Tunable Proton Conductivity and Color in a Nonporous Coordination Polymer via Lattice Accommodation to Small Molecules

Abstract

Nonporous coordination polymers (npCPs) able to accommodate molecules through internal lattice reorganization are uncommon materials with applications in sensing and selective gas adsorption. Proton conduction, extensively studied in the analogue metal-organic frameworks under high-humidity conditions, is however largely unexplored in spite of the opportunities provided by the particular sensitivity of npCPs to lattice perturbations. Here, AC admittance spectroscopy is used to unveil the mechanism behind charge transport in the nonporous 1•2CH 3 CN. The conductance in the crystals is found to be of protonic origin. A vehicle mechanism is triggered by the dynamics of the weakly coupled acetonitrile molecules in the lattice that can be maintained by a combination of thermal cycles, even at low humidity levels. An analogue 1•pyrrole npCP is formed by in situ exchange of these weakly bound acetonitrile molecules by pyrrole. The color and conduction properties are determined by the molecules weakly bonded in the lattice. This is the first example of acetonitrile-mediated proton transport in an npCP showing distinct optical response to different molecules. These findings open the door to the design of switchable protonic conductors and capacitive sensors working at low humidity levels and with selectivity to different molecules.

Hidden ordered structure in the archetypical Fe(pyrazine)[Pt(CN)4] spin-crossover porous coordination compound

“…2 This combination opened a vast playground of possibilities for applications in fields like gas capture 3 or chemical sensing, 4 since SCO can both modulate the interaction with the guest molecule and be modulated by the interaction with an adsorbed molecule. [5][6][7][8][9] An archetypical example of this class of compounds is the family Fe(pyrazine)[M II (CN) 4 ] (where M II is a metal in open square-planar configuration, namely Pt, Pd, Ni). 10,11 Based on the classical Hofmann clathrate compounds, 12 these threedimensional frameworks present, together with the mentioned combination of porosity and SCO, 13,14 an extremely rich display of functional properties.…”

Vapochromic effect in switchable molecular-based spin crossover compounds

“…1–3 Therefore, an essential task is to develop materials capable of responding to the presence of such hazardous chemical species in a measurable and reproducible way. 4–6 In particular, vapochromic materials ( i.e. materials undergoing colour changes due to the presence of other molecules in the gaseous state) are very appealing for the developing of sensing devices because their colour change is easily detectable by the bare-eye or through simple spectroscopic techniques.…”

Hidden ordered structure in the archetypical Fe(pyrazine)[Pt(CN)4 ] spin-crossover porous coordination compound

“…2 This combination opened a vast playground of possibilities for applications in fields like gas capture 3 or chemical sensing, 4 since SCO can both modulate the interaction with the guest molecule and be modulated by the interaction with an adsorbed molecule. [5][6][7][8][9] An archetypical example of this class of compounds is the family Fe(pyrazine)[M II (CN)4] (where M II is a metal in open square-planar configuration, namely Pt, Pd, Ni). 10,11 Based on the classical Hofmann clathrate compounds, 12 these three-dimensional frameworks present, together with the mentioned combination of porosity and SCO, 13,14 an extremely rich display of functional properties.…”