The Binary Group 4 Azides [PPh₄]₂[Zr(N₃)₆] and [PPh₄]₂[Hf(N₃)₆]

Abstract

The binary zirconium and hafnium polyazides [PPh ] [M(N ) ] (M=Zr, Hf) were obtained in near quantitative yields from the corresponding metal fluorides MF by fluoride-azide exchange reactions with Me SiN in the presence of two equivalents of [PPh ][N ]. The novel polyazido compounds were characterized by their vibrational spectra and their X-ray crystal structures. Both anion structures provide experimental evidence for near-linear M-N-N coordination of metal azides. The species [M(N ) ], [M(N ) ] and [M(N ) ] (M=Ti, Zr, Hf) were studied by quantum chemical calculations at the electronic structure density functional theory and MP2 levels.

The Binary Group 4 Azide Adducts [(bpy)Ti(N3)4], [(phen)Ti(N3)4], [(bpy)2Zr(N3)4]2·bpy, and [(bpy)2Hf(N3)4]2·bpy

“…The average Zr–N–N angle of 135.9(2)° and average N–N distances of the azido ligands of 1.211(6) Å (internal) and 1.127(6) Å (terminal) are typical values for covalent azido compounds. The average metal‐nitrogen distance for the azido ligands in [(bpy) 2 Hf(N 3 ) 4 ] is 0.024(5) Å shorter than in [(bpy) 2 Zr(N 3 ) 4 ] but in good agreement with the Hf–N azide distances in the [Hf(N 3 ) 6 ] 2– anion and with typical Hf–N distances reported in the literature . A similar trend is observed for the average Hf–N bpy distance which is 0.028(5) Å shorter than the average Zr–N bpy distance in [(bpy) 2 Zr(N 3 ) 4 ].…”

“…Both squares are elongated along the N bpy –N bpy diagonal. In the [(bpy) 2 M(N 3 ) 4 ] molecule, the average Zr–N azide distance of 2.172(5) Å is larger than in [Zr(N 3 ) 6 ] 2– {2.150(3) Å} . The average Zr–N bpy distance of 2.502(8) Å is in good agreement with typical Zr–N distances reported in the literature .…”

“…A similar trend is observed for the average Hf–N bpy distance which is 0.028(5) Å shorter than the average Zr–N bpy distance in [(bpy) 2 Zr(N 3 ) 4 ]. A slight decrease of M–N distances of hafnium over zirconium has also been observed for the related hexaazidometallates . The average Hf–N–N angle of 136.3(2)° and average N–N distances in the azido ligands of 1.205(4) Å (internal) and 1.148(4) Å (terminal) are again typical values for covalent azido compounds.…”

“…Partially azido‐substituted titanium and zirconium compounds have been reported more than 30 years ago, while the first binary titanium polyazides [Ti(N 3 ) 4 ], [Ti(N 3 ) 5 ] – and [Ti(N 3 ) 6 ] 2– were prepared in 2004 . More recently, the syntheses and crystal structures of the binary zirconium and hafnium azides [PPh 4 ] 2 [Zr(N 3 ) 6 ] and [PPh 4 ] 2 [Hf(N 3 ) 6 ] were reported . Based on quantum chemical calculations, the metal tetraazides [M(N 3 ) 4 ] (M = Ti, Zr, Hf) were predicted to exhibit tetrahedral structures with unique linear M–N–N bonds.…”

Manganese‐Mediated Linkage of Perchlorate to Aminotetrazoles Produces Twice the Energy Density of the Unmetalated Salt

“…To introduce more energy into energetic materials, we have been exploring the introduction of non‐CHNO (or “inorganic”) atoms into energetic materials. Complexes of azides with metals are of use as primary explosives, and related complexes have been explored as a means of generating novel nitrogen‐rich molecules, and metal–organic frameworks (MOFs) . Relevant to this report are recent examples of manganese complexes and clusters of tetrazole systems…”