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 (L-1) and N-(1-pyridin-2-ylformylidene)-N'-[2-(4-{2-[(1-pyridin-2ylformylidene)amino]ethyl}piperazin-1-yl)ethyl]amine (L-2) have been prepared and used to synthesize two series of zinc(II) pseudohalide complexes of the dinuclear type [Zn-2(L-1/L-2)(X)(4)] (1a-1d) (L-1:X = N-3(-), 1a and X = NCS-, 1b; L-2:X = N-3(-) 1c and X = NCS-, 1d) and the molecular ion-pair type [Zn(L-1/L-2)][Zn(X)(4)] (2a-2d) (L-1:X = N-3(-), 2a and X = NCS-, 2b; L-2:X = N-3(-), 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, [Zn-2(L-2)(N-3)(4)] (1c) and [Zn(L-1)][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)(pi-pi*) fluorescence and intraligand (3)(pi-pi*) phosphorescence in glassy solutions (77 K). (C) 2006 Elsevier Ltd. All rights reserved.