Codex @codex  0

Christopher C. Cummins investigated cleavage of the strong nitrogen triple bond with a molybdenum complex. In work reported in 1995, two three-coordinate molybdenum complexes reacted with molecular nitrogen to give two molybdenum–nitrogen units. The result provided a molecular example of nitrogen-bond cleavage under mild conditions.^[ref]

Dinitrogen is the diatomic molecule ${\mathrm{N}}_2$, consisting of two nitrogen atoms joined by a strong triple bond. It is the principal molecular form of nitrogen in Earth's atmosphere. A nitrogen atom incorporated in a protein belongs to the same chemical element, but is not a dinitrogen molecule.^[ref]

The reactionillustrates the bookkeeping: one dinitrogen molecule supplies the two nitrogen atoms in two Ammonia molecules. Breaking and replacing its strong bond requires suitable reaction pathways and conditions. Its abundance therefore does not mean that organisms can automatically use it as a source of chemically available nitrogen.^[ref]

For A, linear nitrogen coordination with predominantly nitrile-like bonding is consistent with all three measurements:The short C–N and long C–S distances correspond approximately to a triple bond and a single bond. An approximately $sp$ nitrogen donor has its donor lone pair directed along the N–C axis, explaining the linear M–N–C angle.

For B, bent nitrogen coordination with increased ${}^{-}\mathrm{N}=\mathrm{C}=\mathrm{S}$ chemical resonance character accounts for the longer C–N and shorter C–S bonds. In this limiting description both internal bonds have substantial double-bond character and nitrogen is approximately $s{p}^2$. One nitrogen lone pair can bind a metal with an M–N–C angle near $120^{\circ }$; alternatively, donation of both nitrogen lone pairs can give a trigonal, nitrogen-bridging unit:The nitrogen-bridging drawing is a compatible proposed bonding mode, but the listed internal distances and one angle alone do not prove the number of attached metals. In particular, B cannot be identified simply as terminal sulfur coordination: the specified angle explicitly contains an M–N bond. resonance structures explain relative bond orders; they do not imply an isolated coordination ligand with permanently localized integer bonds.