Self-assembly of Ni(II) with a chiral ligand pair vs . mixture of the chiral ligand pair: structural features and recognition ability of Ni 2 L 4 cages.

The self-assembly of NiCl 2 with a chiral bidentate ligand pair, (1 R ,2 S )-(+)- and (1 S ,2 R )-(-)-1-(nicotinamido)-2,3-dihydro-1 H -inden-2-yl nicotinate ( r , s -L and s , r -L) in a mixture of ethanol and dioxane, gives rise to stable crystals consisting of [2Cl@Ni 2 Cl 2 ( s , r -L) 4 (H 2 O) 2 ]·4C 4 H 8 O 2 ·EtOH and [2Cl@Ni 2 Cl 2 ( r , s -L) 4 (H 2 O) 2 ]·4C 4 H 8 O 2 ·EtOH chiral cages, respectively, with two encapsulated chloride anions in the cavities. The most interesting feature is that the self-assembly of NiCl 2 with the mixture of r , s -L and s , r -L (1 : 1-1 : 4) produces crystals of thermodynamically stable achiral cages, [2Cl·2H 2 O@Ni 2 Cl 2 ( s , r -L) 2 ( r , s -L) 2 (H 2 O) 2 ]·7C 4 H 8 O 2 , in the molar ratio range. Furthermore, the [2Cl@Ni 2 Cl 2 ( s , r -L) 4 (H 2 O) 2 ]·4C 4 H 8 O 2 ·EtOH and [2Cl@Ni 2 Cl 2 ( r , s -L) 4 (H 2 O) 2 ]·4C 4 H 8 O 2 ·EtOH chiral crystals can recognize the pairs of L-,D-tryptophan and L-,D-cysteine via cyclic voltammetry (CV) signals, in contrast to the [2Cl·2H 2 O@Ni 2 Cl 2 ( s , r -L) 2 ( r , s -L) 2 (H 2 O) 2 ]·7C 4 H 8 O 2 achiral crystal.