The preparation of
stable hypervalent metal complexes containing
Ag(III) has historically been challenging due to their propensity
for reduction under ambient conditions. This work explores the preparation
of a tripotassium silver bisperiodate complex as a tetrahydrate via
chemical oxidation of the central silver atom and orthoperiodate chelation.
The isolation of the chelate complex in high yield and purity was
achieved via acidimetric titration. The comprehensive physiochemical
characterization of the tribasic silver bisperiodate included single
crystal X-ray diffraction, thermogravimetric and differential scanning
calorimetry, and infrared and ultraviolet–visible spectroscopy.
Infrared and UV–visible absorption spectra (λmax 255 and 365 nm) were in good agreement with historically prepared
pentabasic diperiodatoargentate chelate complexes. The C2/c monoclinic distorted square planar structure
of the bis-chelate complex affords a mutually supportive framework
to both Ag(III) and I(VII), conferring stability under both thermal
and long-term ambient conditions. Thermal analysis of the tribasic
silver bisperiodate complex identified an endothermic mass loss, ΔH = +278.35 kJ/mol, observed at 139.0 °C corresponding
to a solid-state reduction of silver from Ag(III) to Ag(I). Under
ambient conditions, no significant degradation was observed over a
12 month period (P = 0.30) for the silver bisperiodate
complex in a solid state, with an observed half-life of τ1/2 = 147 days in a pH-neutral aqueous solution.
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