(NO 3) 2·(15-crown-5)·2H 2O: Three phase transitions and an intermediate modulated phase stable over a range of ca 40 K

Maxime A. Siegler, Xiang Hao, Sean Parkin, Carolyn Pratt Brock

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

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.

Original languageEnglish
Pages (from-to)486-498
Number of pages13
JournalActa Crystallographica Section B: Structural Science
Volume67
Issue number6
DOIs
StatePublished - Dec 2011

Keywords

  • commensurate approximation
  • modulated phase
  • phase transitions

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology (all)

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