Azide complex, molecular structure

Fig. 41. (Left) Molecular structure of the azide complex 81 in the crystal. (Right) Central N3Ni(g-S)2( i,3-N3)NiN3 core in 81. The figures were generated using data downloaded from The Cambridge Crystallographic Data Center (CCDC) and correspond to the structure originally reported in Ref. (242).

An organometallie azide complex was obtained by replacement of THF through the azide anion in Cp3Sm(THF) (Eq. 6) [74], The molecular structure exhibits different and comparatively large Sm-N-N angles of 134(1) and 151(1)°. The Sm-N bond lengths of 2.47(2) and 2.48(2) A are comparable to those of the inorganic azides. 

Fig. 1.17 Molecular structures of lead styphnate (LS), lead azide (LA), an iron and copper nitrotet-razolate complexes as well as copper(l) 5-nitrotetrazolate (DBX-1) and potassium-7-hydroxy-6-dini-trobenzofuroxane (KDNP).

FIGURE 18 Top Molecular structure of Rebek s capsule (59) for the acceleration of a 1,3-dipolar cycloaddition between phenylacetylene and phenyl azide. Bottom CAChe-minimized structure of the ternary complex. Symmetrically loaded capsules are also found in solution. (See Color Insert in the back of this book.)... 

A number of structural studies of iminophosphoranes have been reported. These include the product obtained from the reaction of phosphine (bisphosphine sulphide) (31) with p-tolyl azide which on the basis of its iH and iP n.m.r. exists in the C-ylide form (32) rather than as an iminophosphorane.16 Treatment of (32) with base gave the relatively stable iminophosphorane anion (33) which was isolated as a Rh(l) complex. The molecular structures of the iminophosphoranes (34),17 (35),1 and (36)19 have been determined by X-ray crystallography and their structural parameters compared with those determined for l,8-bis(dimethylamino)-... 

FIGURE 5 Molecular structure of the cyanogen azide-arsenic pentafluoride Lewis acid/Lewis base complex, FsAs N=C— NNN. 

Cu(I)-catalyzed 1,3 dipolar cycloaddition of terminal alkynes and azides has emerged as a promising tool for an efficient and easy access of complex molecular-level structures regioselectively in good yields. This coupling technique deals... 

Because the two regioisomeric products 8a and 8b have almost the same molecular dimensions, it is difficult to discriminate between the two isomers with the geometric constraints imposed by the zeolite pores. Considering that calcium ions are apt to form mainly five-membered chelate complexes with polyhydroxy compounds (Fig. 4b) 32,33) and that calcium zeolites have also been employed as sorbents in carbohydrate separations (ii), it is possible to speculate that in the CaY-supported NaN3 system the epoxy alcohol first forms a coordinated structure around a calcium ion, as shown in Fig. 4a, followed by ring opening with an azide anion at the C-3 position of the epoxy alcohol, giving a stable, five-membered chelate complex with the calcium ion. 

In the alkali metal pseudohalides the contribution of cationic wave functions to the valence band structure can be neglected. The optical absorption spectra can therefore be correlated to transitions involving excited states of the anions. However, one can see solid state effects like the superposition of vibronic structure on the molecular symmetry forbidden transition at 5.39 eV in the crystal spectra of the alkali metal azides (76). In the more complex heavy metal and divalent azides, a whole range of optical transitions can occur both due to crystal field effects and the enhanced contributions from cationic states to the valence band. Detailed spectral measurements on a-PbNe (80), TIN3 (57), AgNs (52), Hg(CNO)2 (72) and AgCNO (72) have been made but the level assignments can at best be described as tentative since band structure calculations on these materials are not available at present. 

The physical characterization in terms of phases, crystal structures, and molecular and electronic defects presents a different picture. The inorganic azides, simple though they may be in comparison with most energetic substances, are nonetheless molecularly complex, and the elucidation of the crystal structures has been the subject of investigation for 40 years. In the last decade important refinements to the earlier knowledge have become possible through the combined advances in chemical preparation, neutron diffraction, and computational techniques. The advances are presented in Chapter 3, and their importance to azide research is well illustrated by the frequency with which the information in that chapter is utilized in the other chapters. 

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