High electrical conductivity and high porosity in a Guest@MOF material: evidence of TCNQ ordering within Cu₃BTC₂ micropores

Abstract

The host–guest system TCNQ@Cu3BTC2 is a striking example of how semiconductivity can be introduced by guest incorporation in an otherwise insulating parent material.

Micro-spectroscopy of HKUST-1 metal–organic framework crystals loaded with tetracyanoquinodimethane: effects of water on host–guest chemistry and electrical conductivity

“…3 shows the micrographs of the crystals of pristine HKUST-1 and the TCNQ@HKUST-1 host-guest composite material. In line with previous experiments, a Cu-TCNQ coordination polymer 26 can be seen at the surface of the TCNQ@HKUST-1 host-guest composite material. The bands corresponding to both materials were present after deconvolution of the average Raman spectra of each cluster (see Fig.…”

“…It is worth mentioning that the conductivity measurements were carried out using mm-sized Cu 3 BTC 2 powders (10-20 mm octahedra) infiltrated with TCNQ, as previously described in the literature. 26 However, we believe that the redispersion phenomenon may also be present in the case of those powdered samples. Previous studies have suggested that TCNQ, aligned within the pores of HKUST-1, leads to a percolation system through which electrons can hop from one pore to the next one.…”

“…The two materials under study, namely large crystals of HKUST-1 and TCNQ@HKUST-1, were obtained by a method described in a previous report by Schneider et al, 26 in which their crystallinity, morphology and porosity are reported. TCNQ was introduced by vapour phase infiltration in an evacuated glass ampoule.…”

“…in opposite sides of the pore cage, metal nodes, as evidenced by the increasing intensity of the (111) reflection in the X-ray diffraction data. 26 In addition, physisorbed TCNQ fills the remaining pore space and weakly interacts with the MOF. This leads to loadings reaching up to two TCNQ molecules per large pore, while maintaining pore space accessible for small molecules, as shown by sorption experiments with N 2 and H 2 O.…”

“…While theory predicted the coordination of TCNQ to two adjacent metal nodes of HKUST-1, 19 just recently, some of us found crystallographic evidence for this preferential adsorption, when TCNQ was introduced via the vapor phase. 26 Given the complexity of the system, elaborate characterization techniques are necessary to identify the necessary structure-property relationships and to study how moisture affects the distribution of TCNQ within the MOF and impacts the electroconductivity of the host-guest material.…”