Hexanuclear iron( iii ) α-aminophosphonate: synthesis, structure, and magnetic properties of a molecular wheel

• Published in: New journal of chemistry Vol. 42; no. 3; pp. 1931 - 1938
• Main Authors: Doroshenko, Iaroslav, Babiak, Michal, Buchholz, Axel, Tucek, Jiri, Plass, Winfried, Pinkas, Jiri
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2018
• Subjects: Ammonia; Antiferromagnetism; Cations; Chemical synthesis; Coupling (molecular); Crystal structure; Infrared radiation; Iron; Iron 57; Ligands; Magnetic measurement; Magnetic properties; Magnetism; Molecular structure; Mossbauer spectroscopy; Protonation; Single crystals; Spectrum analysis
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/C7NJ03606J

A new hexanuclear molecular iron phosphonate complex, [Fe 6 (HAIPA) 12 (OH) 6 ]· n H 2 O ( 1 · n H 2 O) (H 2 AIPA = NH 2 (CH 3 ) 2 CP(O)(OH) 2 , (2-aminopropan-2-yl)phosphonic acid), was synthesized from Fe 2+ and Fe 3+ salts in water by interaction with the ligand salts. Addition of corresponding amounts of sodium or tetramethylammonium salts of H 2 AIPA to the solution of iron precursors led to the formation of large bright-green crystals of complex 1 . Isolated products were studied by spectroscopic and analytical methods – IR, Mössbauer spectroscopy, TG/DSC, ICP-OES, and CHN analysis. A novel {Fe 6 } hexanuclear molecular structure of 1 was confirmed by single crystal X-ray diffraction analysis. An octahedral coordination environment of iron cations is formed by phosphonate and hydroxo oxygens. Twelve phosphonate groups and six –OH groups act as bridging ligands and bind six Fe octahedra. Because of protonation of the amino group, the phosphonate anions coordinate in the zwitterionic form as HAIPA − (NH 3 + (CH 3 ) 2 CPO 3 2− ). The iron cations are present in the form of high-spin Fe 3+ , which was confirmed by the bond valence sum (BVS) calculations and the 57 Fe Mössbauer spectra. The magnetic measurements show antiferromagnetic coupling between the iron centers with decreasing temperature.