Study on ethyl groups with two different orientations in [N(C2H5)4]2CuBr4

•Structural geometry near TC.•Tumbling motion.•Two inequivalent ethyl (1) and ethyl (2).

The crystal structure and phase transition temperature of [N(C2H5)4]2CuBr4 are studied using X-ray diffraction and differential scanning calorimetry (DSC); measurements revealed a tetragonal structure and the two phase transition temperatures TC of 204 K and 255.5 K. The structural geometry near TC is discussed in terms of the chemical shifts for 1H magic angle spinning (MAS) nuclear magnetic resonance (NMR) and 13C cross-polarization (CP)/MAS NMR. The two inequivalent ethyl groups are distinguishable by the 13C NMR spectrum. The molecular motions are discussed in terms of the spin–lattice relaxation times T1ρ in the rotating frame for 1H MAS NMR and 13C CP/MAS NMR. The T1ρ results reveal that the ethyl groups undergo tumbling motion, and furthermore that the ethyl groups are highly mobile.

Graphical abstractLine width of 13C cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) in [N(C2H5)4]2CuBr4 as a function of temperature. Inset: 13C CP/MAS NMR spectrum in [N(C2H5)4]2CuBr4 at 300 K.Figure optionsDownload full-size imageDownload as PowerPoint slide