A Zinc(II) Complex Composed of a Tridentate Ligand Bearing Podand Pyrenyl Moieties

Abstract

The structural characterization and function of ZnII complexes composed of a tridentate ligand bearing podand pyrenyl moieties as a fluorophore [2,6-pyridinedicarboxaldehydebis(1-pyrenylmethylimine) (L1)] are described. The tridentate podand ligand L1 forms a 2:1 complex, [Zn(L1)2(BF4)2], with Zn(BF4)2 although the 1:1 complex [Zn(L1)(OAc)2] is obtained with Zn(OAc)2. The X-ray crystal structure determination of [Zn(L1)2(BF4)2] reveals that two tridentate podand ligands L1 coordinate meridionally to ZnII ion to give an orthogonally oriented molecular turn around the approximately octahedral ZnII center. One pyridyl moiety of L1 is sandwiched in between two podand pyrenyl moieties of another L1 through π-π interactions, together with an extended π-stacking through π-π interactions between the pyrenyl moieties in the crystal packing. [Zn(L1)(OAc)2] serves as a fluorophore metalloreceptor possessing a two-guest binding ability. [Zn(L1)(OAc)2] affords the 1:2 complex [Zn(L1)(G1)2] (G = guest molecule) with 4-nitrobenzoate ion (G1). The X-ray crystal structure of [Zn(L1)(G1)2] confirms that Zn(L1)2+ accommodates two 4-nitrobenzoate moieties and that the coordination geometry around ZnII is a distorted square pyramid. Two independent molecules are present in the asymmetric unit to form the π-stacked dimer by face-to-face overlap. Fluorescence quenching of [Zn(L1)(G1)2] is observed by intramolecular electron transfer from the pyrenyl moieties to the ZnII-bound 4-nitrobenzoates.