A novel mononuclear metal-organic compound, [Cu-(Hdabco)(H2O)Cl-3] (1, dabco = 1,4-diazabicyclo[2.2.2]octane) in which the Cu-II cation adopts a slightly distorted bipyramidal geometry where the three Cl anions constitute the equatorial plane and the Hdabco cation and H2O molecule occupy the two axial positions, was synthesized. Its paraelectric-to-ferroelectric phase transition at 235 K (T-c) and dynamic behaviors were characterized by single crystal X-ray diffraction analysis, thermal analysis, dielectric and ferroelectric measurements, second harmonic generation experiments, and solid-state nuclear magnetic resonance measurements. Compound 1 behaves as a molecular rotor above room temperature in which the (Hdabco) part rotates around the N center dot center dot center dot N axis as a rotator and the [Cu(H2O)Cl-3] part acts as a stator. In the temperature range 235-301 K, a twisting motion of the rotator is confirmed. Below the T, the motions of the rotor are frozen and the molecules become ordered, corresponding to a ferroelectric phase. Origin of the ferroelectricity was ascribed to relative movements of the anions and cations from the equilibrium position, which is induced by the order disorder transformation of the twisting motion of the molecule between the ferroelectric and paraelectric phases. Study of the deuterated analogue [Cu(Ddabco)(D2O)Cl-3] (2) excludes the possibility of proton ordering as the origin of the ferroelectricity in 1.