Finished Research Topics

Chalkogenido metallates are attractive building blocks for the rational synthesis of inorganic frameworks by solution reactions. An important model is the rich structural chemistry of silicates, which derives from differently connected SiO₄ tetrahedra.

Thiosilicate in solution

The solution chemistry of the simplest variation of silicates, in which oxygen is replaced by sulfur, known as thiosilicates from solid state compounds, was completely missing . Through solvatation of SiS₂ in liquid ammonia  we found (NH₄)₂[SiS₃(NH₃)]·2NH₃ as the first soluble orthothiosilicate (SiS₄⁴⁻) derivative.

Chalcogenidoplumbates

Germanates or stannates are known to be soluble in .... In contrast, thio, selenido and tellurido plumbates cannot behandled in these solvents. In liquid ammonia it was possible for the first time to gain both the highly charged original ion PbSe₃⁴⁻ and the dimeric compound Pb₂Se₄⁴⁻.

fig. 1: The monomeric selenido plumbate PbSe₃⁴⁻ as it can be found e. g. in the ammoniate Rb₄PbSe₃·2NH₃ (left). The dimeric anions Pb₂Se₄⁴⁻ in cis (mid) or trans conformation (right) which exist in the compounds[Li(NH₃)₄]₂Li₂Pb₂Se₄·5NH₃ or [Li(NH₃)₄]₂Li₂Pb₂Se₄·4NH₃.

In contrast to O−H⋯O hydrogen bonds in solvate crystals containing water, which are called hydrates, the analogous N−H⋯N hydrogen bondings in ammoniates have hardly been explored. Through preparation of ammonia-rich crystals these structeres can be classified systematically and compared with hydrates with regard to differences and similarities.

Protonated and deprotonated ammonia clusters - acids and bases in NH₃

The strongest N−H⋯N hydrogen bonds can be observed in interactions to charged species. Both the ammonium ion NH₄⁺ as acid in the ammonia system, and amide NH₂⁻ as the base in the ammonia system form ammonia rich salts. During our invertigations the structure of protonated ammonia clusters like [NH₄(NH₃)₄]⁺, [(NH₄)₂(NH₃)₁₀]²⁺, ∞¹[NH₄(NH₃)₄(µ-NH₃)₂]⁺ (fig.1) and ∞¹[{N₂₆H₈₀}(µ-NH₃)₂]²⁺could be characterised for the first time. Dissolving alkaline metal amides in ammonia leads to recrystallization of ammonia rich compounds like KNH₂·2NH₃ and RbNH₂·2/3NH₃.

fig. 1: one dimensional complex strand of ∞¹[NH₄(NH₃)₄(µ-NH₃)₂]⁺ (the coordination environment of the ammonium ions is highlighted as blue tetrahedra)

Ammoniates in sugars and carboxylic acids

The interactaions of organic species like carboxylic acids, polyoles and carbohydrates with liquid ammonia have also hardly been explored. Potentially ammonia is an interesting alternative to polar solvents containing oxygen. The focus of this topic were solvability studies, structural chemistry of crystallizing ammoniates (fig. 2) and simple reactions with carbohydrates.

fig. 2: hydrogen bonds surrounding a polyole molecule in sorbitole pentaammoniate (left). Crystal structure of ammonium capronate monoammoniate, NH₄(C₅H₁₁COO)·NH₃ (right)