Protonmotive force: development of electrostatic drivers for synthetic molecular motors.

Ferrocene has been investigated as a platform for developing protonmotive electrostatic drivers for molecular motors. When two 3-pyridine groups are substituted to the (rapidly rotating) cyclopentadienyl (Cp) rings of ferrocene, one on each Cp, it is shown that the (Cp) eclipsed, pi-stacked rotameric conformation is preferred both in solution and in the solid state. Upon quaternization of both of the pyridines substituents, either by protonation or by alkylation, it is shown that the preferred rotameric conformation is one where the pyridinium groups are rotated away from the fully pi-stacked conformation.

Supramolecular recognition forces: an examination of weak metal-metal interactions in host-guest formation.

Molecular receptors consisting of two parallel-disposed terpy-M-Cl units (M = Pd2+, Pt2+) are used to form host-guest adducts with aromatic molecules and with neutral square-planar Pt2+ complexes. Host-guest formation is controlled by several factors including pi-pi interactions and, in some cases, weak Pt-Pt interactions between the host and the guest. This latter interaction was examined by comparing the host-guest stability of adducts formed by isoelectronic Pt2+ and Au3+ complexes with the Pt2+ receptor.

Supramolecular recognition: protonmotive-driven switches or motors?

A dicationic molecular receptor bearing two cofacially disposed terpyridyl-Pd-Cl units forms stable 1:1 host-guest complexes with planar, neutral platinum(II) complexes. When the guest is modified to incorporate a pyridine group, the now basic guest is protonated by trifluoroacetic acid in acetonitrile solutions. The basic yellow guest forms a stable, deep red 1:1 host-guest complex with the yellow palladium receptor.

Molecular recognition. Self-assembly of molecular trigonal prisms and their host-guest adducts.

Two supramolecular trigonal prisms, each bearing three molecular clefts are shown to form 1:6 and 1:7 host-guest complexes with 9-methylanthracene and one of the prisms forms a 1:2 host-guest complex with a tritopic tri-anthracene guest that registers with the recognition sites of the host.