‘Rings and rectangles’ mediated through weak interactions in ionic solids: Synthesis and packing analysis of [Co(NH3)6]Cl2SeCN and [Co(NH3)6]3Cl4(N3)5 in the crystalline state

Abstract

The reaction of hexaamminecobalt(III) chloride with sodium azide and potassium selenocyanate (1 ∶ 3 molar ratio) in hot aqueous medium leads to formation of reddish-orange crystals of composition [Co(NH₃)₆]Cl₂SeCN (1) and [Co(NH₃)₆]₃Cl₄(N₃)₅ (2), respectively. Single crystal X-ray structural analysis of 1 and 2 reveals the supramolecular hydrogen bonding network between ionic groups (i.e. SeCN⁻ or N₃⁻ and Cl⁻) and the hydrogen atom of the coordinated NH₃ molecules leading to the formation of ‘rings’ (in 1) or ‘rectangles’ (in 2) of ions in their respective lattices. Though linear, small topological difference of size and shape between the selenocyanate and azide anions manifests in different packing modes in these compounds. The formation of a ‘small’ rectangle inside a ‘large’ rectangle of ions makes the packing of 2 remarkably unique.