Characterization of the Crystalline and Solution Phases in N,N‘-Dimethylethylenediamine (DMEDA) with Sodium Triflate (NaCF3SO3)

Abstract

Linear poly(ethylenimine), [LPEI], is a synthetically versatile polymer host compared to poly(ethylene oxide), in that various groups can be attached to the backbone nitrogen atoms. The interactions of LPEI with sodium cations are modeled by solutions of N,N‘-dimethylethylenediamine, DMEDA, containing dissolved sodium triflate [NaTf]. During these studies, the crystalline compound (DMEDA)2(NaTf)5 was discovered and characterized by X-ray diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy, and Raman spectroscopy. The compound crystallizes in polymeric chains in a triclinic unit cell of the P1̄ space group. In the crystal, the sodium ions are both five- and six-coordinate. A spectroscopic comparison of DMEDA, the (DMEDA)2(NaTf)5 crystal, and (DMEDA)xNaTf solutions over a composition range of 7.5:1 to 1.5:1 [DMEDA:NaTf, molar ratio] was conducted using infrared and Raman spectroscopy. In (DMEDA)2(NaTf)5, the triflate ions vibrate as either [Na2Tf]+ or [Na3Tf]2+ species due to the coordination of the triflate ion by sodium ions. However, in solution, only the [Na2Tf]+ species is present at high NaTf compositions. At a 7.5:1 DMEDA/NaTf composition, contact ion pairs [NaTf] are the dominant species.