Synthesis, microwave spectra, x-ray structure, and high-level theoretical calculations for formamidinium formate

An efficient synthesis of formamidinium formate is described. The experimental x-ray structure shows both internal and external H-bonding to surrounding molecules. However, in the gas phase, this compound occurs as a doubly hydrogen bonded dimer between formamidine and formic acid. This doubly hydrogen-bonded structure is quite different from the solid state structure. Microwave spectra were measured in the 6-14 GHz range using a pulsed-beam Fourier transform microwave (MW) spectrometer. The two nonequivalent N-atoms exhibit distinct quadrupole coupling. The rotational, centrifugal distortion, and quadrupole coupling constants determined from the spectra have the following values: A = 5880.05(2), B = 2148.7710(2), C = 1575.23473(13), 1.5 χaa (N1) = 1.715(3), 0.5(χbb–χcc) (N1) = −1.333(4), 1.5 χaa (N2) = 0.381(2), 0.25(χbb–χcc) (N2) = −0.0324(2), and DJ = 0.002145(5) MHz. The experimental inertial defect, Δ = −0.243 amu A2, is consistent with a planar structure. Accurate and precise rotational constants (A...