Multistimuli Response Micro- and Nanolayers of a Coordination Polymer Based on Cu₂ I₂ Chains Linked by...

A nonporous laminar coordination polymer of formula [Cu₂ I₂ (2-aminopyrazine)]_n is prepared by direct reaction between CuI and 2-aminopyrazine, two industrially available building blocks. The fine tuning of the reaction conditions allows obtaining [Cu₂ I₂ (2-aminopyrazine)]_n 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 Cu₂ I₂ 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 Cu₂ I₂ chains for new applications.