Tuning electronic properties of conductive 2D layered metal–organic frameworks via host–guest interactions: Dioxygen as an electroactive chemical stimuli

Mohammad R Momeni,Farnaz A Shakib,Zeyu Zhang,David Dell’Angelo

doi:10.1063/5.0049317

Mohammad R Momeni, Farnaz A Shakib + Show 2 more

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https://doi.org/10.1063/5.0049317

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Journal: APL materials	Publication Date: May 1, 2021
Citations: 7	License type: cc-by

Affiliation: New Jersey Institute of Technology

Abstract

Thermodynamics and kinetics of O2 adsorption and its impacts on structural features and conductive behavior of 2D π-stacked layered metal–organic frameworks (MOFs) are studied using periodic PBE-D3 quantum mechanical calculations. Our computed O2 adsorption energies of Co3(HTTP)2 (HTTP = hexathiotriphenylene), as a representative of the 2D MOFs family, show that not only open-Co(II) sites but also redox-active HTTP linkers take part in chemisorption of O2 by forming strong S=O bonds. This is in contrast to conventional 3D Co2(OH)2(BBTA) and Fe2(dobdc) MOFs with similar hexagonal 1D channels where O2 adsorption occurs solely via coordination to the open-metal sites. Due to the adsorptive capability of its redox-active linkers, Co3(HTTP)2 is superior to the analogues 3D MOFs where the change in the oxidation state of the transition metal centers is suggested to result in hindering both the kinetics and thermodynamics of the adsorption process. Our calculated band structures and density of states show that the conductive behavior of the studied Co3(HTTP)2 2D MOF changes dramatically from metallic in the parent system to semiconducting under oxygen rich conditions, with direct bandgap openings that range from 123 to 251 meV. The results presented in this work are helpful in understanding the effects of different electroactive guest molecules on the structure and conductive behavior of 2D layered MOFs and related nonporous materials.

Highlights

IntroductionMetal–organic frameworks (MOFs) are a promising class of porous hybrid organic/inorganic materials with a wide variety of applications in energy storage and conversion, catalysis, carbon capture and sequestrations, as well as water harvesting and purification. Combining the exceptional thermal, chemical, and mechanical stability of MOFs with their tunable chemical environments allows selective uptake and retention/storage of gas molecules, turning them into excellent materials for adsorption, storage, and controlled release of different adsorbates under a variety of operating conditions. MOFs with open-metal sites are suited for adsorptive separation of different gaseous mixtures depending on the strength of the coordinative bonds formed between the adsorbate molecules and the open-metal sites. Among different adsorbates, studying O2 adsorption as an electroactive chemical stimulus is of an utmost importance as traces of oxygen can alter the crystal morphology of the studied material and its electrical properties significantly
Four different O2 bound isomers were found for the 2D layered Co3(HTTP)2 Metal–organic frameworks (MOFs) due to the affinity of open-Co sites and thio functional groups of HTTP linkers for adsorbing oxygen (Fig. 2)
This is in contrast to Co3(HHTP)2, HHTP = hexahydroxytriphenylene, with only one mode of O2 adsorption, which is through coordination to the open-Co site (2D-Co in Fig. 2) with an exothermic adsorption energy (ΔEads) of −19.2 kcal/mol

Summary

Introduction

Metal–organic frameworks (MOFs) are a promising class of porous hybrid organic/inorganic materials with a wide variety of applications in energy storage and conversion, catalysis, carbon capture and sequestrations, as well as water harvesting and purification. Combining the exceptional thermal, chemical, and mechanical stability of MOFs with their tunable chemical environments allows selective uptake and retention/storage of gas molecules, turning them into excellent materials for adsorption, storage, and controlled release of different adsorbates under a variety of operating conditions. MOFs with open-metal sites are suited for adsorptive separation of different gaseous mixtures depending on the strength of the coordinative bonds formed between the adsorbate molecules and the open-metal sites. Among different adsorbates, studying O2 adsorption as an electroactive chemical stimulus is of an utmost importance as traces of oxygen can alter the crystal morphology of the studied material and its electrical properties significantly. Chemical, and mechanical stability of MOFs with their tunable chemical environments allows selective uptake and retention/storage of gas molecules, turning them into excellent materials for adsorption, storage, and controlled release of different adsorbates under a variety of operating conditions.. MOFs with open-metal sites are suited for adsorptive separation of different gaseous mixtures depending on the strength of the coordinative bonds formed between the adsorbate molecules and the open-metal sites.. Dou et al have recently shown that the presence of O2 is necessary for the synthesis of microcrystalline 2D electrically conductive M3(HIB), HIB = hexaiminobenzene and M = Ni and Cu, while in the absence of air, only amorphous gray powders would form instead..

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