Temperature dependent CO2 behavior in microporous 1-D channels of a metal-organic framework with multiple interaction sites

Dongwook Kim,Jaehun Park,Myoung Soo Lah,Yung Sam Kim

doi:10.1038/srep41447

Abstract

The MOF with the encapsulated CO2 molecule shows that the CO2 molecule is ligated to the unsaturated Cu(II) sites in the cage using its Lewis basic oxygen atom via an angular η1-(OA) coordination mode and also interacts with Lewis basic nitrogen atoms of the tetrazole ligands using its Lewis acidic carbon atom. Temperature dependent structure analyses indicate the simultaneous weakening of both interactions as temperature increases. Infrared spectroscopy of the MOF confirmed that the CO2 interaction with the framework is temperature dependent. The strength of the interaction is correlated to the separation of the two bending peaks of the bound CO2 rather than the frequency shift of the asymmetric stretching peak from that of free CO2. The encapsulated CO2 in the cage is weakly interacting with the framework at around ambient temperatures and can have proper orientation for wiggling out of the cage through the narrow portals so that the reversible uptake can take place. On the other hand, the CO2 in the cage is restrained at a specific orientation at 195 K since it interacts with the framework strong enough using the multiple interaction sites so that adsorption process is slightly restricted and desorption process is almost clogged.

Highlights

Recent global warming is closely related to the increased CO2 concentration in the atmosphere[1]
While there are several reports on the vibrational mode analysis of CO2 strongly bound to metal centers[13,23,24,25,26,27], only a few investigations on the correlation between the vibrational modes of the encapsulated CO2 weakly interacting with the framework and its structural data are reported[16,17,18,19,22,28,29]
A single crystal structure analysis revealed that the product is a 3-D metal-organic frameworks (MOFs) of an 8-c bcu topology[30] with linear trinuclear [Cu3Cl2] secondary building unit (SBU) as an 8-c node and tridentate tz as a ditopic linker (Fig. 2)

Summary

Introduction

Recent global warming is closely related to the increased CO2 concentration in the atmosphere[1]. Microporous metal-organic frameworks (MOFs) received great attentions for CO2 capture and utilization[6,7,8,9,10,11,12]. While there are several reports on the vibrational mode analysis of CO2 strongly bound to metal centers[13,23,24,25,26,27], only a few investigations on the correlation between the vibrational modes of the encapsulated CO2 weakly interacting with the framework and its structural data are reported[16,17,18,19,22,28,29]. We report the temperature dependent single crystal structure analyses of a microporous MOF with bound CO2 in microporous 1-D channels via both a weak angular η1-(OA) coordination of CO2 to Cu(II) sites and a dipole-quadrupole interaction between a Lewis basic atom of a framework and the Lewis acidic carbon atom of CO2. Around ambient temperatures but irreversible CO2 uptake at 195 K could be explained based on temperature dependent structural information and vibrational band analyses of the bound CO2

Methods

Results

Conclusion