Preparation, Characterization, X-ray Crystal Structure, and Energetics of Cesium 5-Cyano-1,2,3,4-Tetrazolate: Cs[NCCNNNN]

Cesium 5-cyano-1,2,3,4-tetrazolate, (Cs1), was prepared in 100% yield by a 3 + 2 cycloaddition
reaction of CsN3 and (CN)2 in SO2. Cs1 forms monoclinic crystals (a = 8.297(2) Å, b = 11.040(3) Å, c =
6.983(2) Å, β = 120.31(2)°, space group C2/c, Z = 4, R1 = 0.048, wR2 = 0.120 for 1217 independent reflections).
Cs1 is best described as a three-dimensional array of cations and anions connected by weak Cs+−Nδ- contacts.
The cations and anions each form a diamond-type lattice (tetrahedral arrangement of ions) with the counterions
lying in hexagonal channels running parallel to the c-axis. The anions in the channels form stacks with the CN
groups pointing in opposite directions in adjacent layers. The calculated (RB3PW91/6-311+G*) geometry of 1
is in agreement with the X-ray crystal structure, and the calculated vibrational spectrum is in good agreement
with the observed FT-IR and FT-Raman spectra. The lattice enthalpies and heats of formation of M1 (M = Cs,
K) as well as the enthalpy of formation from MN3(s) and (CN)2(g) were estimated. The 13C and 14N NMR spectra
of Cs1 are also reported. The ionization potential (450.7 kJ mol) and electron affinity (427.4 kJ/mol) of 1 were
calculated. Attempts to oxidize 1 with AsF5 led to the formation of Cs1·xAsF5 (x ≈ 2). The 7π dianion
is calculated to be a stable entity in the gas phase, but Cs21 is estimated to be unstable with
respect to dissociation to 2 CsCN and 3/2 N2 (ΔHdiss = −132.4 kJ/mol). The preparation of the potassium salt of
1 and the corresponding thermodynamic quantities are reported.