Zn(NH3)2Cl2, a Mineral-like Anthropogenic Phase with Ammine Complexes from the Burned Dumps of the Chelyabinsk Coal Basin, South Urals, Russia: Crystal Structure, Spectroscopy and Thermal Evolution

Abstract

The mineral-like anthropogenic phase Zn(NH3)2Cl2, with ammine (NH30) complexes from the burned dumps of the Chelyabinsk coal basin (South Urals, Russia), has been investigated using single-crystal and high-temperature powder X-ray diffraction, and Raman and infrared (IR) spectroscopy. The anthropogenic Zn(NH3)2Cl2 is orthorhombic, Imma, a = 7.7399(6), b = 8.0551(5), c = 8.4767(8) Å, V = 528.49(7) Å3, R1 = 0.0388 at −73 °C. Its crystal structure is based upon isolated ZnN2Cl2 tetrahedra connected by hydrogen bonds (between NH3 groups and Cl atoms) into a three-dimensional network. Upon heating, the Zn(NH3)2Cl2 phase is stable up to about 150 °C, which is in good agreement with the data on the temperature of its formation. The crystal structure of Zn(NH3)Cl2 expands anisotropically with the strongest thermal expansion observed along the a axis. The thermal expansion of the structure is controlled by the changes in the hydrogen bonding system. The Raman and IR spectroscopic characteristics of this phase are close to those of the mineral ammineite, CuCl2(NH3)2. The studied anthropogenic phase, formed in the unique conditions of burned coal dumps, is identical to the synthetic Zn(NH3)2Cl2.