridine-arm at the ortho (o-L), meta (m-L) and para (p-L) positions were synthesized and structurally characterised by X-ray analysis. A comparative investigation of the coordination behaviour of these ligands with Ag^I, Hg^II, Pb^II and Cu^II is reported. The X-ray structures of seven complexes (1–7) have been determined, and a range of structural types and coordination modes including mono- to multinuclear and discrete to continuous ones, are shown to occur. Reactions of these ligand isomers with Ag^I salts (ClO₄⁻ and NO₃⁻) afforded four complexes (1–4): the monomer (1 : 1, metal-to-ligand) complex with a trigonal bipyramid (TBP) geometry [Ag(o-L)ClO₄] (1), the anion-free cyclic dimer (2 : 2) complex with two separated units, [Ag₂(m-L)₂]₂(ClO₄)₄ (2), the cyclic dimer complex [Ag₂(p-L)₂](ClO₄)₂·CH₃CN (3) and the unique poly(cyclic dimer) network complex {[Ag₂(p-L)₂(NO₃)]NO₃}_n (4). Three divalent metal ion (mercury, lead and copper) complexes (5–7) of o-L were also isolated: the 1 : 1 monomer complexes with a square pyramid (SP) geometry [Hg(o-L)(NO₃)₂] (5) and [Cu(o-L)(H₂O)ClO₄]ClO₄ (6) and the anion-linked dinuclear complex [Pb₂(o-L)₂(CH₃OH)₂(μ₂-ClO₄)₂](ClO₄)₂ (7), adopting a monocapped trigonal prismatic geometry. In all cases, the pyridine arms with the different nitrogen positions have an important role in their three dimensional coordination behaviours via the strong N_py-M bonds. Also their coordination patterns depend markedly on the variation of the pyridyl nitrogen positions especially for m-L and p-L due to the preference of the network formation with discrete or continuous structures.