Isolation and characterization of ZnII and HgII coordination polymers with a designed azo-aromatic ligand: Identification of micrometer- and nanometer-sized particles

Abstract

Controlled layering of the deprotonated methanolic solution of the azo-aromatic ligand [L3]- (HL3 = 2-[3-(pyridylamino)-phenylazo]pyridine) over the aqueous/methanolic solutions of metal chlorides MCl2 (M = Zn, Hg) afforded nano- and micrometer-sized particles of the metal-organic polymeric complexes of [HgCl(C16H12N5)]∞ (1) and [ZnCl-(C16H18N5O3)] ∞ (2). Time-dependent growth of the above particles is followed by the SEM and TEM analyses of the samples at different time intervals. The X-ray structure of the mercury polymer reveals that two infinite 1D, zigzag chains composed of [HgCl(L3)]∞ units run along the a axis antiparalelly. The polynuclear Zn compound, in contrast, agglomerates fast to form hemispherical microcrystals with a diamondoid surface morphology, and no suitable X-ray quality crystal of this complex could be isolated. Powder XRD analyses of the samples as well as thermogravimetric analysis (TGA) are used for their characterization. Unusually, these metal-organic polymers of the reference d10 metal ions are green and absorb in the low-energy region of the visible spectrum, 660-675 nm. Semiempirical calculations on a representative complex 1 suggest that the transitions in the complexes involve ligand orbitals. These also show multiple emissions in the blue-green region. The Zn complex, which is microporous, shows reversible adsorption/desorption of N2 and H2 gasses. The mercury polymer, on the other hand, shows poor adsorption ability. © Wiley-VCH Verlag GmbH & Co. KGaA, 2007.