The seven stars of C&EN in 2019 have been announced, which ones have you guessed?
Last Update: 2020-06-19
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The slogan of the conference is "small atom with a big ego"An atom can change the worldThose who stand out in the dust and haze of the years are even more powerfulSome of them were thunderstruck at the beginning of their appearance, just like the treasure of heaven, which caused a great sensation in the academic circle; others were not in a hurry, just like a piece of gradually entering music, a telling story, waiting for the clouds to open and the moon to shine in their dormancy, waiting for the release of light and heat at that time< br / > every year, C & en magazine of ACS selects new molecules that have been published in major journals for one yearRecently, seven molecules have made the C & en's molecules of the year for 2019The academic Jingwei team is here to briefly introduce the unique structure and design concept of these seven molecules< br / > there is no biggest, only bigger: the re innovation record of all benzene substituted p-pbb < br / > the structure of all benzene substituted p-pbb has good semiconductor properties, and it is expected to be widely used in the field of organic optoelectronic materialsAs the name suggests, these molecules are composed of linear condensed benzene core skeleton, and then all condensed benzene C-H bonds are replaced by phenylIn 1996, Professor Robert APascal Jrof Tulane University completed the construction of octaphenylnaphthalene and decaphenylanthraceneAfter more than 20 years, they further expanded their molecular structure and synthesized dodecyl substituted tetrabenzenes< br / > picture source: reference  < br / > this molecule is the largest total benzene substituted polyphenyl structure that can be obtained by people at present, which is dark red and emits strong fluorescenceDue to the steric hindrance and electronic effect of the surrounding benzene substituents, the core skeleton of p-tetraphenylene is distorted to a certain extent, which is not a planar conjugate structure, and the torsion angle of the two ends connected end to end can reach 97 degreesAlthough the molecule is huge and complex, it can be synthesized effectively by three steps with tetraphenylfuran and 1,2,4,5-tetrabromo-3,6-diphenylbenzene as raw materials< br / > to fit methane into football, it's not difficult to sew the opening < br / > you may not be new to C60, which is one of the allotropes of carbon, with a hollow structure made up of 60 C atoms, and the shape is similar to football, so it's also called Football eneSince there is a hollow molecular cavity in C60, it is also assumed that other small molecules can be embedded into C60 with C60 as the molecular cageIn theory, it is very simple to realize this process: through specific chemical means, the C-C bonds of several consecutive 5 yuan carbon rings and 6 yuan carbon rings are cut off on one side of the football olefin, a gap is opened, then small molecules are introduced, and finally the rings are closed one by one by chemical means, and the spherical surface is "stitched"In the past, inorganic small molecules such as H2, H2O and HF have been embedded in C60If we want to "plug" larger molecules into the fullerene, we need to open a larger gap on its surfaceHowever, if the opening is too large, it will lead to the failure of further "stitching", thus limiting the size of the embedded molecules< br / > Professor Richard JWhitby's team at the University of Southampton, UK, opened a large gap on the side of C60 molecule, which is a 17 membered ring containing an S atom, and then "stuffed" CH4 into "football alkene under high pressureThe next step is the key "suture" step, in which the thioether in the gap is partially oxidized to sulfoxide, which is desulfonylated under the light initiation, and the first "closing" is completed, followed by the reduction of fullerene through the mature cyclization and aromatization processThis is the first time to embed organic molecules in C60, and the largest molecule so farCH4 can rotate freely in the molecular cage, and the carbon skeleton structure of fullerene has no obvious deformation< br / > picture source: reference  < br / > of course, this experiment is not just for fun, nor for OCDUsing this method, one can study the quantum properties of C in a single CH4 moleculeThe authors also plan to further embed other molecules such as O2 and NH3 into the fullerene< br / > can carbon also form hydrogen bonds? You heard me right < br / > Professor Amar hflood of Indiana University, US, designed a molecular cage that can capture chloride ions (Cl -) by using click reaction (Cu (I) - catalyzed cycloaddition reaction of terminal alkynes and azides)In the past, many groups of O-H and N-H bonds which can be used as hydrogen bond donor need to be modified in the structure of this kind of molecular cage That is to say, Cl - is introduced into the molecular cage through the strong hydrogen bond interaction between multiple groups of O-H and N-H bonds and Cl - < br / > picture source: reference  < br / > this work is realized through the interaction between the C-H bond of molecular cage and Cl - It seems that C-H bond can be used as hydrogen bond donor to overturn people's inherent impression of hydrogen bond Generally, only N, O, F atoms with large electronegativity and small atomic radius can form hydrogen bond interaction with H atoms The electronegativity difference between C and H is only 0.35, and the possibility of forming hydrogen bond is very small However, X-ray crystallography analysis has confirmed that there is a hydrogen bond interaction between C-H bond and Cl - in six groups of triazole structure in the molecular cage; in addition, the C-H bond in three groups of benzene ring also has a weak interaction with Cl -, resulting in the strong affinity of the molecular cage for Cl -, which is better than all other guest molecules at present, At the same time, it has good selectivity (Cl - > Br - > NO3 - > I -) < br / > if you ask how strong this affinity is, the author confessed that he spent nearly a year trying to isolate molecular cages that do not contain Cl -, but all ended in failure If the molecular cage is purified by column chromatography, the Cl - in silica gel will also be seized The minimum residue of Cl - can be controlled at about 10% Under normal conditions, Cl - can accelerate the corrosion of iron and