Two chiral Co and Ni complexes with identical ligands presenting different nonlinear optical responses

Using NaN 3 and a chiral N-donor ligand (1 R ,2 R )-1,2-diphenylethylenediamine (L) to react with Co(ClO 4 ) 2 (H 2 O) 6 and Ni(ClO 4 ) 2 (H 2 O) 6 , respectively, two chiral Co III and Ni II complexes with formulae [Co(L) 2 (N 3 ) 2 ](ClO 4 )(0.5H 2 O) ( 1 ) and [Ni(L) 2 (μ 1,3 -N 3 )] n (ClO 4 ) n (0.5H 2 O) n ( 2 ) were isolated and structurally characterized. Although 1 and 2 contain the same L and N 3 − ligands, they have completely different molecular structures. 1 shows a chiral mononuclear structure with N 3 − as the terminal ligand, in which the Co II ion has been oxidized to the Co III ion, while 2 exhibits a chiral one-dimensional (1D) Ni II chain structure with N 3 − as the bridging ligand. Notably, a study of their nonlinear optical (NLO) properties demonstrates that 1 presents a moderate second-harmonic generation (SHG) response (0.15 × KDP), while 2 only displays a strong third-harmonic generation (THG) response (160 × α-SiO 2 ). This interesting finding gives the first example of the complexes with the same ligands but different molecular structures showing completely different NLO responses regulated by metal ions. We demonstrate that the SHG and THG responses of the complexes can be regulated by metal ions.