Oxonium trans‐bis(oxalato)rhodate and related sodium salts: a rare example of crystalline complex acid

• Published in: Acta crystallographica Section B, Structural science, crystal engineering and materials Structural science, crystal engineering and materials, 2021-12, Vol.77 (6), p.1048-1054
• Main Authors: Garkul, Ilia, Zadesenets, Andrey, Filatov, Evgeny, Baidina, Iraida, Tkachev, Sergey, Samsonenko, Denis, Korenev, Sergey
• Format: Article
• Language: English
• Subjects: Acids; Chemical analysis; Coordination compounds; Crystals; Infrared analysis; Infrared spectroscopy; NMR analysis; NMR spectroscopy; oxalato complexes; Oxalic acid; Rhodium; Rhodium isotopes; single crystal X‐ray diffraction; Single crystals; Sodium; Sodium salts; Spectrum analysis
• ISSN: 2052-5206; 2052-5192; 2052-5206
• DOI: 10.1107/S205252062101115X

New coordination compounds trans‐bis(oxalato)diaquarhodiate sodium dihydrate Na[Rh(H2O)2Ox2]·2H2O (crystallizes in two polymorphic forms NaRh‐1 and NaRh‐2), trans‐bis(oxalato)hydroxoaquarhodiate sodium tetrahydrate Na2[Rh(H2O)(OH)Ox2]·4H2O (Na2Rh) and trans‐bis(oxalato)diaquarhodic acid tetrahydrate (H3O)[Rh(H2O)2Ox2]·4H2O (HRh) are synthesized. The compounds are characterized by IR spectroscopy, elemental analysis and single crystal X‐ray diffraction. NaRh‐1, NaRh‐2 and Na2Rh crystallize in space group P1. Trans‐bis(oxalato)diaquarhodic acid exists not only in solution, but can also crystallize as a tetrahydrate (space group C2/c). The formation of various species in solution of rhodium hydroxide in oxalic acid and their redistribution were studied using 103Rh NMR spectroscopy. The polymorphism of Na[Rh(H2O)2(C2O4)2]·2H2O is noteworthy. The complex crystallizes with the formation of two different structures of the same water content. Oxalato‐rhodic acid not only exists in solution, but, unlike most complex acids, it can also crystallize as a tetrahydrate.