Deprotonation-induced enantioselective aggregation and deprotonation-induced ligand rearrangement of copper(II) complexes yield 1D homochiral and heterochiral chains and a cyclic tetramer, respectively

The copper(II) complexes of protonated pentadentate Schiff-base ligands wit h [Cu(H2Ln)](ClO4)(2) formula (n = 3-6, 3-6) have been synthesized and char acterized (H2L3 = N-((2-methylimidazol-4-yl)methylene)-3-aminpropyl-N'-((2- methylimidazol-4-yl)methylene)-4'-aminobutylamine, H2L4 = N-((2-phenylimida zol-4-yl)methylene)-3-aminpropyl-N'-((2-phenyl-imidazol-4-yl)methylene)-4'- aminobutylamine, H2L5 = N,N'-bis((2-phenylimidazol-4-yl)methylene)-3,3'-dia minodipropylmethylamine, H2L6 = N-((2-methylimidazol-4-yl)methylene)-2-amin oethyl-N'-((2-methylimidazol-4-yl)methylene)-3'-aminopropylamine. The mono- deprotonated complexes 3', 4', and 5' contain one imidazole and one imidazo late groups per unit and are Delta (clockwise) or Lambda (anticlockwise) en antiomorphs due to the spiral arrangement of the ligand around copper(II) i on. They function as chiral building components for a self-assembly process resulting from the formation of hydrogen bonds between the imidazole and i midazolate groups of adjacent units to yield 1D zigzag-chain structures. Th e distance between hydrogen-bonded nitrogen atoms is 2.81(2), 2.832(9), and 2.875(9) Angstrom for 3', 4', and 5', respectively. The crystal lattice of 3' yielded either ...Delta Delta Delta... or ...Lambda Lambda Lambda... is otactic 1D zigzag-chains, while the crystal lattices of 4' and 5' yielded . ..Delta Lambda Delta Lambda... syndiotactic 1D zigzag-chains. In 3', two ad jacent methyl groups at the 2-position connected by hydrogen bond array in the same direction, thus allowing homochiral aggregation of the complex mol ecules in a 1D chain. On the other hand, in 4' and 5', two adjacent bulky p henyl groups require opposite orientations, thus allowing heterochiral aggr egation. Enantioselective aggregation with homochirality or heterochirality can thus be controlled with suitable substituents. While its mononuclear p recursor 6 is pentacoordinated with the N-5 donor set of the pentadentate l igand H2L6, the deprotonated complex 6' has an imidazolate-bridged tetranuc lear cyclic structure with a Cu-Cu distance of 6.086(2) Angstrom. The ligan d in 6' is tetradentate and includes an hexahydropyrimidine ring resulting from a deprotonation induced rearrangement reaction.