Aromatic compounds: A ring made up solely of metal atoms
uni-heidelberg.de
uni-heidelberg.de
Aromatic metal compounds might be usable as highly efficient catalysts for organic reactions. These compounds could be used to create novel materials with interesting electronic, optical, or magnetic properties, so we could see better organic LEDs, better organic solar cells, conductive polymers, and improvements to magnetic materials for data storage. The unique structures of aromatic metal compounds could be exploited in drug design, potentially leading to new classes of therapeutic agents with improved efficacy or novel mechanisms of action. These compounds might be also used to create new types of nanostructures or improve existing ones, with potential applications in areas like sensing, drug delivery, or nanoelectronics. The electronic properties of aromatic metal compounds could potentially be harnessed to develop new types of batteries or supercapacitors with improved performance. The specific interactions between aromatic metal compounds and various analytes could be used to develop highly sensitive and selective chemical sensors. These compounds might exhibit interesting photochemical properties, leading to advancements in areas such as photocatalysis or light-harvesting materials for solar energy conversion.
We will know in ten years!
https://fastercapital.com/content/Electron-Mobility--Unleash...
This weirdness, that anything weird can happen at any time, leading to misery or a nature paper, is what makes chemistry so interesting and frustrating.
Relevant passage from the Nature article (https://www.nature.com/articles/s41557-024-01530-z)
During our investigation of 2 as a transmetallation agent, we observed an unusual reactivity with InBr3. The reaction of 2 with InBr3 in dichloromethane resulted in a rapid colour change from light orange to dark red. After standing for 3 days at room temperature, dark-coloured crystals of 3 developed (Fig. 3f). The synthesis is reproducible, yielding up to 28% of isolated 3. scXRD analysis showed a planar rhomboid {Bi4} ring encapsulated by two indiumbromide-calix[4]pyrrolates (...)Elemental bismuth is not a metal, but a semi-metal.
Solid metals have 2 characteristics that distinguish them from other kinds of substances. The first is the existence of free electrons, which makes them electrically conductive and optically reflective. The second is a crystal structure where each atom has many neighbors, whose consequence is that metals are ductile and malleable.
Already in the 18th century, semi-metals have been distinguished from metals. Semi-metals have only the first property. They have free electrons, but they have a crystal structure where each atom has only few neighbors, whose consequence is that semi-metals are fragile, even when pure (most metals can be made fragile by impurities that disrupt the crystal structure, but they are not fragile when pure).
A typical example of a semi-metal is carbon as graphite. Graphite has free electrons and it is a good electric conductor, but it is easily broken by any attempt to deform it.
Elemental bismuth is similar to graphite. It has free electrons, but like graphite, its crystal structure is made of planes of atoms between which there are relatively large distances, so it is fragile like graphite.
The fact that neither bismuth nor graphite are metals, but only semi-metals, is determined by the fact that they have a much higher electro-negativity than metals. The electro-negativity of bismuth is similar to silicon, germanium and antimony (which are also not metals, Si and Ge are semiconductors, while antimony is a semi-metal), and higher than for any true metals. (Semiconductors differ from semi-metals by not having free electrons when pure and at low temperatures; free electrons are produced in semiconductors by various means, e.g. high temperatures, impurities, light, injection etc.)
So the existence of aromatic rings made of bismuth atoms is much less surprising than the existence of aromatic rings made of truly metallic atoms would be.
Despite the fact that the distinction between metals and semi-metals has already been done for almost 300 years, many modern chemistry manuals fail to distinguish them in a consistent way (or worse, some confuse semi-metals with semiconductors). This is a serious mistake, because in practical applications the distinctions between metals, semi-metals and semiconductors are very important. Many technically important materials are semi-metals, for instance many of the carbides or nitrides of the transitional metals.
Even if useful definitions for the terms "metal" and "semi-metal" are 300 years old, as I have said, many modern manuals either do not give any proper definition for the term "metal", or even if they do they do not follow it consistently, so sometimes they apply the word "metal" to substances like bismuth, whose only resemblance to a metal is having free electrons. If this rule were followed consistently, graphite would also have to be named "metal", but no manual does that.
While having free electrons may be the most important property of metals for electrical and electronics engineering, for mechanical engineering and for manufacturing any kind of devices, the other property of metals, ductility, is far more important. This is why the distinction between ductile metals and intrinsically fragile semi-metals is very important.
In this case, the use of the word "metal" for bismuth is a clear cause of confusion, as it suggests an aromatic ring made of electro-positive atoms, which would be a real surprise. An aromatic ring made of atoms with the electro-negativity of bismuth is no surprise.
The elements with high electro-negativity, which in elemental form are semi-metals, semiconductors or non-metals, form covalent bonds between their atoms.
The elements with low electro-negativity, which in elemental form are true metals, form metallic bonds between their atoms.
So the expected chemical behavior for "metals" and for "semi-metals" is quite different.
in another sense, however, it would also make sense to call it and every other element heavier than helium "metal"; since that is how things are done in astronomy, where the arguably most important elements are the first ones.
But when one reads "metal" without any other context, one generally interprets the term within the context of chemistry, where bismuth is absolutely referred to as a "metal", a "post-transition metal" to be more precise.
That is to say, you are the botanist showing up and calling the tomato a fruit, wheras the rest of the world understandably calls it a vegetable.
Another nit: Astronomy, not astrology.
Nevertheless, some classifications are much more useful than others.
A classification that no longer uses the traditional distinction between metals and semi-metals is much less useful than a classification that distinguishes these 2 categories. Neglecting this distinction demonstrates a lack of understanding about which are the properties that determine the usefulness for practical applications of the chemical substances and a lack of understanding of how such properties vary with the atomic number.
Moreover, after one chooses some classification rules, those must be followed consistently. For example, anyone who chooses to call bismuth as a "metal" must also call carbon as a "metal", because the most stable state of carbon in normal conditions, i.e. graphite, has exactly as much reasons to be named as a "metal" or as a "post-transition metal" as bismuth has. There are a very large number of chemical compounds that are semi-metals, but among the pure elements carbon, antimony and bismuth are semi-metals (while boron, silicon, germanium, selenium and tellurium are semiconductors).
The reality is that too many authors of manuals just copy and paste automatically texts from other works without stopping to think whether they are correct and consistent.