Unusual crystallographic existence of a hydrated zinc(ii) bisulphate complex: experimental and theoretical observations

Abstract

A unprecedented hydrated zinc(II) bisulphate complex, [Zn(H₂O)₆](HSO₄·H₂O)₂ (1) has been synthesized along with a molecular ion salt, [4,4′-bipy-H⁺][NCS⁻] (2) (4,4′-bipy = 4,4′-bipyridine) and characterized by different spectroscopic tools including a single crystal X-ray diffraction study. From the X-ray crystal structure of 1, it is revealed that the Zn(II) ion is in a perfect octahedral geometry with a ZnO₆ core and the molecule crystallizes in the P2₁/c space group. Self-assembly of the bisulphate anions with lattice water molecules pack to form a 12-membered cyclic cluster through strong intermolecular H-bonding (O–H⋯O–S). Again four cyclic tetramers interact with one another via H⋯O bonding to form a 20-membered macrocyclic bisulphate–water cluster and extends as a 2D network along the a axis. It presents a new mode of association of water molecules with bisulphate molecules. Density Function Theory (DFT) studies agree well with the experimental findings.