Some ionic compounds (salts) form liquids when heated to temperatures in the range of 200-300 degrees C. They may be referred to as moderate temperature ionic liquids. An example of such a compound is the 1,1,3,3-tetramethylguanidinium chloride, [TMGH]Cl, melting at similar to 212 degrees C. The chemistry of this compound-containing a dimeric ion-pair "molecule"-was investigated in the solid state, in solutions in water and ethanol, and in the vapor phase, based on ab initio molecular orbital density functional theory (DFT)-type calculations with 6-311+G(d,p) basis sets. Calculations on the monomeric [TMGH]l ion and the dimeric chloride ion-pair salt converged to give geometries near the established crystal structure of [TMGH]Cl. The structures and their binding energies are given as well as calculated vibrational harmonic normal modes (IR and Raman band wavenumbers and intensities). Experimentally obtained Raman scattering spectra are presented and assigned, by comparing to the quantum mechanical calculations. It is concluded that dimeric molecular ion pairs with four N-H+center dot center dot center dot Cl- hydrogen bonds probably exist in the solutions and are responsible for the relatively high solubility of the "salt" in ethanol. It was discovered that the compound can be easily sublimed by heating to about 200-230 degrees C. In the Raman spectrum of the vapor at 225 degrees C, a characteristic strong band at 2229 cm(-1) was found and interpreted to show that the gas phase consists of monomeric ion-pair "molecules" held together by a single N-H+center dot center dot center dot Cl- hydrogen bond, the stretching band of which is causing the band.