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Transition metal azide complex
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Transition metal azide complex
Transition metal azide complexes are coordination complexes containing one or more azide (N3−) ligands. In addition to coordination complexes, this article summarizes homoleptic transition metal azides, which are often coordination polymers.
Azide is a pseudohalide but more nucleophilic than chloride, as reflected by the higher pKa of hydrazoic acid (4.6) vs hydrochloric acid (-5.9). As a monodentate ligand, azide binds through one of the two terminal nitrogen atoms, i.e. M-N=N=N. Azide is a "pure" sigma donor. It is classified as an X ligand in the Covalent bond classification method. In the usual electron counting method, it is a one-electron ligand.
The N3 unit is linear or nearly so. The M-N-N angles are quite bent. Azide functions as a bridging ligand via two bonding modes. Commonly the metals share the same nitrogen ("N-diazonium" mode). Less common is the motif M-N=N=N-M, illustrated by [Cu(N3)(PPh3)2]2.
Traditionally, metal azide complexes are prepared by salt metathesis, e.g. the reaction of metal chlorides with sodium azide. In some cases, trimethylsilyl azide is employed as the azide source. Another popular route include acid-base reactions hydrazoic acid HN3 and either hydrido or lewis base complexes. Still other methods rely on halide-azide exchange with trimethylsilyl azide SiMe3N3 with the metal fluorides as incomplete halide/azide exchange is often seen when using the chloride derivatives.
Many homoleptic complexes (with only one kind of ligand) are known. Coordination numbers range from 2 (e.g., [Au(N3)2]−) to 7 (e.g., [W(N3)7]−). Many homoleptic complexes are octahedral anions of the type [M(N3)6]n-:
For some metals, homoleptic complexes exist in two oxidation states: [Au(N3)2]− vs [Au(N3)4]− and [Pt(N3)6]2- vs [Pt(N3)4]2-.
Binary azide compounds can take on several structures including discrete compounds, or one- two, and three-dimensional nets, leading some to dub them as "polyazides". Reactivity studies of azide compounds are relatively limited due to how sensitive they can be.
Neutral unsolvated group 3 polyazide is only known for divalent europium(II) compound, Eu(N3)2. Attempts to react lanthanide hydroxides with HN3 result in their basic azides, Ln(OH)(N3)2 or Ln(OH)2N3.
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Transition metal azide complex
Transition metal azide complexes are coordination complexes containing one or more azide (N3−) ligands. In addition to coordination complexes, this article summarizes homoleptic transition metal azides, which are often coordination polymers.
Azide is a pseudohalide but more nucleophilic than chloride, as reflected by the higher pKa of hydrazoic acid (4.6) vs hydrochloric acid (-5.9). As a monodentate ligand, azide binds through one of the two terminal nitrogen atoms, i.e. M-N=N=N. Azide is a "pure" sigma donor. It is classified as an X ligand in the Covalent bond classification method. In the usual electron counting method, it is a one-electron ligand.
The N3 unit is linear or nearly so. The M-N-N angles are quite bent. Azide functions as a bridging ligand via two bonding modes. Commonly the metals share the same nitrogen ("N-diazonium" mode). Less common is the motif M-N=N=N-M, illustrated by [Cu(N3)(PPh3)2]2.
Traditionally, metal azide complexes are prepared by salt metathesis, e.g. the reaction of metal chlorides with sodium azide. In some cases, trimethylsilyl azide is employed as the azide source. Another popular route include acid-base reactions hydrazoic acid HN3 and either hydrido or lewis base complexes. Still other methods rely on halide-azide exchange with trimethylsilyl azide SiMe3N3 with the metal fluorides as incomplete halide/azide exchange is often seen when using the chloride derivatives.
Many homoleptic complexes (with only one kind of ligand) are known. Coordination numbers range from 2 (e.g., [Au(N3)2]−) to 7 (e.g., [W(N3)7]−). Many homoleptic complexes are octahedral anions of the type [M(N3)6]n-:
For some metals, homoleptic complexes exist in two oxidation states: [Au(N3)2]− vs [Au(N3)4]− and [Pt(N3)6]2- vs [Pt(N3)4]2-.
Binary azide compounds can take on several structures including discrete compounds, or one- two, and three-dimensional nets, leading some to dub them as "polyazides". Reactivity studies of azide compounds are relatively limited due to how sensitive they can be.
Neutral unsolvated group 3 polyazide is only known for divalent europium(II) compound, Eu(N3)2. Attempts to react lanthanide hydroxides with HN3 result in their basic azides, Ln(OH)(N3)2 or Ln(OH)2N3.
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