Copper(I) and Silver(I) 2-Methylimidazolates: Extended Isomerism, Isomerization, and Host–Guest Properties

Syntheses, structures, and properties of univalent coinage
metal
2-methylimidazolate supramolecular isomers [M­(mim)] (1, M = Cu; 2, M = Ag) were investigated in detail. In
addition to the known isomers, namely, zigzag chains [Cu­(mim)] (1a) and [Ag­(mim)] (2a), molecular octagon [Cu8(mim)8]·C6H6 (1b), decagon [Cu10(mim)10]·C8H10 (1c), helical chain [Ag4(mim)4]·C6H6 (2b), and S-shaped chain [Ag4(mim)4]·C8H10 (2c), two new structures including
a polyrotaxane [Cu10(mim)10]·[Cu­(mim)]
(1d, C2/m, a = 14.452(4) Å, b = 27.712(7) Å, c = 11.427(3) Å, β = 125.899(4)°, V = 3707(2) Å3) and a new octagon [Ag8(mim)8]·Me2CO (2d, C2/c, a = 21.852(3) Å, b = 12.101(2) Å, c = 20.907(3) Å,
β = 90.875(2)°, V = 5528(2) Å3) were discovered. The potential porous properties of guest-containing
[M­(mim)] isomers were studied by thermogravimetry, X-ray powder diffraction,
vacuum thermal desorption, and CO2 sorption experiments.
The isomers show distinctly different guest removal behaviors depending
on their pore structures. By heating, the guest-containing isomers, 1b–1c and 2b–2d, undergo irreversible, two-step, crystal-to-crystal structural
transformations to form the guest-free isomers 1a or 2a, respectively. Except 1b, other guest-containing
isomers can retain their porous structures after removal of the template
molecules, which were confirmed by CO2 sorption experiments.