Anna V. Davis

Supramolecular assembly dynamics

Remarkable progress in the synthetic chemistry of supramolecular assemblies has created many new structural types. With the proliferation of new structures has come increasing interest in the properties and behavior of these assemblies. Does the cooperativity of constituent components lend an assembly new properties distinct from the components themselves? Do the properties of an assembly make it suitable for application as a nanovessel for new chemistries? The latter question may lead to the synthetic targeting of assemblies for specific applications. Physical study of supramolecular systems informs the evolution of new structures, which express more complex supramolecular functionality.

Self-assembly of tetrahedral and trigonal antiprismatic clusters [Fe4(L4)4] and [Fe6(L5)6] on the basis of trigonal tris-bidentate chelators.

In a one-pot reaction, the tetranuclear iron chelate complex [Fe4(L4)4] 6 was generated from benzene-1,3,5-tricarboxylic acid trichloride (4), bis-tert-butyl malonate (5a), methyllithium, and iron(II) dichloride under aerobic conditions. Alternatively, hexanuclear iron chelate complex [Fe(L5)6] 7 was formed starting from bis-para-tolyl malonate (5b) by employing identical reaction conditions to those applied for the synthesis of 6. The clusters 6 and 7 are present as racemic mixtures of homoconfigurational (delta,delta,delta,delta)/(lambda,lambda,lambda,lambda)-fac or (delta,delta,delta,delta,delta,delta)/(lambda,lambda,lambda,lambda,lambda,lambda)-fac stereoisomers. The structures of 6 and 7 were unequivocally resolved by single-crystal X-ray analyses. The all-iron(III) character of 6 and 7 was determined by Mössbauer spectroscopy.

Structural Consequences of Anionic Host-Cationic Guest Interactions in a Supramolecular Assembly

The molecular structure of the spontaneously assembled supramolecular cluster [M(4)L(6)](n-) has been explored with different metals (M = Ga(III), Fe(III), Ti(IV)) and different encapsulated guests (NEt(4)(+), BnNMe(3)(+), Cp(2)Co(+), Cp*(2)Co(+)) by X-ray crystallography. While the identity of the metal ions at the vertices of the M(4)L(6) structure is found to have little effect on the assembly structure, encapsulated guests significantly distort the size and shape of the interior cavity of the assembly. Cations on the exterior of the assembly are found to interact with the assembly through either pi-pi, cation-pi, or CH-pi interactions. In some cases, the exterior guests interact with only one assembly, but cations with the ability to form multiple pi-pi interactions are able to interact with adjacent assemblies in the crystal lattice. The solvent accessible cavity of the assembly is modeled using the rolling probe method and found to range from 253-434 A(3), depending on the encapsulated guest. On the basis of the volume of the guest and the volume of the cavity, the packing coefficient for each host-guest complex is found to range from 0.47-0.67.