Anion-dependent crystallization of zinc complexes with the ligand 4′,5′-diaza-9′-(4,5-disubstituted-1,3-dithiol-2-ylidene) fluorene: Structures and spectroscopic properties

Abstract

A series of zinc(II) complexes (1–6) with the ligands 4′,5′-diaza-9′-(4,5-bis(methylthio)-1,3-dithiol-2-ylidene) fluorene (L¹) or 4′,5′-diaza-9′-(4,5-bis(ethylthio)-1,3-dithiol-2-ylidene) fluorene (L²) have been prepared in the presence of different zinc(II) salts, [Zn(L¹)₂(NO₃)(MeOH)](NO₃)·CH₂Cl₂·0.5(MeOH)·0.5(EtOH) (1), [Zn(L¹)₂(PhCOO)]NO₃·MeOH (2) (PhCOO = benzoic ion), [Zn(L¹)₂Cl] [Zn(L¹)Cl₂] [ZnCl₃(MeOH)]·CH₂Cl₂·H₂O (3), [Zn(L¹)₂(ClO₄)₂] (4), [Zn(L²)₂Cl] [Zn(L²)Cl₂] [ZnCl₃(MeOH)]·0.5(MeOH) (5), and [Zn(L²)₂(ClO₄)₂] (6). Five of the complexes (1–3, 5, and 6) have been structurally characterized by single-crystal X-ray diffraction. The preferred coordination geometry of the zinc(II) center is related to the coordinated anions. Complexes 1, 2 and 6 with oxo-anions display distorted octahedral geometry, while complexes 3 and 5 with chloride anions take five- and four-coordination geometries. The weak coordinated perchlorate anion prefers a trans structure, while the strong coordinated nitrate anion favors a cis structure. The intermolecular C⋯C, C⋯S, and S⋯S interactions lead to the assembly of the complexes into different supramolecular frameworks. The results of the ¹H NMR, UV-vis, and fluorescent spectra display a large effect of metal coordination on the electron density of the ligand. Spectral data for the complexes is in agreement with the crystal structures. Finally, semi-empirical PM3 calculations were carried out to explain the relationship of the structures and the spectra.