Structure of putrescinium dinitrate at three low temperatures (30, 120 and 275 K)

Abstract

The X-ray structure of putrescinium dinitrate (1,4butanediammonium dinitrate, C4HI4N~+.2NO3, M r = 214.2) has been studied by X-ray diffraction at 30, 120 and 275 K and compared with the structure previously determined at room temperature (291 K). In this range of temperatures the crystals triclinic, P], with Z= 2. The unit-cell parameters at 30K are a = 8.5478 (4), b = 5.4927 (2), c-- 10.2563 (5) A, = 91.664 (4), fl= 93.572 (3), y--- 103.337 (4) ° , V= 467.17 (4)A 3, R = 0.034 for 2490 observed reflexions. The unit cell contains two centrosymmetric putrescinium dications located on two different inversion centers. Cation I has the extended all-trans conformation while cation II is in a partly folded gauche+-trans-gauche - conformation. Cation II exists in the structure in two disordered gauche+-trans gauche- alternatives (A and B) located on a single inversion center and sharing common terminal C-NH~ groups. The N-C-C-C torsion angle in form IIB deviates by 15.3 (3) ° from the ideal gauche conformation (60 ° ) over the whole range of temperatures. The analogous torsion angle in form assumes a more favorable value at the lowest temperatures [-67.5 (1) ° at 30 K] but shows increasing deviations from the ideal gauche conformation as the temperature rises, the situation at room temperature being similar to that present in IIB. The amount of form decreases at a growing rate with temperature and is 80.1 (4)% at 30 K, 78.9 (4)% at 120 K and 74.0 (8)% at 275 K. The temperature dependence of the unit-cell constants suggests that a phase transition is possible slightly above 300K in agreement with the temperature variation of the IIA IIB ratio. The IIA~IIB transformation does not involve the H-bond donor and