Conformational Change of the Cation−Anion Pair of an Ionic Liquid Related to Its Low-Temperature Solid-State Phase Transitions

ABSTRACTWe report the room and low temperature crystal structures of the unsubstituted pquinquephenyl (PQP) and p-sexiphenyl (PSP), and substituted 22,45 -diphenyl-pquinquephenyl (DPQP), 22,65-diphenyl-p-septiphenyl (DPSP), and 1,2,4-triphenylbenzene (TPB) polyparaphenylene oligomers. The unsubstituted oligomers exhibit a solid state transition when cooled from room temperature to 110K, as indicated by a change in crystallographic space group. No transition is observed for the substituted oligomers other than the usual thermal contraction of the unit cell. The transition observed for the unsubstituted oligomers is interpreted in terms of a conformational change from an “averaged” planar structure to a static non-planar one. Comparisons of room temperature and low temperature crystal data are presented.

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Temperature-Dependent Phase Transitions in Two Crystalline Host–Guest Complexes Derived from Mandelic Acid

Acta Crystallographica Section B Structural Science ◽

10.1107/s0108768197010471 ◽

1998 ◽

Vol 54 (1) ◽

pp. 82-93

Author(s):

O. Hager ◽

C. Foces-Foces ◽

A. L. Llamas-Saiz ◽

E. Weber

Keyword(s):

Phase Transitions ◽

Solid State ◽

Low Temperature ◽

Inclusion Complexes ◽

Mandelic Acid ◽

Temperature Dependent ◽

Crystallographic Symmetry ◽

Crystal Packings

The supramolecular inclusion complexes of two mandelic acid-based chiral host compounds with dimethylformamide (DMF), (1) and (2), show reversible solid–solid state phase transitions upon lowering the temperature. For both inclusion complexes, the low- [(1a) and (2a) at 170 K] and the high- [(1b) at 250 and (2b) at 270 K] temperature structures were solved. (R)-1,1-Bis(4-tert-butylphenyl)-2-phenylethan-1,2-diol–dimethylformamide (1/1), C28H34O2.C3H7NO (1a), T = 170 K, monoclinic, P21, a = 14.4530 (14), b = 6.0540 (2), c = 16.1117 (14) Å, β = 105.332 (7)°, V = 1359.6 (2) Å3, Z = 2, D x = 1.162 g cm−3; (1b), T = 250 K, monoclinic, P21, a = 24.8110 (20), b = 6.0739 (2), c = 18.8645 (10) Å, β = 98.100 (6)°, V = 2814.5 (3) Å3, Z = 4, D x = 1.123 g cm−3. (R)-1,1-Bis(4-tert-butylphenyl)-2-(4-methylphenyl)ethan-1,2-diol–dimethylformamide (1/1), C29H36O2.C3H7NO (2a), T = 170 K, monoclinic, P21, a = 24.4457 (38), b = 5.9519 (6), c = 20.4609 (38) Å, β = 101.95 (1)°, V = 2912.5 (8) Å3, Z = 4, D x = 1.117 g cm−3; (2b), T = 270 K, triclinic, P1, a = 14.4172 (28), b = 6.0303 (4), c = 17.5636 (56) Å, α = 88.74 (1), β = 101.43 (2), γ = 93.13 (1)°, V = 1494.4 (6) Å3, Z = 2, D x = 1.088 g cm−3. The low-temperature forms have the higher crystallographic symmetry. In (1b) half of the DMF guests are twisted by 45.0° with respect to those in (1a). A comparative discussion of the four crystal packings is presented.

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Selected solid-state behaviour of three di-tert-butyl-substituted N-salicylideneaniline derivatives: temperature-induced phase transitions and chromic behaviour

Acta Crystallographica Section C Structural Chemistry ◽

10.1107/s2053229621008780 ◽

2021 ◽

Vol 77 (10) ◽

pp. 659-667

Author(s):

Helen E. Mason ◽

Judith A. K. Howard ◽

Hazel A. Sparkes

Keyword(s):

Phase Transition ◽

Hydrogen Bond ◽

Phase Transitions ◽

Solid State ◽

Low Temperature ◽

Schiff Bases ◽

Photochromic Properties ◽

Keto Form ◽

Single Crystal Structures ◽

State Behaviour

The synthesis, single-crystal structures and chromic behaviour of three related Schiff bases, namely, (E)-2,4-di-tert-butyl-6-{[(4-fluorophenyl)imino]methyl}phenol, C21H26FNO, 1, (E)-2,4-di-tert-butyl-6-{[(4-chlorophenyl)imino]methyl}phenol, C21H26ClNO, 2, and (E)-6-{[(4-bromophenyl)imino]methyl}-2,4-di-tert-butylphenol, C21H26BrNO, 3, are reported. Two polymorphs of 1 were obtained, which were found to have different photochromic properties. Schiff bases 2 and 3 were found to be isostructural and underwent a phase transition upon cooling which was attributed to the dynamic disorder in one of the tert-butyl groups resolving at low temperature. All of the structures were found to exist in the enol rather than the keto form based on the C—O(H) and imine C=N bond lengths, and contained an intramolecular O—H...N hydrogen bond alongside weaker intermolecular C—H...O contacts.

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