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Terpyridine-Based, Flexible Tripods: From a Highly Symmetric Nanosphere to Temperature-Dependent, Irreversible, 3D Isomeric Macromolecular Nanocages Sourav Chakraborty, Wei Hong, Kevin J. Endres, Ting-Zheng Xie, Lukasz Wojtas, Charles N. Moorefield, Chrys Wesdemiotis, and George R. Newkome J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.6b11784 • Publication Date (Web): 06 Feb 2017 Downloaded from http://pubs.acs.org on February 7, 2017
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Journal of the American Chemical Society
Terpyridine-Based, Flexible Tripods: From a Highly Symmetric Nanosphere to Temperature-Dependent, Irreversible, 3D Isomeric Macromolecular Nanocages Sourav Chakraborty,a† Wei Hong,a† Kevin J. Endres,a Ting-Zheng Xie,a Lukasz Wojtas,c Charles N. Moorefield,d Chrys Wesdemiotis,*a,b and George R. Newkome*a,b a
Department of Polymer Science and bDepartment of Chemistry, The University of Akron, Akron, OH 44256. c Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620. d Dendronex, LLC, 3410 98th St., Ste 4 – 156, Lubbock, TX 79423
ABSTRACT A three-dimensional, highly symmetric sphere-like nanocage was synthesized using a terpyridine (tpy) based, flexible trisdentate ligand and characterized by single crystal X-ray analysis. To introduce more rigidity, one of the tpy units of the trisdentate ligand was pre-blocked by stable connectivity to form the corresponding Ru2+-dimer. The complexation between Ru2+-dimer and Fe2+ demonstrates an unexpected temperature-dependent assembly between two irreversible isomeric 3D nanocages. Investigation of the coordination process and structural configurations of the metal-ligand framework, affected by the introduction of rigidity and in the presence of external stimuli (temperature), is reported. INTRODUCTION Naturally occurring biological systems often utilize non-covalent supramolecular interactions to self-assemble into higher order architectures, such as the secondary and tertiary structures of proteins and DNA.1,2 The positioning and directionality of these non-covalent interactions are essential for molecular recognition and formation of supramolecular assemblies.3 Inspired by diverse systems, many efforts have been dedicated to the synthesis of complex metallosupramolecules, using metal-ligand coordination with its structural diversity. This can be realized by precise control over functional directionality of monomers with predefined bite angles.4-24 Of the numerous examples, 2,2':6',2"-terpyridine (tpy) tectons have gained extensive attention due to their ability to coordinate diverse metals that facilitate both labile (Zn2+, Cd2+) and non-labile (Ru2+, Fe2+, Os2+) ligand-metal-ligand connectivity, thus permitting control over bond strength and ultimately the desired molecular architecture(s).7,25-29 Use of linear coordinated pseudo-octahedral connectivity provides convenient synthetic characteristics to generate the edges of discrete 2D and 3D macromolecules with highly ordered organic vertices. Using tailored tpy-based monomers, we have reported the synthesis of several 1 ACS Paragon Plus Environment
Journal of the American Chemical Society
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unique 2D metallomacrocycles (including triangles,30 hexagons,31 various spoked wheels,32,33 a Sierpiński gasket34 and triangle,35 a molecular [4]-triangulane36) as well as a 3D nanosphere37 and more recently precise molecular fusion and fission between cuboctahedron and octahedron motifs.38,39 However, there are few 3D molecular cages, based on terpyridinyl ligands so far reported.37-45 Considering the potential of terpyridine-based materials for biomedical applications46,47 and optoelectronic devices,47-50 the attraction to construct new 3D-terpyridinyl nanoarchitectures is compelling. The formation of terpyridine-based nanostructures is a consequence of both kinetic and thermodynamic control; studies show that kinetically dominated complexation increases in the order Cd2+
