SCIENTIFIC EDUCATIONAL CENTER science idea

Chemists from the USA and Germany synthesized a compound capable of decomposing to form phosphorus mononitride PN. The resulting mononitride quickly turned into a polymer, but chemists managed to intercept it with an iron complex. As a result, a complex compound was formed with phosphorus mononitride as a ligand.

The molecules of phosphorus mononitride PN are similar in electronic structure to nitrogen molecules N2, but, unlike nitrogen, it is very difficult to observe the formation of phosphorus mononitride. Physicists were the first to do this in 1933: they passed an electric discharge through a tube containing phosphorus residues from a previous experiment. In the mass spectrum of the resulting gas, scientists noticed a peak corresponding to the compound with the formula PN. Then, in 1977, the mononitride was characterized using IR spectroscopy - this required a matrix of solid krypton in which the molecules of this compound could exist for a long time.

It has not yet been possible to obtain mononitride in its pure form in the laboratory due to the fact that it polymerizes very quickly. Despite the fact that scientists have already obtained many potential precursors of mononitride with a phosphorus-nitrogen bond, it has not yet been possible to reliably observe the formation of PN during the decomposition of these compounds.

Chemists led by Christopher C. Cummins from the Massachusetts Institute of Technology decided to synthesize another compound with a phosphorus-nitrogen bond, in order to then try to get phosphorus mononitride from it. They took disubstituted chlorophosphine and mixed it with sodium azide and lithium chloride in tetrahydrofuran. As a result, the chlorine in phosphine was replaced by an azide group, and insoluble sodium chloride precipitated. So scientists obtained the source for the synthesis of phosphorus mononitride — phosphinoazide, and the reaction yield was 70 percent.

Then the chemists tried to find out the melting point of phosphinoazide, but when they heated it to 68 degrees Celsius, an explosion occurred. Then the scientists decided to find out what is formed during the decomposition of this compound, and heated it at reduced pressure. Analysis of a mixture of gaseous products using mass spectrometry showed that organic fragments, nitrogen and rapidly polymerizing phosphorus mononitride are formed during decomposition. So chemists were able to observe the formation of phosphorus mononitride during the decomposition of phosphinoazide.

Then, to obtain a metal complex with phosphorus mononitride, the scientists mixed phosphinoazide with a semi-sandwich iron complex that contained molecular nitrogen as a ligand. Chemists assumed that phosphinoazide would slowly decompose, releasing phosphorus mononitride, and it, in turn, would replace nitrogen in the iron complex. And so it happened: after an hour of mixing, chemists isolated an iron complex with phosphorus mononitride from the reaction mixture and found out its structure using X-ray structural analysis.

It turned out that phosphorus mononitride is bound to iron by a nitrogen atom, although chemists thought that the binding would occur through phosphorus. Computer calculations have shown that the bond with nitrogen is more energetically advantageous due to the weaker exchange interaction between the electron shells of nitrogen and iron atoms.

So chemists were able to detect phosphorus mononitride during the decomposition of organic phosphinoazide, which they synthesized with a yield of 70 percent. The authors of the article believe that the synthesized azide will allow a more detailed study of the properties of unstable nitride.

The article was published in the journal Nature Chemistry

PHOTO: Appearance of crystals of phosphorus mononitride complex with iron © C. Cummins et al. / Nature Chemistry, 2022
Source: Mikhail Boym nplus1.dev, sci-dig.ru

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