steel materials, but the corrosion rate will be greatly reduced when the common steel is coated with a layer of molecular cage film < br / > the first case of all benzene ring mechanical interlocking structure, no heteroatoms, why not < br / > the work described below is quite topological art Professor Kenichiro Itami of Nagoya University in Japan and Professor yasutomo Segawa have designed two kinds of mechanical interlocking structures only composed of benzene ring, one is the double ring cable hydrocarbon formed by the interlocking of two linked cable rings, The other is a trefoil structure woven by a link < br / > picture source: reference  < br / > mechanical interlock structure is widely used in the field of molecular machinery It is not difficult to build two kinds of structures, namely, bicyclic hydrocarbon and trefoil linked cable ring The difficulty lies in the use of only benzene ring to design complex topological structure In general, to complete the above process, we need to use transition metal salt as template, coordinate it by heteroatoms (such as N, O) on the linked ring, or guide the construction of topological structure based on specific organic template molecules It is difficult to establish such a guiding function if the link is only composed of benzene ring < br / > the author thought of using spirodi (dibenzothiarole) as an organic template molecule to guide the synthesis of dicyclohydrocarbons and trefoil linked rings, adding fluoride to eliminate the central silicon atom, the two Phenyls of the original dibenzothiarole part will become a part of the linked ring, thus completing the construction of the mechanical interlock structure These two kinds of molecules are only composed of the repeat units of the para disubstituted benzene ring (C6H4) < br / > dormant for more than 50 years, the first all carbon ring came out < br / > in the early days, it was inferred that each C atom can bond with only two other C atoms to form a all carbon ring structure (ring [n] carbon, CN): each C atom and other C atoms form a C = C double bond, or form a C-C single bond and C ≡ C triple bond In 1966, it was proposed that cyclo  carbon (C18) may exist, but there has been a lack of effective methods to realize its synthesis and structural characterization After more than 50 years of rolling, Harry L Anderson, Professor Przemyslaw gawel of Oxford University and Dr Leo gross of IBM research-z ü rich, etc first used the atomic force microscope (AFM) to detect and image the c24o6 precursor and reaction intermediate of cyclic carbon oxide, and used the single atom manipulation technology to operate it at the atomic scale, The C = O group was cut off gradually by applying voltage pulse to the tip of the needle, and finally the synthesis of C18 was realized successfully < br / > Image Source: reference  < br / > this all carbon ring is completely composed of C atoms Under AFM imaging, there is a closed-loop structure with alternating C-C single bond and C ≡ C three bond This kind of structure can show good semiconductor properties, which means that C18 may play an important role in the field of nano electronic devices However, at present, they can only synthesize one molecule in a single operation To achieve large-scale synthesis of C18, and ensure that the molecule can remain stable after leaving the low temperature environment and inert matrix, there is still a long way to go < br / > it's not too late to wait for a hundred years: the coordination structure of the plane hexagon will eventually be dominant < br / > more than one hundred years ago, French chemist Alfred Werner put forward the "Werner coordination theory", which pioneered the coordination theory in inorganic chemistry For hexa coordinated transition metal complexes, in addition to the common octahedral and triangular coordination structures, he proposed that there should be another plane hexagon structure However, up to now, almost all six coordination transition metal complexes can not escape from the first two coordination configurations, and the third model has not been supported by examples < br / > however, after more than a century of ups and downs, this hypothesis was finally verified by the unremitting efforts of Professor Mark R crimmin of Imperial College London For the first time, they have successfully prepared and separated the complexes of palladium magnesium hydride, platinum magnesium hydride and nickel magnesium hydride with six coordination of planar hexagonal ligands The plane hexagonal coordination configuration was confirmed by X-ray diffraction analysis and DFT calculation < br / > Image Source: reference  < br / > is the anti aromaticity nano cage unstable? According to h ü ckel's rule, when the number of π electrons of a compound is 4N + 2, it shows aromaticity and chemical stability increases; when the number of π electrons is 4N, it shows anti aromaticity, chemical stability decreases and reaction activity increases The latter has paramagnetic ring current, which can play a unique role in magnetic materials With the rise of nanoscience research, various nanoscale structures have been designed, ranging from micro nano molecular cages to macro nano porous materials At present, nano molecular cage has been widely used in molecular recognition, separation and other aspects, and can also be used to promote some special chemical reactions The walls of most molecular cages are composed of aromatic molecules Because of the instability of anti aromatic molecules, there is no nano molecular cage composed of such molecules before < br / > professor Jonathan R Nitschke of Cambridge University, UK, designed a new kind of nano molecular cage for the first time with relatively stable anti aromatic molecules as cage walls The nonaromatic molecule is Ni (II) with demethylcarbrole coordination Norcorole is a kind of ring contraction porphyrin, in which two pyrrole rings are directly linked by C-C bond The π electron number of this kind of ring system is 16, so it shows anti aromaticity, but it is stable at room temperature and air atmosphere The nano molecular cages are tetrahedral in shape Six groups of Ni (II) with demethylcarbrole coordination are located in the edge line position, and four vertices are occupied by Fe2 + Demethylcarbrole side chains are modified with appropriate coordination groups to coordinate with them, so as to realize closed connection and form
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