Proton Magnetic Resonance Study of Crystalline Potassium Trisoxalatorhodium(III) Hydrate

Abstract

The broad‐line proton magnetic resonance spectrum of crystalline potassium trisoxalatorhodium(III) hydrate, K₃Rh(C₂O₄)₃4½H₂O, has been investigated in the temperature range 77°K—330°K. The spectrum at 77°K indicates that some of the protons in the crystal are not present in water of crystallization and an analysis of this same spectrum indicates that the compound should be formulated as $${\mathrm{K}}_6[\mathrm{Rh}({\mathrm{C}}_2{\mathrm{O}}_4{)}_3\mathrm{][}\mathrm{Rh}({\mathrm{C}}_2{\mathrm{O}}_4{)}_2({\mathrm{HC}}_2{\mathrm{O}}_4\mathrm{)(}\mathrm{OH}\text{)]8}{\mathrm{H}}_2\mathrm{O}.$$ This formula is not inconsistent with the chemical reactions that the compound undergoes, and it explains some properties which are not satisfactorily accounted for by the previously accepted formula $${\mathrm{K}}_3[\mathrm{Rh}({\mathrm{C}}_2{\mathrm{O}}_4{)}_3\text{]4}\frac{1}{2}{\mathrm{H}}_2\mathrm{O}.$$ The absorption spectrum at 318°K substantiates the analysis of the spectrum at 77°K and it also indicates that the water of crystallization can be grouped into at least three sets, the water molecules in different sets having different degrees of mobility. The proton magnetic resonance data also indicate that the ``monohydrate,'' K₃Rh(C₂O₄)₃H₂O, is probably ${\mathrm{K}}_6[\mathrm{Rh}({\mathrm{C}}_2{\mathrm{O}}_4{)}_3\mathrm{][}\mathrm{Rh}({\mathrm{C}}_2{\mathrm{O}}_4{)}_2({\mathrm{HC}}_2{\mathrm{O}}_4{)}_2(\mathrm{OH}\mathrm{)]}{\mathrm{H}}_2\mathrm{O}$ .