将钴(II)离子化学固定在二氧化硅气凝胶基质中,可以合成基于气凝胶的单离子磁体的第一个代表性示例。为了合成液凝胶,甲基三甲氧基硅烷和N-3-(三甲氧基甲硅烷基)丙基乙二胺共水解,然后固定在二氧化硅基质上的乙二胺基团使随后的钴(II)离子结合成为可能。将具有各种量的乙二胺部分(0.1-15mol%)的液凝胶浸入硝酸钴(II)的异丙醇溶液中,然后在二氧化碳中进一步超临界干燥,以获得比表面积为210-596m2·g-1的气凝胶,表观密度为0.403-0.740cm3·g-1,孔隙率为60-78%。气凝胶中的实际钴含量为0.01-1.50mmol/1克SiO2,这可以通过二氧化硅基质中乙二胺部分的浓度容易地调节。将钴(II)离子引入乙二胺改性的二氧化硅气凝胶中可促进二胺部分在超临界干燥阶段的稳定性。固定化钴(Ⅱ)配合物的分子原型,带有一个乙二胺配体[Co(en)(MeCN)(NO3)2],合成和结构表征。在直流模式下使用磁力测量,结果表明,钴(II)改性的二氧化硅气凝胶在非零场中表现出缓慢的磁弛豫。
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 m2·g-1, an apparent density of 0.403-0.740 cm3·g-1 and a porosity of 60-78%. The actual cobalt content in the aerogels was 0.01-1.50 mmol per 1 g of SiO2, 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)(NO3)2], 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 SiO2 resulted in a weakening of inter-ion interactions; the magnetization reversal energy barrier likewise increased from 4 to 18 K.