J. Am. Chem. SOC.1988, 110, 707-712
707
Structure of Triazadienyl Fluoride, FN3, by Microwave, Infrared, and ab Initio Methods D. Christen,*t H. G. Mack,t G . Schatte,*and H. Willner* Contribution from the Institut fur Physikalische und Theoretische Chemie, Universitat Tubingen. D- 7400 Tubingen, and Institut fur Anorganische Chemie, Universitat Hannover, D- 3000 Hanover, Federal Republic of Germany. Received June 1, 1987
Abstract: Microwave and infrared spectra of the unstable species FN, as well as its various lSN-enrichedisotopomers have been recorded and analyzed, yielding data on molecular structure, dipole moment, and harmonic force constants. The rotational constants for the parent isotopic species are (in MHz) A = 48 131.448, E = 5713.288, C = 5095.276. The dipole moments (D) are fia = 1.1, p b = 0.7, ketal = 1.3. The fundamental frequencies (cm-') are 2037, 1090, 873.5, 658, 241, 504. The diagonal force COnStantS (100 N/m) arefNp, = 17.414,f~"~= 6 . 6 8 6 , f ~ , = ~ 3.753,fm,~ = 1 . 2 4 5 , f ~ , ~ p=, 0.477,fwp = 0.014. The structural parameters are rNF = 144.4, rNaN = 125.3, fN& = 113.2 pm; L F ~ ~ = N 103.8', , LN,N,N, = 170.9'. Ab initio calculations using 6-31G* and MP2/6-31d* basis sets have been carried out to calculate structure, force field, dipole moment, and electric field gradients at the I4N quadrupole nuclei.
Triazadienyl fluoride is one of the most explosive and thermally unstable covalent azides known, and consequently no complete structural or spectroscopic investigations of this molecule have been published until now. All that was known were some theoretical calculations of structural parameters'*2and argon-matrix IR frequencies of a few of the fundamental vibrations3 The recent discovery of a relatively safe synthetic route to the pure substance4 has opened the way for microwave and I R spectroscopic investigations of the substance in the gas phase and also made the synthesis of the '5N-substituted triazadienyl fluorides feasable, which in turn allowed for a complete determination of the structure and harmonic force field. The results are compared with MP2/6-31G* a b initio calculations that also guided the search for the harmonic force field.
Experimental Section Warning! Triazadienyl fluoride is extremely explosive in the liquid and solid states. We recommend 20 mg as the absolute maximum amount of sample to be handled in one batch. The synthetic route to pure FN, is described in ref 4. The main step is the reaction of HN, with F,; thus for the synthesis of ISN-enriched species (Na, N,, N,) one needs correspondingly enriched NaN,, which was obtained in the following way. In a 100" glass vessel with a Teflon stopcock, 40 mg (1.8 mmol) of Na and 3.5 mmol of I5NH, (95%, A. Hempel GmbH, Diisseldorf) were reacted for 2 h at 350 'C to yield NaI5NH2. The evolving hydrogen was pumped through a cold trap kept at -196 OC to recover excess "NH,. Thereafter, 2 mmol of N 2 0 was condensed into the vessel, and the mixture was heated to 150 OC for 12 h. The NalsNNN that was formed was dissolved in water, filtered, and neutralized (pH 9) with dilute H2S04before it was dried at 90 'C. The terminal nitrogens are equivalent in ionic azides; thus NaISNNN is the precursor of both FISNNN and FNNISN. In order to substitute the central nitrogen in NaNNN with 15N, 1.2 mmol of NaNH2 was reacted with 1 mmol of lSNNO (98%, A. Hempel GmbH, Diisseldorf) as described above. The microwave and IR matrix investigation showed that small amounts (
