Methods
Safety precautions Caution.
NaN5 and other metal–N5 complexes are, in part, extremely energetic compounds with increased sensitivities towards various stimuli, therefore proper
protective measures (safety glasses, face shield, leather coat, earthen equipment and shoes, Kevlar gloves and ear plugs) should be used. All
compounds should be stored in explosive cases as they can explode spontaneously.
General methods.
All reagents and solvents were purchased from Sigma-Aldrich, Aladdin, and Energy Chemical as analytical grade and were used as received. The
filtration and storage of the intermediate product were performed in a Coolingway DW-86W58 cryopreservation box. A Bruker AVANCE 500 nuclear magnetic
resonance spectrometer operating at 50.69 MHz was used to collect 15N spectral data. DMSO-d6 and CD3OD were employed as the solvent and locking
solvent, respectively. Chemical shifts are given relative to MeNO2 for 15N NMR. High-resolution mass spectra (electrospray ionization) were recorded
on a Waters Q-TOF MicroTM high-resolution mass spectrometer operated in the splitless mode. The samples were dissolved in methanol/H2O (70/30 by
volume), and introduced via a syringe pump at 5 μl min−1. The instrument was run in the negative ion mode with a capillary voltage of 2,500 V. DSC
plots were acquired on a differential scanning calorimeter (Mettler Toledo DSC-1) at a scan rate of 5 °C min−1 in perforated stainless steel
containers under a nitrogen flow of 50 ml min−1. TG analysis was also performed at a heating rate of 5 °C min−1 on a Mettler Toledo TGA/SDTA851e
instrument. X-ray photoelectron spectroscopy (XPS, XPS Microprobe, PHI Quantera II) was performed using Al Kα as a monochromatic radiation source
(hν = 1,486.7 eV) at a power of 240 W (12 kV × 20 mA) at 25 °C. The total pressure in the main vacuum chamber during analysis was typically 5 ×
10−8 Pa. The pass energy was set to 160 eV (energy step 0.5 eV) for recording survey spectra and 20 eV (energy step 0.05 eV) for high-resolution
spectra. The carbon peak at 285.0 eV was used as a reference to correct for charging effects. IR spectra were recorded on a Thermo Nicolet IS10
instrument. Raman spectra were collected using a Horiba-Jobin Yvon Labram HR800 Raman spectrometer with a 514.532 nm Ar+ laser. A 50× objective was
used to focus the laser beam. TG–DSC–MS was performed on a Netzsch STA 449 F3 Jupiter and QMS 403C at a heating rate of 5 °C min−1 under an
argon atmosphere.
[Na(H2O)(N5)]·2H2O (2)
To a magnetically stirred H2O/tetrahydrofuran mixed solution (20 ml/20 ml) containing 4-hydroxy-3,5-dimethylbenzenaminium chloride31 (6 g, 34.58 mmol)
and hydrochloric acid (36%, 3.025 ml, 36.31 mmol), sodium nitrite (2.505 g, 36.31 mmol) in 5 ml water was added dropwise at −3 to 0 °C. After 45
min, 45 ml methanol and 45 ml THF were added and the reaction system was cooled to −38 °C, after which sodium azide (2.360 g, 36.31 mmol) in
methanol/H2O (22 ml, 1/1 by volume) was added dropwise. The resulting mixture was stirred at −38 °C for 1.5 h. The solution was removed by
filtration at −60 °C (in a cryopreservation box), and the filter residue was washed with acetone (10 ml × 4). The off-white solid was collected
and used in the next step without further purification after freeze-drying. A solution of the intermediate product sodium salt of arylpentazole (5.000
g, 21.64 mmol) and ferrous glycinate (8.600 g, 42.16 mmol) in a mixed solution of 100 ml methyl alcohol and 100 ml acetonitrile was stirred at −47
°C. After 30 min, meta-chloroperbenzoic acid (85%, 19.25 g, 94.82 mmol) was added in portions. The reaction mixture was maintained at –43 °C for
24 h. The precipitate was removed by filtration, and the filtrate was evaporated under reduced pressure. The residue was suspended in 200 ml of water,
after which the precipitate was filtered off and washed with 50 ml water. The filtrate was concentrated, and after removing the solvent under vacuum,
the residue was purified by chromatography with ethyl alcohol/ethyl acetate (1/10–1/3 gradient elution). Crude NaN5 hydrate was obtained as an
off-white product (427 mg, 19.56%). Colourless crystals of 2 were obtained by maintaining alcohol (95%) solutions at ambient temperature for several
days. Decomposition point (onset): 111.3 °C; 15N NMR (50.69 MHz, DMSO-d6): δ − 5.7 p.p.m. (s); IR (neat): νmax 3,491, 3,354, 3,293, 2,166, 1,651,
1,246, 1,219 cm−1; Raman (neat): νmax 1,188, 1,120, 1,005, 112 cm−1; HRMS (m/z): [M]− calcd for N5, 70.0154; found, 70.0156; analysis (% calcd,
% found for NaH6N5O3): H (4.08, 4.13), N (47.62, 47.74).
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