Stabilization of gold-halogen heteropolycations with borosulfate anions

• Applicant: Dr. Jörn Bruns
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 528508733

The aim of the planned research project is to stabilize heteropolycations with borosulfate anions. The heteropolycations should always consist of gold and a halogen, whereby the oxidation state of the gold can vary from +1 to +3. The starting point of the experimental work is the synthesis of [Au3Cl4][B(S2O7)2] and [Au2Cl4][B(S2O7)2](SO3). By working under strongly oxidizing conditions in SO3, it has been possible to prepare the aforementioned compounds. These are stabilized by bis-disulfatoborate anions, which can be regarded as weakly coordinating anions. These anions are preferentially formed under these extreme conditions and will also serve for charge compensation of the cationic substructure for most of the compounds of the planned research project. In analogy to the synthesis of [Au3Cl4][B(S2O7)2] and [Au2Cl4][B(S2O7)2](SO3), further Au-Cl heteropolycations will be prepared from the reaction of boric acid with AuCl, AuCl2 and AuCl3 in SO3. Besides the variation of the stoichiometric composition, the influence of temperature on the product formation during the solvothermal reactions will be studied. Subsequently, gold bromides, iodides and fluorides will be used as starting materials. It is expected that the products of the reactions of AuBr and AuBr3 will form structures similar to those found for the chlorides. Since iodide anions are significantly larger and fluoride is significantly smaller, the products obtained should have different cationic substructures. For compounds containing Au2+, substitution with the isovalent cations Pd2+ or Hg2+ should be attempted. [Au2Cl4][B(S2O7)2](SO3) exhibits a wave-like arrangement of square planar coordinated Au2+ as well as Au3+ cations and has been characterized as a one-dimensional metal. Accordingly, after a routine characterization via single crystal and powder X-ray diffraction, IR and Raman spectroscopy as well as thermogravimetry, all obtained products of the research project will be subjected to further studies regarding magnetochemistry and conductivity, depending on the structure and nature of the products. Band structure calculations support the experimental results. For magentochemical measurements, conductivity measurements, XPS and band structure calculations, cooperation agreements have been made with colleagues at the University of Cologne.

• DFG Programme: Research Grants