TY - JOUR
T1 - (NO 3) 2·(15-crown-5)·2H 2O
T2 - Three phase transitions and an intermediate modulated phase stable over a range of ca 40 K
AU - Siegler, Maxime A.
AU - Hao, Xiang
AU - Parkin, Sean
AU - Brock, Carolyn Pratt
PY - 2011/12
Y1 - 2011/12
N2 - In the range 308-90 K single crystals of [Ni(H 2O) 6](NO 3) 2·(15-crown-5)·2H 2O continue to diffract well as they undergo three phase transitions. Structures have been determined at 28 different temperatures; data were collected at six more but could not be refined satisfactorily. The transitions identified structurally are in good agreement with those found by thermal analysis. Phase I (above ca 292 K; I2/m, Z = 2, Z′ = ) is disordered because the 15-crown-5 molecule is located on a 2/m site. Phase II (ca 292-248 K; P21/m, Z = 2, Z′ = ) is less disordered. Phase III (ca 248-208 K; B21, Z = 28, Z′ = 7 in a commensurate approximation) is modulated with some regions resembling phase II and the rest resembling the fully ordered phase IV (P21/c, Z = 4, Z′ = 1) that is stable below ca 208 K. The modulated structure could be determined well because crystals flash-cooled to 90 K usually retain the phase III structure. The unusual phase III may be a consequence of the differing thermal contraction of two types of alternating layers, one composed of neutral 15-crown-5 molecules and the other composed of the cations, anions and lattice water molecules, which form a hydrogen-bonded network. The two kinds of layers are linked by Oether⋯H 2Oaxial - Ni hydrogen bonds.
AB - In the range 308-90 K single crystals of [Ni(H 2O) 6](NO 3) 2·(15-crown-5)·2H 2O continue to diffract well as they undergo three phase transitions. Structures have been determined at 28 different temperatures; data were collected at six more but could not be refined satisfactorily. The transitions identified structurally are in good agreement with those found by thermal analysis. Phase I (above ca 292 K; I2/m, Z = 2, Z′ = ) is disordered because the 15-crown-5 molecule is located on a 2/m site. Phase II (ca 292-248 K; P21/m, Z = 2, Z′ = ) is less disordered. Phase III (ca 248-208 K; B21, Z = 28, Z′ = 7 in a commensurate approximation) is modulated with some regions resembling phase II and the rest resembling the fully ordered phase IV (P21/c, Z = 4, Z′ = 1) that is stable below ca 208 K. The modulated structure could be determined well because crystals flash-cooled to 90 K usually retain the phase III structure. The unusual phase III may be a consequence of the differing thermal contraction of two types of alternating layers, one composed of neutral 15-crown-5 molecules and the other composed of the cations, anions and lattice water molecules, which form a hydrogen-bonded network. The two kinds of layers are linked by Oether⋯H 2Oaxial - Ni hydrogen bonds.
KW - commensurate approximation
KW - modulated phase
KW - phase transitions
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U2 - 10.1107/S0108768111045897
DO - 10.1107/S0108768111045897
M3 - Article
C2 - 22101538
AN - SCOPUS:81855193648
SN - 0108-7681
VL - 67
SP - 486
EP - 498
JO - Acta Crystallographica Section B: Structural Science
JF - Acta Crystallographica Section B: Structural Science
IS - 6
ER -