Nitrido bonding

Table 1 Selected metal-nitrido bond distances and stretching frequencies for ruthenium and osmium...

Schoffel J, Rogachev AY, DeBeer George S, Burger P. Isolation and hydrogenation of a complex with a terminal iridium-nitrido bond. Angew Chem Int Ed Engl. 2009 48 4734-4738. 

W. A. Nugent and J. M. Mayer, Metal-Eigand Multiple Bonds The Chemistry of Transition Metal Complexes Containing Oxo, Nitrido, Imido, Jilkylidene, orJilkylidyne Eigands,Jolm. Wiley Sons, Inc., New York, 1988. Contains electronic and molecular stmcture, nmr, and ir spectroscopy, reactions, and catalysis. 

The most important members of this class are the osmium nitrido, and the osmyl complexes. The reddish-purple K2[OsNCl5] mentioned above is the result of reducing the osmiamate. The anion has a distorted octahedral structure with a formal triple bond Os=N (161pm) and a pronounced /ram-influence (pp. 1163-4), i.e. the Os-Cl distance trans to Os-N is much longer than the Os-Cl distances cis to Os-N (261 and 236 pm respectively). The anion [OsNCls] also shows a rram-effect in that the Cl opposite the N is more labile than the others, leading, for instance, to the formation of [Os NCl4] , which has a square-pyramidal structure with the N occupying the apical position. 

Boschi A, Duatti A, Uccelli L (2005) Development of Technetium-99m and Rhenium-188 Radiopharmaceuticals Containing a Terminal Metal-Nitrido Multiple Bond for Diagnosis and Therapy. 252 85-115... 

Complex 10 is prepared by substitution of [TcNBr2(PPh3 )2]. The Tc-N bond length of the tertiary amine N atom coordinated trans to the nitrido ligand is 2.47(1) A and of the pyridine N atoms coordinated cis is 2.141 av. A. The thioether sulfur atom is not coordinated in the solid, but the H NMR spectrum shows that in solution there is an equilibrium between the dibromo form and one in which Br is expelled and the thioether sulfur is coordinated [62]. 

Fig. 3. The Chatt cycle with its intermediates. The cycle is divided in three stages (a) protonation of bound N2, (b) cleavage of the N-N bond, releasing one molecule of NH3, and (c) reduction and protonation of nitrido complexes generating the second molecule of NH3.

After cleavage of the N-N bond the parent dinitrogen complex has been converted to a Mo(IV) or W(IV) nitrido or imido complex... 

Trends in metal-nitrogen bonding can be illustrated by series of nitrido (H3MN, M = W, Os) and imido (H3MNH, M = Ta, Re, Ir) complexes, isovalent counterparts... 

Table 4.21. Geometrical and NBO parameters for nitrido and imido complexes (4.65), showing bond angles, valence Lewis accuracy (%p f, and metal bond hybrid Qim) and polarization (%cyf) of omn, 7Tmn, and omh NBOs... 

Fig. 2. Significant molecular orbitals of terminal transition metal-oxo units in a six-coordinate 4 ligand environment. The d° configuration is a formal triple bond. The highest occupied molecular orbital in the d configuration is formally nonbonding (8 symmetry) so the metal-oxo bond order remains 3.0. However, d-electron counts above d populate orbitals that are antibonding between the metal and the terminal multiply bonded ligand (0x0 in this case, but alternatively, alkyl-imido, nitrido, sulfido, etc.). Note that all the equatorial ligand orbitals and the metal dx2 y2 orbital (hi in 4 symmetry) are ignored for simplicity.

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