Abstract
The behavior of Sr[Fe(CN)5NO]·4H2O between room temperature and 77 K has been investigated by X-ray powder diffraction (XRD), differential thermal analysis (DTA), and infrared spectroscopy (IRS). DTA puts into evidence five phase transitions—at 152.7, 174.3, 183.0, 193.0, and 199.5 K—when temperature is increased very slowly. When decreasing the temperature, XRD detects a change of space group below 153 K—from C2/m to P2/m—already reported as a result of a neutron diffraction study performed at 130 K. The P2/m space group remains at least down to 60 K. The structure at this temperature (monoclinic, space group P2/m, Z = 4, a = 19.765(21) Å, b = 7.540(5) Å, c = 8.384(1) Å, β = 98.87(1)°, V = 1236(16) Å3) has been refined to a final R factor 0.077 using 687 observed structure factors. Of the two series of IR spectra obtained when cooling the sample (first series) and when heating the previously cooled sample (second series), only a feature of the first series of spectra seems to be related with the transition observed at 153 K.
Highlights
PMR results are in very good accordance with these results
Heat amounts involved in the transitions, referred to the last (199.5 K), are Q1/Q5 = −0.82 ± 0.04, Q2/Q5 = 1.57 ± 0.08, Q3/Q5 = 1.98 ± 0.10, Q4/Q5 = 1.10 ± 0.05, Q5 = 1
X-ray powder diffraction (XRD) confirms the phase transition found by differential thermal analysis (DTA) via the change of the space group from
Summary
This work is part of a series of structural studies of solid nitroprusside hydrates directed towards establishing the relation between the (1) Laboratoire Leon Brillouin, CEN Saclay, Gif sur Yvette, France. (2) Laboratoire de Chimie et Spectroscopie Structurale Biomole-culaire, UMR7033, Universitede Paris 13,93017 Bobigny, France. (3) Laboratoire de Chimie-Physique du Solide, Ecole Centrale deParis, Chatenay-Malabry, France. (4) FAMAF, Facultad de Matematica, Astronomía y Física, Universidad Nacional de Cordoba, Cordoba, Argentina. (5) CEQUINOR (CONICET/UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina. (6) Departamento de Ciencias Basicas, Universidad Nacional deLujan, Lujan, Argentina. ∗ To whom correspondence should be addressed; e-mail: structural behavior of these compounds and the presence of weakly bonded water of crystallization molecules.[1,2]The crystal structure of Sr[Fe(CN)5NO]· 4H2O (SrNP4W) has been determined previously by X-ray diffraction at room temperature and by neutron diffraction (ND) at 300 (ND300) and 130 K (ND130) on single crystals.[2,3,4] At room temperature, the space group is C 2/m and at 130 K the space group is P2/m.2–4 Water disorder has been observed and, when going from room temperature to 130 K, the hydrogen atoms positions change as a consequence of rotation of the planes of the four independent water molecules.[4]. (4) FAMAF, Facultad de Matematica, Astronomía y Física, Universidad Nacional de Cordoba, Cordoba, Argentina. (5) CEQUINOR (CONICET/UNLP), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina. The crystal structure of Sr[Fe(CN)5NO]· 4H2O (SrNP4W) has been determined previously by X-ray diffraction at room temperature and by neutron diffraction (ND) at 300 (ND300) and 130 K (ND130) on single crystals.[2,3,4] At room temperature, the space group is C 2/m and at 130 K the space group is P2/m.2–4. Five transitions were detected by DTA at 152.7, 174.3, 183.0, 193.0, and 199.5 K when heating slowly the precooled samples (results previously advanced).[3,5] PMR reports confirmed such results.[6,7] We have performed a neutron diffraction study of SrNP4W at 60 K (ND60) to verify if new structural modifications are produced when going from 130 K to that temperature. As samples submitted to XRD suffered unavoidable dehydration, the presence of the di- and the monohydrate was detected allowing the determination of the respective space groups
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