Motion of the water molecules and phase transitions in Sr[Fe(CN)₅NO]*4H₂O studied by proton NMR

Abstract

The mobility of the water molecules and the phase transitions in strontium nitroprusside (SrNP) have been studied by proton spin-lattice relaxation time and proton NMR spectra over a wide temperature range. The activation energies for 180° flip motions of three distinct water molecules existing in the unit cell of the SrNP have been determined to be 23·4, 6·69, and 8·37 kJ mol^-1. Four phase transitions at T _c1 = 197 K, T _c2 = 192 K, T _c3 = 182 K and T _c4 = 174 K have been discovered, and some of the nature of these transitions were brought to light.