Fine-tuning the ring-size of metallacyclophanes: a rational approach to molecular pentagons.


The essence of supramolecular chemistry is the self-assembly of noncovalently linked molecular clusters and networks, a spontaneous process that involves various driving forces (e.g., metal-ligand interactions, ion templation, hydrogen bonding, π stacking) and chemical flexibility (i.e. facile rearrangement of the building blocks).1 In principle, if one can identify the dominant factors in a self-assembly process, they can be systematically varied to favor specific supramolecular entities. This principle is nicely illustrated by the self-assembly reactions of metal cations with bis-chelating ligands such as bptz, (3,6-bis(2-pyridyl)1,2,4,5tetrazine).2-4 Among our early findings in this chemistry was that the molecular squares [M4(bptz)4(MeCN)8] (M: Ni, Zn)4,5 form in high yields with [BF4] and [ClO4] but not with anions such as [PF6], [BPh4], and [CF3SO3]. Armed with this information, we launched a comprehensive investigation into the role of the anion in determining the products of metal/bptz reactions. The premise of the studies was that other nuclearities could be favored, provided the appropriate anion is available to act as a template. If one considers the size and shape parameters of common anions,6 [SbF6] with Vm ) 63 Å3 compared to 38 and 47 Å3 for [BF4] and [ClO4], respectively, is an excellent candidate for the formation of a slightly larger cyclic entity. On the basis of this premise, [Ni(CH3CN)6][SbF6]2 was reacted with bptz in a 1:1 ratio in acetonitrile (Scheme 1). The reaction mixture converts from the pale blue color of the Ni precursor to a brownish-green color within minutes. Crystals of the product were obtained in 60 to 70% yields by layering the reaction solution with toluene. An X-ray crystallographic study identified the new compound as [Ni5(bptz)5(CH3CN)10][SbF6]10 ([1][SbF6]10) which contains a

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@article{CamposFernndez2001FinetuningTR, title={Fine-tuning the ring-size of metallacyclophanes: a rational approach to molecular pentagons.}, author={Cristian Saul Campos-Fern{\'a}ndez and Rodolphe Cl{\'e}rac and John Koomen and David H Russell and Kim R Dunbar}, journal={Journal of the American Chemical Society}, year={2001}, volume={123 4}, pages={773-4} }