Controlled formation and topologies of thiophenolate-based macrocycles: rings, cylinders and bowls

The Schiff-base condensations of 1,3-diaminopropane with a protected thiophenol dialdehyde in the presence of Ni2+, Pd2+ or Zn2+ can be controlled to yield either mononuclear acyclic, or 2 + 2 and 4 + 4 macrocyclic complexes by the choice of both metal cation and counteranion. The Ni2+ complex of the 2 + 2 macrocycle contains two square-planar nickel ions and shows an arrangement similar to one observed previously: the mu-S atoms of the thiophenolate groups are pyramidal and lie on the same side of the plane defined by the four N atoms of the macrocycle to give a V-shaped molecule. By contrast, the Zn2+ complex of the 2 + 2 macrocycle undergoes oligomerisation to yield a bowl-shaped hexanuclear complex that includes a mu(3)-carbonate anion. Essential for this topology is the presence of three mu(3)-S-thiophenolato groups that link the three macrocyclic units to form a Zn3S3 ring that seals the bottom part of the bowl. In this arrangement, one of the pyramidal mu(3)-S atoms in each dinuclear Zn2+ complex is inverted relative to the arrangement observed for the dinickel complexes. Molecular modelling suggests that inversion about the mu-S atoms of the 2 + 2 macrocyclic complexes is readily accessible at room temperature and that the contrasting arrangements observed for the Ni2+ and Zn2+ complexes are those energetically most favourable for the respective metal ions. Rare 4 + 4 macrocyclic complexes are isolated as neutral dinuclear complexes for Ni2+ and Pd2+ and as a tetranuclear complex cation for Zn2+. The topologies of these systems contrast significantly: those with two square-planar Ni2+ or Pd2+ ions form extended rings, while that with Zn2+ forms a sulfur-lined cylinder which hosts acetonitrile molecules in the crystalline state. Reaction conditions can also be optimised to produce 2 + 1 acyclic ligands as their mononuclear Ni2+ and Pd2+ complexes, providing potentially useful building blocks for production of more complicated macrocyclic and supramolecular systems.