Guest–Host Complexes of TCNQ and TCNE with Cu₃(1,3,5-benzenetricarboxylate)₂

Abstract

A combined spectroscopic and structural study was undertaken to investigate the nature of the incorporation of the electron acceptor guest 7,7,8,8-tetracyanoquinodimethane (TCNQ) and the closely related guest tetracyanoethylene (TCNE) into the host porous framework [Cu 3 (BTC) 2 ] (BTC = 1,3,5-benzenetricarboxylate)a guest−host system recently shown to be highly conductive. We find that the guest concentration in the system can be modulated via the synthesis reaction time and temperature. A suite of spectroscopic, X-ray and neutron powder diffraction, and density functional theory techniques revealed the mechanism of guest binding within the framework host, including the guest redox states. This work provides insights into the way that electrical conductivity arises in porous framework host−guest systems and contributes to understanding how fine-tuning framework properties influences conductivity.

Retrofitting metal-organic frameworks

“…After introducing the general working principle of RetroFit, we applied RetroFit to the well-established Cu 3 BTC 2 system. Cu 3 BTC 2 was previously used in retrofitting experiments to obtain TCNQ@Cu 3 BTC 2 and TCNE@Cu 3 BTC 2 13,22,32 . Notably, TCNQ and TCNE as prototypical CLs exhibit four nitrile groups that are available for the coordination to OMSs; however, due to the spatial orientation of the OMSs in Cu 3 BTC 2 and size dependent restrictions given by the CL and MOF combination, only two nitrile groups coordinate to the MOF while the remaining two point to the center of the pore.…”

“…Additionally, when trying to rationalize the underlying mechanism of CL installation, diffusion limitations are expected to play a role, since diffusion pathways through the pores are successively blocked with increasing CL installation. While longer reaction times and relatively high temperatures can overcome such diffusion barriers 30,31 , vapor phase infiltration at elevated temperatures with CLs that exhibit low sublimation temperatures have proved most suitable in this context 13,30,32 . It is also interesting to note that current literature examples are limited to retrofitting with ditopic CLs 21–23,26,27,31 , with bulkier tritopic ligands further increasing concerns related to diffusion limitations.…”

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

“…No washing step is needed to remove excessive TCNQ, which is advantageous over the kinetically controlled loading procedure presented in previous studies. 8 – 10 , 16 High reaction temperatures and long exposure times evidently promote an ordered, periodic arrangement of TCNQ within the (111) crystal lattice plane and the bridging coordination motif of TCNQ and the Cu atoms of two neighbouring paddle-wheel units. To our knowledge this is the first crystallographic evidence for the integration of TCNQ into the framework of Cu 3 BTC 2 , and further demonstrates that the introduction of a non-innocent guest molecule can be regarded as a new element of MOF property design.…”

“…Recently, D'Alessandro and co-workers applied a vacuum vapor-phase infiltration (VPI) for the incorporation of TCNQ into Cu 3 BTC 2 . 16 In their approach, however, infiltrated samples were subsequently washed with solvent to remove excess, uninfiltrated TCNQ. Furthermore, samples were treated under ambient conditions, compromising efforts to keep the host–guest system free from solvent and moisture.…”

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

“…2e): one contribution arising from physically deposited TCNQ, at 2224 cm À1 , and a smaller component at 2210-2214 cm À1 , assigned to TCNQ coordinated to the Cu paddlewheels. In contrast, no clear signs of the Cu-TCNQ coordination polymer, which typically shows the CRN stretch at 2205 cm À1 , 32,37,38 were observed. It is important to bear in mind that the average spectra contain the spectral contribution of different pixels located at the edge of the crystal and other areas.…”