School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
Inorg Chem. 2011 Oct 3;50(19):9374-84. doi: 10.1021/ic200967b. Epub 2011 Sep 7.
Three isostructural anionic frameworks {[(Hdma)(H(3)O)][In(2)(L(1))(2)]·4DMF·5H(2)O}(∞) (NOTT-206-solv), {[H(2)ppz][In(2)(L(2))(2)]·3.5DMF·5H(2)O}(∞) (NOTT-200-solv), and {[H(2)ppz][In(2)(L(3))(2)]·4DMF·5.5H(2)O}(∞) (NOTT-208-solv) (dma = dimethylamine; ppz = piperazine) each featuring organic countercations that selectively block the channels and act as pore gates have been prepared. The organic cations within the as-synthesized frameworks can be replaced by Li(+) ions to yield the corresponding Li(+)-containing frameworks {Li(1.2)(H(3)O)(0.8)[In(2)(L(1))(2)]·14H(2)O}(∞) (NOTT-207-solv), {Li(1.5)(H(3)O)(0.5)[In(2)(L(2))(2)]·11H(2)O}(∞) (NOTT-201-solv), and {Li(1.4)(H(3)O)(0.6)[In(2)(L(3))(2)]·4acetone·11H(2)O}(∞) (NOTT-209-solv) in which the pores are now unblocked. The desolvated framework materials NOTT-200a, NOTT-206a, and NOTT-208a display nonporous, hysteretic and reversible N(2) uptakes, respectively, while NOTT-206a and NOTT-200a provide a strong kinetic trap showing adsorption/desorption hysteresis with H(2). Single crystal X-ray analysis confirms that the Li(+) ions are either tetrahedrally (in NOTT-201-solv and NOTT-209-solv) or octahedrally (in NOTT-207-solv) coordinated by carboxylate oxygen atoms and/or water molecules. This is supported by (7)Li solid-state NMR spectroscopy. NOTT-209a, compared with NOTT-208a, shows a 31% enhancement in H(2) storage capacity coupled to a 38% increase in the isosteric heat of adsorption to 12 kJ/mol at zero coverage. Thus, by modulating the pore environment via postsynthetic cation exchange, the gas adsorption properties of the resultant MOF can be fine-tuned. This affords a methodology for the development of high capacity storage materials that may operate at more ambient temperatures.
三种等结构的阴离子骨架{(Hdma)(H(3)O))[In(2)(L(1))(2)]·4DMF·5H(2)O}(∞) (NOTT-206-solv)、{[H(2)ppz][In(2)(L(2))(2)]·3.5DMF·5H(2)O}(∞) (NOTT-200-solv) 和 {[H(2)ppz][In(2)(L(3))(2)]·4DMF·5.5H(2)O}(∞) (NOTT-208-solv)（dma = 二甲胺；ppz = 哌嗪），每个骨架都具有选择性地阻塞通道并充当孔门的有机抗衡阳离子。合成框架内的有机阳离子可以被 Li(+)离子取代，得到相应的含有 Li(+)的框架{(Li(1.2)(H(3)O)(0.8)[In(2)(L(1))(2)]·14H(2)O}(∞) (NOTT-207-solv)、{(Li(1.5)(H(3)O)(0.5)[In(2)(L(2))(2)]·11H(2)O}(∞) (NOTT-201-solv) 和 {(Li(1.4)(H(3)O)(0.6)[In(2)(L(3))(2)]·4acetone·11H(2)O}(∞) (NOTT-209-solv)，其中孔现在未被阻塞。脱溶剂骨架材料 NOTT-200a、NOTT-206a 和 NOTT-208a 分别显示出无孔、滞后和可逆的 N(2)吸光度，而 NOTT-206a 和 NOTT-200a 提供了一个强动力学陷阱，显示出与 H(2)的吸附/解吸滞后。单晶 X 射线分析证实，Li(+)离子要么是四面体形（在 NOTT-201-solv 和 NOTT-209-solv 中），要么是八面体形（在 NOTT-207-solv 中），由羧酸盐氧原子和/或水分子配位。这得到了 (7)Li 固态 NMR 光谱的支持。与 NOTT-208a 相比，NOTT-209a 在零覆盖率下的氢气存储容量提高了 31%，同时吸附等焓增加了 38%，达到 12 kJ/mol。因此，通过后合成阳离子交换调节孔环境，可以微调所得 MOF 的气体吸附性能。这为开发可能在更环境温度下运行的高容量存储材料提供了一种方法。
