The discovery of the N,N-dimethylthioformamidium ion. A structural study of {(CH3)2NCHSH}2[HfCl6] in solid state and solution

Abstract

The crystal structure of N,N-dimethylthioformamidium hexachlorohafnate(IV), {(CH₃)₂NCHSH}₂[HfCl₆], obtained by dissolution of anhydrous hafnium(IV) chloride in N,N-dimethylthioformamide and storage under ambient atmosphere, has been determined from single crystal X-ray diffraction data. The bond distance distribution within the N,N-dimethylthioformamidium ion is similar to that in N,N-dimethylthioformamide molecules strongly bound to metal ions, but significantly different from that in pure N,N-dimethylthioformamide. The hafnium(IV) ion coordinates six chloride ions in a near-regular octahedral arrangement with a mean Hf–Cl bond distance of 2.447 Å. The packing in the crystal structure shows clearly the presence of hydrogen bonds of the X–(H)⋯Cl type, X = C and S, which are sufficiently strong and directional to hold the structure together. The structures of the hexachlorohafnate(IV), [HfCl₆]²⁻, and hexachlorozirconate(IV), [ZrCl₆]²⁻, ions in N,N-dimethylthioformamide solution have been determined by means of EXAFS, giving mean Hf–Cl and Zr–Cl bond distances of 2.44(1) and 2.45(1) Å, respectively. The infrared spectrum of solid {(CH₃)₂NCHSH}₂[HfCl₆] has been analysed and compared with the data for free and strongly coordinated N,N-dimethylthioformamide.