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

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.