A complex family of [Agpy_n]XO₄ (n=2-4, X=Cl, Mn, Re) with broad structural diversity was synthesized, and the crystal structures were solved with single-crystal X-ray diffraction. IR and Raman spectra were elucidated, moreover the thermal decomposition of the compounds was followed with TG-MS method.

The newly discovered perrhenate complex with n=3 has unique structure. The crystal lattice consists of isolated tripyridinesilver(I) cations, and five crystallographically different perrhenate anions: one perrhenate ion is tridentately coordinate to three silver ions, two perrhenate ions are coordinated monodentately to one silver ion each and there are two other perrhenates that do not coordinate to any silver. Weak hydrogen bonds are formed between the oxygens of the perrhenate anions and the pyridine ligands. No perchlorate and permanganate analogues could be synthesized with n=3, however [Agpy₂]XO₄.0.5py (X=Mn,Cl) and 4[Agpy₂][Agpy₄](XO₄)₅ (X=Cl, Mn) complexes were synthetized, whereas perrhenate analogues with n=2.5 and 2.4 did not form under analogue reaction conditions. For the complexes with X=Re, when n=2 or 4, the structure and spectroscopic studies were already discussed at the ACS Fall 2022, however, the TG-MS studies, thermal decomposition roots and the catalytic activity test of the formed Ag-Re-O phases were not discussed.

In this work, we discuss the results about the thermal decomposition of two perrhenate complexes with n=2 and 4. Both perrhenate complexes decompose below 100 °C (first decomposition steps) due to the quasi-solid phase redox reaction provided by the hydrogen bond network formed between the oxygens of the (oxidising) perrhenate anions and the ortho-hydrogens of the (reducing) pyridine ligands. These reactions ensure a convenient way to prepare oxide phases with nanometer-sized particles that are excellent catalysts candidates in various industrial processes, like the Fischer-Tropsch synthesis.

The unique structure of the newly discovered pyridinesilver(I) perrhenate complex with n=3.

Zoltán Homonnay

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