Synthesis of the water dispersible L-valine capped ZnS:Mn nanocrystal and the crystal structure of the precursor complex: [Zn(Val)2(H 2O)]

Abstract

The L-Valinate anion coordinating zinc complex, [Zn(val)2(H 2O)], was isolated and structurally characterized by single crystal X-ray crystallography. The crystal possess orthorhombic symmetry with a space group P212121, Z = 4, and a = 7.4279(2) Å, b = 9.4342(2) Å, c =20.5862(7) Å respectively. The compound features a penta-coordinate zinc ion in which the two valine anion molecules are directly coordinating the central zinc metal ion via their N (amine) and O (carboxylate) atoms, and an additional coordination to zinc is made by water molecule (solvent) to form a distorted square pyramidal structure. In addition, further synthesis of the valine capped ZnS:Mn nanocrystal from the reaction of [Zn(val)2(H2O)] precursor with Na2S and 1.95 weight % of Mn2+ dopant is described. Obtained valine capped nanocrystal was water dispersible and was optically characterized by UV-vis and solution PL spectroscopy. The solution PL spectrum for the valine capped ZnS:Mn nanocrystal showed an excitation peak at 280 nm and a very narrow emission peak at 558 nm respectively. The measured and calculated PL efficiency of the nanocrystal in water was 15.8%. The obtained powders were characterized by XRD, HR-TEM, and EDXS analyses. The particle size of the nanocrystal was also measured via a TEM image. The measured average particle size was 3.3 nm.