Copper(I) 2‑Isopropylimidazolate: Supramolecular Isomerism, Isomerization, and Luminescent Properties

Solvothermal reactions of Cu­(NO3)2 and 2-isopropylimidazole
(Hipim) in different solvents/templates gave three supramolecular
isomers: α-[Cu­(ipim)] (1), β-[Cu­(ipim)] (2), and γ-[Cu­(ipim)]·1/3C6H6 (3). Single-crystal X-ray diffraction analyses showed
that 1, 2, and 3 are parallel-packed
wavy chains, triple-stranded helices, and cubic–orthogonal-packed
helical chains consisting of alternatively interconnected two-coordinated
Cu­(I) ions and ipim– ligands. Because of the different
intermolecular interactions, 1, 2, and 3 show different phosphorescence properties with emission
maxima at 555, 540, and 530 nm, respectively. More interestingly,
[Cu­(ipim)] can melt at high temperature without decomposition. Compounds 1 and 2 melt above 185 and 146 °C, respectively;
this liquid solidifies below 117 °C to form 1 again.
However, 3 loses the benzene guest molecules above 90
°C and transforms to 1 in a crystal-to-crystal manner.