Ion-pair charge transfer complex with near-IR absorption: Synthesis, crystal structure and properties of [Hb]2[Cu(mnt)2] (Hb = 1-(4-((1H-imidazol-1-yl)methyl)benzyl)-1H-imidazol-3-ium)

The compound [Hb]2[Cu(mnt)2] (1) [Hb = 1-(4-((1H-imidazol-1-yl)methyl)benzyl)-1H-imidazol-3-ium] has been synthesized, starting from 1,4-bis((1H-imidazol-1-yl)methyl)benzene, cupric chloride, and Na2mnt in methanol. Compound 1 crystallizes in monoclinic system with C2/c space group. In the crystal structure, the interactions between cations and anions via bifurcated CH···(NC-mnt)2 hydrogen bonds give rise to a two dimensional supramolecular network. It has also been observed that two cation moieties (Hb) are attached together by a very short CH···N hydrogen bonding interaction with H···N distance of 1.74 Å, ∠CHN bond angle of 174.9°. Compound 1 is additionally characterized by cyclic voltammetry, UV–Vis, IR, 1H NMR and EPR spectroscopy. The ion-pair compound 1 shows an intense absorption in the near-IR region at ∼1214 nm which has been described as a charge transfer band from HOMO of the copper dithiolate anion [Cu(mnt)2]2−, to LUMO of the [Hb]+ cation. The title compound exhibits an oxidative response at +0.46 V vs. Ag/AgCl and a reductive event at −0.67 V vs. Ag/AgCl.