J. Am. Chem. Soc. 1992, 114, 3411-3414
341 1
New Synthesis, Crystal Structure, and Vibrational Spectra of Tetramethylammonium Azide and Reactions of the Fluoride Anion with HN3 and of the Azide Anion with HFt Karl 0. Christe,*v*William W. Wilson,* Robert Bau,s and Steven W. Buntes Contribution from Rocketdyne, A Division of Rockwell International Corporation, Canoga Park, California 91 303, and The Department of Chemistry, University of Southern California, Los Angeles, California 90007. Received October 15, 1991 Abstract: Tetramethylammonium azide, N(CH3)?+N3-, was obtained in high purity and quantitative yield by the reaction of N(CH3),+F with Si(CH3)3N3in CH3CN solution. This compound is isostructural with N(CH3),+HF2- and crystallizes in the orthorhombic system: space group, Pmr12~(No. 31); a = 6.879 (5) A; b = 5.479 (4) A; c = 8.858 (7) A; Z = 2; R(F) = 0.0388. Its N3- anion is symmetric and linear and the N(CH3)4+cation is somewhat distorted from tetrahedral symmetry due to crystal packing effects. The infrared and Raman spectra of N(CH3)4+N3-were also recorded. The symmetric stretching mode of N3- exhibits the pronounced frequency decrease expected for increasing ionicity with increasing cation size. A study of the HN,-MF systems [M = Na, K, Rb, Cs, N(CH3),] revealed some unexpected chemistry. Even at -80 OC, H N 3 displaces F from M F with formation of equimolar amounts of M+N3- and HF. The latter reacts with M F to give M+HF2-. On the other hand, H F quantitatively displaces N3- from M N 3 with formation of HN3 and M'HF,. This apparent discrepancy can be explained by the vast difference in basicity between F and HF2-. Attempts to isolate stable F-H-N3- or N3-H-N3- anions from H N , and either M F or MN3, respectively, were unsuccessful. Introduction
Table I. Summary of Crystal Data and Refinement Results for
Although tetramethylammonium azide, N(CH,),+N,-, had been known' since 1918, only very little information has since been reported2" for this interesting compound. According to t h e previous reports,l4 the compound was prepared by either the reaction of N(CHJ41 with AgN, (1) in either water' or anhydrous
N(CH3)4+NC space group a (A) b (A) c
molecules/unit cell formula weight (g/mol) crystal dimens (mm) calcd density (g cm-)) wavelength (A) used for data collecn sin (el?,)limit (.&-I) total no. of reflecns measured no. of independent reflecns no. of reflecns used in structural analysis, I>3 4 ) no. of variable params final agreement factor
ethanol4 or the n e u t r a l i z a t i ~ n ~of* N ~ ,(~C H 3 ) , 0 H with aqueous HN3 (2). Both preparations involve the use of shock-sensitive N(CH3)40H
+ HN3
-
N(CH3),N3
+ H,01
(2)
starting materials, i.e. AgN, and HN3,and suffer from solubility and purification problems. N o structural or spectroscopic data had previously been reported for N(CH3),N3, except for partial vibrational In this paper, we report an improved synthesis for N(CH3),N3 and its crystal structure and vibrational spectra.
Experimental Section Caution! Hydrazoic acid is shock sensitive when undiluted, and appropriate shielding and safety precautions must be used when working with this compound. Materials. CH3CN (Baker, Bio-analyzed, having a water content of 40 ppm) was treated with P205and freshly distilled prior to use, thereby reducing its water content to
