Coordination behaviour of symmetrical hexadentate N-donor Schiff bases towards zinc(II)pseudohalides: Syntheses, crystal structures and luminescence

Two new Schiff bases, N-(1-pyridin-2-ylformylidene)-N′-[2-({2-[(1-pyridin-2-ylformylidene)amino]ethyl}amino)ethyl]ethane-1,2-diamine (L1) and N-(1-pyridin-2-ylformylidene)-N′-[2-(4-{2-[(1-pyridin-2ylformylidene)amino]ethyl}piperazin-1-yl)ethyl]amine (L2) have been prepared and used to synthesize two series of zinc(II) pseudohalide complexes of the dinuclear type [Zn2(L1/L2)(X)4] (1a–1d) (L1:X=N3-,1aand X = NCS−, 1b; L2:X=N3-,1c and X = NCS−, 1d) and the molecular ion-pair type [Zn(L1/L2)][Zn(X)4] (2a–2d) (L1:X=N3-,2a and X = NCS−, 2b; L2:X=N3-,2c and X = NCS−, 2d). Elemental, spectral and other physicochemical results are used to characterize the complexes. Single crystal X-ray diffraction studies confirm the structure of two representative members, [Zn2(L2)(N3)4] (1c) and [Zn(L1)][Zn(NCS)4] (2b). The structural analyses reveal that each zinc atom in dinuclear 1c, has a distorted trigonal bipyramidal geometry with a ZnN5 chromophore, whereas in molecular ion-pair 2b, the zinc(II) ion has a distorted octahedral environment in the cationic part with a ZnN6 chromophore and the remaining zinc(II) ion in the anioic part has a distorted tetrahedral geometry with a ZnN4 environment. All the complexes display intraligand 1(π–π∗) fluorescence and intraligand 3(π–π∗) phosphorescence in glassy solutions (77 K).

Two series of zinc(II) pseudohalide complexes of dinuclear type [Zn2(L1/L2)(X)4] (1a–1d) (L1:X=N3-,1a and X = NCS−, 1b; L2:X=N3-,1c and X = NCS−, 1d) and molecular ion-pair type [Zn(L1/L2)][Zn(X)4] (2a–2d) (L1:X=N3-,2a and X = NCS−, 2b; L2:X=N3-,2c and X = NCS−, 2d) [N-(1-pyridin-2-ylformylidene)-N′-[2-({2-[(1-pyridin-2-ylformylidene)amino]ethyl}amino)ethyl]ethane-1,2-diamine (L1) and N-(1-pyridin-2-ylformylidene)-N′-[2-(4-{2-[(1-pyridin-2ylformylidene)amino]ethyl}piperazin-1-yl)ethyl]amine (L2)] have been prepared. Single crystal X-ray diffraction studies confirm the structures of the two representative members, [Zn2(L2)(N3)4] (1c) and [Zn(L1)][Zn(NCS)4] (2b).Figure optionsDownload as PowerPoint slide