Multistimuli Response Micro‐ and Nanolayers of a Coordination Polymer Based on Cu₂I₂ Chains Linked by 2‐Aminopyrazine

Abstract

A nonporous laminar coordination polymer of formula [Cu I (2-aminopyrazine)] is prepared by direct reaction between CuI and 2-aminopyrazine, two industrially available building blocks. The fine tuning of the reaction conditions allows obtaining [Cu I (2-aminopyrazine)] in micrometric and nanometric sizes with same structure and composition. Interestingly, both materials show similar reversible thermo- and pressure-luminescent response as well as reversible electrical response to volatile organic solvents such as acetic acid. X-ray diffraction studies under different conditions, temperatures and pressures, in combination with theoretical calculations allow rationalizing the physical properties of this compound and its changes under physical stimuli. Thus, the emission dramatically increases when lowering the temperature, while an enhancement of the pressure produces a decrease in the emission intensity. These observations emerge as a direct consequence of the high structural flexibility of the Cu I chains which undergo a contraction in CuCu distances as far as temperature decreases or pressure increases. However, the strong structural changes observed under high pressure lead to an unexpected effect that produces a less effective CuCu orbital overlapping that justifies the decrease in the intensity emission. This work shows the high potential of materials based on Cu I chains for new applications.

Smart composite films of nanometric thickness based on copper–iodine coordination polymers. Toward sensors

“…Both aforedescribed effects, meaning the sequential asymmetrical band-gap closure as well as the breaking of the electronic degeneracy, have their origin in a pressure-induced electronic degeneracy-rupture, which is a direct consequence of Pauli's exclusion principle, and it has been already reported by our group for other morphologically similar compounds. 13 The external hydrostatic pressure effect shortens bond-lengths within the compound (in particular within the metallic Cu chain), which tends to force different electrons to occupy the same electronic state, which is forbidden by Pauli's exclusion principle. Thus, the system electronically reacts by breaking the electronic degeneracy of some populated states to accommodate the pressure-induced forced electrons.…”

“…11 There are few studies focused on understanding the mechanisms involved in these changes. Very recently Kwon et al (2017) 12 and Conesa-Egea et al (2017) 13 have reported new CPs based on Cu( i )–I double chains undergoing reversible crystal-to-crystal structural changes from ambient to high pressures. These studies allow examining the reversibility of luminescence mechanochromism processes.…”

Metal–organic framework nanosheets (MONs): a new dimension in materials chemistry

“…90 Another interesting de-symmetrised case is a two-dimensional coordination polymer consisting of Cu 2 I 2 chains linked by 2-aminopyrazine. 91…”

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“…This strategy has been recently followed to successfully explain very interesting experimental emission effects. [25][26][27] The top panel of Fig. 3 shows the optimized geometries and the most stable configurations for CBZ ( Fig.…”