Ordered 2D and 3D Polymers
Motivation:
Ordered 2D and 3D polymers (OPs; commonly referred to as covalent and metal organic frameworks, COFs and MOFs) are emergent classes of crystalline, highly porous, molecule-based materials. These can be prepared in different topologies, are readily modified post-assembly, and have been exploited for numerous applications ranging from gas storage to catalysis. Conductive OPs are of enormous interest for a series of applications where low conductivities severely limit function, such as electrical energy storage, resistive sensing, thermoelectrics, photovoltaics, or electrocatalysis. However, conductivity measurements of bulk OPs, for example using pressed pellets (or single-crystals), are typically plagued by atomic-level defects (different redox states, missing/non-bonded building blocks, impurities), grain boundary, crystallite orientation, and percolation effects, as well as probe contact issues that can obfuscate the identification of structure-property relationships. New synthetic and characterization strategies are needed to drive advances in this expansive field.
Figure 1. Ordered polymers with different 2D and 3D topologies can be prepared by careful choice of molecular building blocks.
OUR INITIAL RESEARCH DIRECTION(S):
Metal (IV) tetraaryl complexes as redox-active tetrahedral nodes. Common tetratopic linkers used to prepare OPs are based on tetraphenylmethane and silane cores, M(aryl)4 (where M = C, Si), which suffer from broken π-conjugation through the central atom. We hypothesize that by replacing this atom with a transition metal, we may improve electronic coupling between the phenyl rings and introduce accessible redox states that might serve to enhance the conductivity of structurally analogous extended materials. We have recently developed improved synthetic routes to redox-active, panchromatic Os(aryl)4 complexes, which we can now obtain in ≤76% yields from reactions between aryl Grignard reagents and non-hazardous (Oct4N)2[OsBr6] precursors (Fig. 2). We are currently evaluating different approaches to access functionalized analogues through a combination of pre- and post-assembly ligand modification strategies. Efforts to evaluate the electronic properties of these modular tetrahedral nodes comprising different central atoms is underway.
Figure 2. Our recently developed improved route to Os(aryl)4 complexes.
Key techniques (* = project dependent):
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Molecular synthesis
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Air-free chemistry (glovebox, Schlenk line)
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Single-crystal and powder X-ray diffraction
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Solution voltammetry
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Spectroelectrochemistry
Relevant Inkpen lab publications:
(1) "Pushing steric limits in osmium(IV) tetraaryl complexes" J. M. Parr, C. Olivar, T. Saal, R. Haiges, and M, S. Inkpen,* Dalton Trans., 2022, 51, 10558-10570 [article] [ChemRxiv].
Other useful references:
(1) S.U. Koschmieder, G. Wilkinson, "Homoleptic and related aryls of transition metals" Polyhedron, 1991, 10, 135–173. (2) L.S. Xie, G. Skorupskii, M. Dincă, "Electrically Conductive Metal–Organic Frameworks" Chem. Rev., 2020, 120, 8536–8580. (2) K. Geng, T. He, R. Liu, S. Dalapati, K.T. Tan, Z. Li, S. Tao, Y. Gong, Q. Jiang, D. Jiang, "Covalent Organic Frameworks: Design, Synthesis, and Functions" Chem. Rev., 2020, 120, 8814–8933.