Formation,Expansion, and Interconversion of Metallarings in a Sulfur‐Bridged AuICoIII Coordination System

A novel Au^ICo^III coordination system that is derived from the newly prepared [Co(D ‐nmp)₂]⁻ ( 1 ⁻; D ‐nmp=N‐methyl‐D ‐penicillaminate) and a gold(I) precursor Au^I is reported. Complex 1 ⁻ acts as a sulfur‐donating metallaligand and reacts with the gold(I) precursor to give [Au₂Co₂(D ‐nmp)₄] ( 2 ), which has an eight‐membered Au^I₂Co^III₂ metallaring. Treatment of 2 with [Au₂(dppe)₂]²⁺ (dppe=1,2‐bis(diphenylphosphino)ethane) leads to the formation of [Au₄Co₂(dppe)₂(D ‐nmp)₄]²⁺ ( 3 ²⁺), which consists of an 18‐membered Au^I₄Co^III₂ metallaring that accommodates a tetrahedral anion (BF₄⁻, ClO₄⁻, ReO₄⁻). In solution, the metallaring structure of 3 ²⁺ is readily interconvertible with the nine‐membered Au^I₂Co^III metallaring structure of [Au₂Co(dppe)(D ‐nmp)₂]⁺ ( 4 ⁺); this process depends on external factors, such as solvent, concentration, and nature of the counteranion. These results reveal the lability of the Au S and Au P bonds, which is essential for metallaring expansion and contraction.     

Controlling Lanthanide Exchange in Triple‐Stranded Helicates: A Way to Optimize Molecular Light‐Upconversion

The kinetic lability of hexadentate gallium‐based tripods is sufficient to ensure thermodynamic self‐assembly of luminescent heterodimetallic [GaLn( L3 )₃]⁶⁺ helicates on the hour time scale, where Ln is a trivalent 4f‐block cation. The inertness is, however, large enough for preserving the triple‐helical structure when [GaLn( L3 )₃]⁶⁺ is exposed to lanthanide exchange. The connection of a second gallium‐based tripod further slows down the exchange processes to such an extent that spectroscopically active [CrErCr( L4 )₃]⁹⁺ can be diluted into closed‐shell [GaYGa( L4 )₃]⁹⁺ matrices without metal scrambling. This feature is exploited for pushing molecular‐based energy‐transfer upconversion (ETU) at room temperature.