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北京石油化工學(xué)院2026年研究生招生接收調(diào)劑公告

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donglijie

銀蟲 (初入文壇)

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[求助] Conventional and Unconventional MetalOrganic Frameworks Based

The class of materials known as metalorganic frameworks,
or MOFs, is the subject of an enormous amount of current
research. The other reviews in this issue serve as testament to this
fact. The defining character of these compounds is their porosity,
which can be tuned by changing the geometry and size of the
carboxylic acid ligands. In the early years of this research,
carboxylate-based MOFs were designed to have ever-greater
surface areas, resulting in the astonishing increase from 600
to >5000 m2/g.16 In addition, interest was keyed toward very
large uptake of certain gases such as hydrogen, methane, and
carbon dioxide and the possibility of a range of potential gas
separations. The number of reported MOFs has skyrocketed as
researchers have explored the vast number of possible combinations
of ligand design, transition metals, coligands, and structuredirecting
agents. Many investigators were fascinated by the idea
that one could use a set of principles to define structures that
would be porous. However, although many papers claim to have
created porous products, the structural data is insufficient. One
must have a sorption isotherm to prove the extent of porosity.
Carboxylate-based MOFs have been shown to have remarkably
high surface area and uniform pore size distribution, but
their lack of stability in air and water poses a significant problem if
they are to be used in industrial or commercial applications.
Divalent metal carboxylates are subject to hydrolysis and usuallyquite soluble in acid solution. It should be pointed out that other
types of MOFs, such as those based on pyrazolate ligands, can be
much more robust.7 Phosphonates form stronger bonds than
carboxylates do with metal atoms, so it is natural that investigators
should try to prepare phosphonate-based MOFs. From our
own experience, monovalent metal phosphonates are highly
soluble, even though they may crystallize as supramolecular
structures. As the valence of the metal increases, the solubility
decreases. Divalent metal phosphonates are soluble enough that
single crystals can be obtained by hydrothermal or solvothermal
techniques, whereas trivalent and tetravalent metal phosphonates
are rarely crystalline as they are highly insoluble and tend
to precipitate as poorly ordered layered materials. The tetravalent
metal phosphonates are insoluble even in strong acid solution.
Phosphonates have three oxygen atoms capable of bonding
to metals. They can also coordinate metals when they are in any
state of protonation. This results in many possible modes of cocoordination
and myriad different arrangements that the structures
can take, many of which are not porous and therefore not MOFs.
The majority of metal phosphonate compounds are not MOFs,
and although there are a number of instances where phosphonate-
based MOFs have been prepared, they were generally not
by design. The interested reader is directed to a recently released
book for more information.

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hookhans

鐵桿木蟲 (著名寫手)

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★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ...
phu_grassman: 金幣+5, thanks 2013-03-11 16:23:05
donglijie: 金幣+100, 翻譯EPI+1, ★★★★★最佳答案 2013-03-11 16:46:15

金屬有機骨架化合物，即MOFs，是目前投入大量研究的一類材料。在這方面的（大量)其它綜述可以作為這一結(jié)論的佐證。這些化合物的確定特征是它們具有的孔性，可以通過改羧酸基配體的幾何結(jié)構(gòu)和尺寸來調(diào)變。在早些年的研究中，羧基的MOFs研究主要朝向設(shè)計前所沒有的表面積，結(jié)果其表面積得到驚人的提高，從600 to >5000 m2/g. 此外，研究興趣還集中在其大量吸收一些氣體上，比如，氫氣、甲烷、二氧化碳，以及其用于氣體分離的潛在可能性。隨著研究人員發(fā)掘出大量配體設(shè)計、過度金屬、共配體、結(jié)構(gòu)導(dǎo)向劑之間的可行性組合方法，有關(guān)MFOs的報道數(shù)量急劇飆升。很多研究者滿足于能夠用一系列的既定方法來確定結(jié)構(gòu)的孔道性。然而，盡管很多文章聲明他們構(gòu)建了孔性材料，但是結(jié)構(gòu)方面的數(shù)據(jù)還是欠缺。孔性必須用吸附曲線來證明。羧酸基的MOFs 已經(jīng)顯示其具有驚人的高表面積和均一的孔尺寸分布，但是由于它們在空氣或水中缺乏穩(wěn)定性，因此在工業(yè)或商業(yè)化應(yīng)用中遇到很大的問題。二價金屬的羧酸通常在酸性溶液中水解，并且很穩(wěn)定。應(yīng)該指出的是，其它類型的 MOFs, 比如那些基于吡唑特基配體的MOFs, 可以更穩(wěn)定存在。因為磷酸基比羧酸基能與金屬成更強的鍵，因此研究者們嘗試制備磷酸基的MOFs是自然而然的事情。從我們的實驗來看，單價的金屬磷酸具有高溶解性，盡管它們會以超分子結(jié)構(gòu)的形式結(jié)晶。隨著金屬價態(tài)的增加，溶解性降低。二價金屬磷酸具有足夠的溶解性，能夠通過水熱或溶劑熱的技術(shù)得到單晶；而三價和四價的金屬磷酸很少結(jié)晶，因為它們?nèi)芙庑院懿�，通常趨向于形成無序的層狀結(jié)構(gòu)材料。三價和四價的金屬磷酸甚至不溶于強酸。磷酸具有三個可以和金屬成鍵的氧原子，它們甚至在任何質(zhì)子化狀態(tài)下仍能和金屬配位。這就導(dǎo)致材料結(jié)構(gòu)可以采取很多的可能配位模型和大量的不同的組合，而其中的很多結(jié)構(gòu)不是孔性的，因此不是MOFs。大多數(shù)金屬磷酸化合物不適MOFs，盡管有一些例子報道說制備了磷酸基的MOFs，但是它們都不是通過設(shè)計獲得的。更多信息，感興趣的讀者可以參考最近發(fā)布的一本書。

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