Chiral Porous Metal鈥揙rganic Frameworks of Co(II) and Ni(II): Synthesis, Structure, Magnetic Properties, and CO2 Uptake

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• 作者：C. M. Nagaraja ; Ritesh Haldar ; Tapas Kumar Maji ; C. N. R. Rao
• 刊名：Crystal Growth & Design
• 出版年：2012
• 出版时间：February 1, 2012
• 年：2012
• 卷：12
• 期：2
• 页码：975-981
• 全文大小：409K
• 年卷期：v.12,no.2(February 1, 2012)
• ISSN：1528-7505

文摘

Four isostructural chiral three-dimensional (3D) porous pillared-layer frameworks based on Co(II) and Ni(II), {[M(l-mal)(azpy)_0.5]路2H₂O}_n (M = Co (1), Ni (2)) and {[M(l-mal)(bpee)_0.5]路H₂O}_n(M = Co (3), Ni (4)); (l-mal = l-malate dianion, azpy = 4,4鈥?bisazobipyridine, and bpee = 1,2-bis(4-pyridyl)ethylene), have been synthesized using mixed ligand systems and characterized structurally. All the frameworks are homochiral, based on the chiral l-malate dianion. The bridging of l-malate with Co(II) or Ni(II) forms a two-dimensional (2D) layer of {M(l-mal)}_n which is further pillared by azpy or bpee to form a 3D pillared-layer porous framework. The large rectangular channels along the crystallographic b direction (7.0 脳 6.2 脜² for 1 and 2; 6.8 脳 6.1 脜² for 3 and 4) are occupied by the guest water molecules. The binding of 鈭扥H and 鈭扖OO groups of l-malate with the Co(II) or Ni(II) render interesting antiferromagnetic and ferrimagnetic type behavior in 1 and 2, respectively. All the frameworks show high thermal stability and guest-induced structural contraction evidenced by the temperature-dependent powder X-ray diffraction patterns. Gas (N₂, CO₂, H₂, O₂, and Ar) adsorption studies on the dehydrated frameworks of 1 and 3 show excellent selective CO₂ gas uptake at 195 K. The lesser uptake of CO₂ in the dehydrated framework of 3 compared to 1 has been rationalized to the different polarity of the pore surface due to the change in the functional group of the pillar module. The more polar azo (鈭扤鈺怤鈭? group in 1 renders strong interaction with CO₂ compared to the ethylenic (鈭扖H鈺怌H鈭? group in 3. The difference in polarity in 1 and 3 also is reflected in water sorption studies.