A Shape-Complementarity Approach to Inducing Short Au(III)···Au(III) Contacts in Tetracyanoaurate(III) Salts

Area of Science:

• Inorganic Chemistry
• Crystal Engineering
• Supramolecular Chemistry

Background:

• Tetracyanoaurate(III) anions ([Au(CN)4]-) are known to form noncovalent interactions.
• Aurophilicity, the attractive interaction between gold(I) or gold(III) centers, is a key factor in the assembly of gold complexes.
• Understanding the factors that control the self-assembly of anionic metal complexes is crucial for designing novel materials.

Purpose of the Study:

• To synthesize and structurally characterize novel tetracyanoaurate(III) salts with various metal-ligand complex cations.
• To investigate the influence of cation shape, size, and symmetry on the noncovalent assembly of [Au(CN)4]- anions.
• To explore the occurrence of Au(III)···Au(III) interactions (aurophilicity) and their relationship with crystal packing.

Main Methods:

• Synthesis and single-crystal X-ray diffraction of six sets of tetracyanoaurate(III) salts.
• Computational methods to study Au(III) aurophilicity.
• Hirshfeld surface analysis to probe crystal packing.
• Investigation of photoluminescence properties of selected compounds.

Main Results:

• Six novel tetracyanoaurate(III) salts were successfully synthesized and characterized.
• Cation geometry was found to be critical in directing the assembly of [Au(CN)4]- anions, enabling Au(III)···Au(III) contacts.
• Modification of cations led to isoreticular replacement of anionic trimers with unusual Au-Cl-Au bridged dimers, demonstrating adaptability in anionic group assembly.
• Compounds containing the [Eu(dmbipyO2)4]3+ luminophore exhibited high photoluminescence quantum yields (ca. 50%).

Conclusions:

• The shape and symmetry of metal-ligand complex cations play a decisive role in controlling the supramolecular assembly of tetracyanoaurate(III) anions.
• Specific cation packing can induce Au(III)···Au(III) aurophilic interactions, leading to the formation of aligned dimers or trimers.
• The study demonstrates the intricate interplay between cation structure, anion assembly, and the manifestation of aurophilicity in gold(III) complexes.
• The findings offer insights into the rational design of crystalline materials with tailored structural and photophysical properties.