Aerogel-Based Single-Ion Magnets: A Case Study of a Cobalt(II) Complex Immobilized in Silica

• Published in: Molecules (Basel, Switzerland) Vol. 28; no. 1; p. 418
• Main Authors: Kottsov, Sergey Yu, Shmelev, Maxim A, Baranchikov, Alexander E, Kiskin, Mikhail A, Sharipov, Alim U, Efimov, Nikolay N, Rubtsova, Irina K, Nikolaevskii, Stanislav A, Kopitsa, Gennady P, Khamova, Tamara V, Roslyakov, Ilya V, Eremenko, Igor L, Ivanov, Vladimir K
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 01.01.2023; MDPI
• Subjects: aerogel; Bulk density; Carbon dioxide; Case studies; chemical immobilization; Cobalt; Cobalt - chemistry; Cobalt compounds; Diamines; Ethylenediamine; Ethylenediamines; Immobilization; Information storage; Ions; Magnetic induction; Magnetic measurement; magnetic properties; Magnetic relaxation; Magnetics; Magnetization; Magnetization reversal; Magnets; N-3-(trimethoxysilyl)propyl ethylenediamine; Nanoparticles; Porosity; Silica; Silica aerogels; Silicon dioxide; Silicon Dioxide - chemistry; single-ion magnet; single-molecule magnet; United Kingdom; United States; Germany; Russia; magnetic properties; electron paramagnetic resonance; single-ion magnet; chemical immobilization; single-molecule magnet; Raman spectroscopy; aerogel; N-3-(trimethoxysilyl)propyl ethylenediamine
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules28010418

The chemical immobilization of cobalt(II) ions in a silica aerogel matrix enabled the synthesis of the first representative example of aerogel-based single-ion magnets. For the synthesis of the lyogels, methyl-trimethoxysilane and N-3-(trimethoxysilyl)propyl ethylenediamine were co-hydrolyzed, then the ethylenediamine groups that were immobilized on the silica matrix enabled the subsequent binding of cobalt(II) ions. Lyogels with various amounts of ethylenediamine moieties (0.1-15 mol %) were soaked in isopropanol solutions of cobalt(II) nitrate and further supercritically dried in carbon dioxide to obtain aerogels with a specific surface area of 210-596 m ·g , an apparent density of 0.403-0.740 cm ·g and a porosity of 60-78%. The actual cobalt content in the aerogels was 0.01-1.50 mmol per 1 g of SiO , which could easily be tuned by the concentration of ethylenediamine moieties in the silica matrix. The introduction of cobalt(II) ions into the ethylenediamine-modified silica aerogel promoted the stability of the diamine moieties at the supercritical drying stage. The molecular prototype of the immobilized cobalt(II) complex, bearing one ethylenediamine ligand [Co(en)(MeCN)(NO ) ], was synthesized and structurally characterized. Using magnetometry in the DC mode, it was shown that cobalt(II)-modified silica aerogels exhibited slow magnetic relaxation in a nonzero field. A decrease in cobalt(II) concentration in aerogels from 1.5 mmol to 0.14 mmol per 1 g of SiO resulted in a weakening of inter-ion interactions; the magnetization reversal energy barrier likewise increased from 4 to 18 K.