Remarkably distorted M3L2 cage and M4L4 metallocyclic frameworks obtained from Ag(NO3) and bis-benzimidazole-type ligand having an NH2 group: effects of the NH2 chemical interaction site on the obtained structures

Abstract The new flexible bis-benzimidazole-type compound with an amino (NH2) group, BIm–CH2–C6Me3NH2–CH2–BIm (BIm = benzimidazole) (bbitrbNH2), was prepared as a new bridging ligand having an NH2 chemical interaction site. The ligand was obtained from mesitylene by 4-step general organic synthetic procedures. The treatment of Ag(NO3) with the bbitrbNH2 in a mixed solution of MeOH/EtOH produced [(NO3)Ag3(bbitrbNH2)2](NO3)2(H2O)6 (1), which has an M3L2 cage structure by connecting the 2 bbitrbNH2 with 3 AgI atoms. The amino group and 2 imidazole-nitrogen atoms function as the coordination sites with AgI atoms to construct the M3L2 cage. Because of the different sizes of the 2 kinds of coordination parts, i.e. an amino group and methylbenzimidazole groups, the remarkably distorted M3L2 cage framework is created. Similar reaction of Ag(NO3) with the bbitrbNH2 in an MeOH/MeCN mixed solution produced [(NO3)2Ag4(bbitrbNH2)4](NO3)2(MeOH)2 (2), which has a nano-sized M4L4 metallocyclic framework composed of 4 AgI atoms and 4 bbitrbNH2. The NH2 groups of the ligand framework form hydrogen bonds, connecting each M4L4 framework. The syntheses, molecular structures, and the unique effects of the amino group incorporated in the ligand on the obtained coordination structures are described.