A Novel, Tunable Manganese Coordination System Based on a Flexible “Spacer” Unit: Noncovalent Templation Effects

The reaction of bis(hexafluoroacetylacetonato)manganese(II) trihydrate (2), an ∼90° corner unit,
with flexible linking unit 4,4‘-trimethylenedipyridine (1) allows for the potential formation of three different
types of solid-state coordination species:  infinite helical polymers, closed dimeric systems, and infinite one-dimensional polymers. While the un-templated starting material is known to give a coordination helix, the
other two possible species can be realized through the selective use of a variety of simple, organic guests: 
toluene (3), diphenylmethane (4), cis-stilbene (5), 1,3-diphenylpropane (6), benzyl alcohol (7), nitrobenzene
(8), and cyanobenzene (9). When solutions of 1 and 2 are crystallized in the presence of all of these clathrates,
the dimeric macrocycles result in all cases, except for that of 6, in which a syndiotactic, wedge-shaped polymer
forms. Employing a linker that is less rigid than is typically used in crystal engineering, such as 1, enables the
nucleophilic donor subunit to be more than just a simple “spacer”, instead making it an essential, tunable
component in the overall crystal lattice. In so doing, a great deal of molecular “information” is lost, but this
is compensated for by an in-depth investigation into the weaker host−guest and/or guest−guest interactions,
such as nonclassical hydrogen bonding and an assortment of hydrophobic interactions, present in the various
systems.