Assembly of Binuclear, Tetranuclear, and Multinuclear Complexes from Pincer-Like Mononuclear Metallotectons: Structural Diversity Dependent on Precursors

Reactions
of Cu­(II), Cd­(II), and Ni­(II) with a new tetradentate ligand N1,N3-bis­(1-(1H-benzimidazol-2-yl)­ethylidene)­propane-1,3-diamine
(H2bbepd) afforded four mononuclear pincer-like complexes
of [Cu­(H2bbepd)­(ClO4)]­·CH3OH·ClO4 (1), [Cd­(H2bbepd)­(CH3OH)­(ClO4)]­·CH3OH·ClO4 (2), [Ni­(H2bbepd)­(H2O)2]­·2ClO4 (3), and [Ni­(H2bbepd)­(NO3)2] (4), respectively. The labile small coordinated
components (anions or solvent molecules) on the apical coordination
site of metal ions in complexes 1–4 display three different modes, which can be substituted by 4,4′-bipyridine
(bpy) to obtain four new multinuclear complexes of [Cu2(H2bbepd)2­(bpy)]2­·4ClO4 (5), [Cd4(H2bbepd)4­(bpy)3­(ClO4)2]­·6ClO4·(bpy)­·2CH3OH­·6H2O (6), {[Ni­(H2bbepd)­(bpy)]­·2ClO4­·CH3OH}n (7), and {[Ni
(H2bbepd)­(bpy)]­·2NO3­·CH3OH­·H2O}n (8), respectively. Complex 5 is a binuclear
dumbbell-like molecule, complex 6 is a rare example of
discrete linear tetranuclear molecule, while complexes 7 and 8 are one-dimensional chains formed by an alternate
arrangement of bpy molecules and mononuclear subunits. The differences
in complexes 5–8 are largely dependent
on the structure of the mononuclear precusors of complexes 1–4. All eight complexes are assembled into higher
dimensional supramolecular frameworks by diverse nonconvalent interactions
including unusual anion···π interactions between
perchlorate and five-membered benzimidazole rings.