Stability of a planar molecular conformation in a 4,4'-difluorobiphenyl crystal

Saito, Kazuya; Ataké, Tooru; Chihara, H.

doi:10.1107/s0108768187097696

Cited by 16 publications

(4 citation statements)

References 22 publications

(36 reference statements)

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“…The twisting frequency of the core may be lower in nPA than biphenyls. 15,16 As evident from Figure 2, the thermal ellipsoids of carbon atoms on the butyl group are strongly elongated, especially in the terminal methyl group. This suggests the configuration of the butyl group is disordered in this crystal.…”

Section: Resultsmentioning

confidence: 90%

Universality of Molten State of Alkyl Chain in Liquid-Crystalline Mesophases: Smectic E Phase of 6-Alkyl-2-phenylazulene

Adachi

Saitoh

Yamamura

et al. 2013

Bulletin of the Chemical Society of Japan

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Through thermodynamic, spectroscopic, and structural studies, the molten state of the alkyl chain in SmE phase, which is the liquid-crystalline mesophase closest to an ordered crystalline phase, has been established in a calamitic mesogen nPA. Combining the same conclusion for the SmE phase of another calamitic mesogen nTCB, it is concluded that the alkyl chain attached at end(s) of a rod-like core is molten in any liquid-crystalline mesophase. The thermodynamic implications are briefly discussed.Organic molecules are arranged with positional and orientational orders in crystals. When the crystal melts directly into an isotropic liquid (IL), these orders are lost simultaneously at the fusion. If these orders are lost step by step, the molecule forms a mesophase like liquid crystal (LC). Traditional classification of LCs 1 does not take into account the intramolecular degrees of freedom. Many actual mesogens have, however, intramolecular degrees of freedom in addition to those of rigid particles. It is at a glance unclear why this classification is useful in the real world. As a source of such intramolecular motional degrees of freedom, the conformational degrees of freedom of an alkyl group (or chain) is the most important because most mesogenic molecules have a molecular structure of corechain or chaincorechain, where "core" means a rigid part like a biphenyl moiety. The fact that n-alkanes, the molecules of which are just of a chain, do not exhibit liquidcrystalline mesophases implies the molecules are conformationally melted (disordered) in IL. This is really the case as evidenced by the linear increase of the entropy of fusion with a slope of ca. 10 J K ¹1 (mol of CH 2 ) ¹1, which is compatible with the threefold disorder around a CC bond. It is then natural to imagine the chain part of mesogens is also conformationally melted in their IL states. A question when the chain part melts arises, accordingly.The present authors 2,3 have previously demonstrated that the alkyl chain is already molten in smectic E (SmE) phase almost equally to those in IL in 4-alkyl-4¤-isothiocyanatobiphenyl (abbreviated as nTCB or nBT with n being the number of carbon atoms in the alkyl chain, Figure 1a) even though the SmE phase is the LC mesophase closest to a crystalline phase. 1In SmE phase, molecules are arranged in layered structure with orthorhombic symmetry. The SmE phase has no fluidity accordingly, though the layered structure is similar to the smectic A (SmA) structure. The orientational order of the molecules is partially lost in SmE phase. Namely, the molecule reorients itself around the short and the long axes, resulting in no distinction between head and tail, and front or rear faces. This is why the phase is often classified as a soft crystal (crystal E or CrE phase).1 Indeed, residual entropy determined experimentally is compatible with this structural view. 4 Despite its Figure 1. Molecular structures of (a) 4-alkyl-4¤-isothiocyanatobiphenyl (nTCB), (b) 6-alkyl-2-phenylazulene (nPA), and (c) 2-(4-alkylphenyl)indene.

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Section: Resultsmentioning

confidence: 90%

Universality of Molten State of Alkyl Chain in Liquid-Crystalline Mesophases: Smectic E Phase of 6-Alkyl-2-phenylazulene

Adachi

Saitoh

Yamamura

et al. 2013

Bulletin of the Chemical Society of Japan

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“…The structure shows that the two aryl rings of the biphenyl are coplanar, despite the steric interactions existing between the 3,5- and 3‘,5‘- hydrogen atoms of the 4,4‘-biphenyl spacer. Noteworthy, this phenomenon is observed for the two molecules in the asymmetric units in the absence of any π-stacking interactions between adjacent biphenyl moieties, well-known to stabilize such conformations in the solid state . The corresponding dication 5 [PF 6 ] 2 (Figure ) also crystallizes in the P-1 symmetry group, with one molecule in the asymmetric unit (Table ).…”

Section: Resultsmentioning

confidence: 91%

Di-organoiron Mixed Valent Complexes Featuring “(η²-dppe)(η⁵-C₅Me₅)Fe” Endgroups: Smooth Class-III to Class-II Transition Induced by Successive Insertion of 1,4-Phenylene Units in a Butadiyne-Diyl Bridge

et al. 2006

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The synthesis and study of a new redox family of symmetric dinuclear iron(II/III) complexes featuring "(eta(2)-dppe)(eta(5)-C(5)Me(5))Fe(CC)" endgroups connected by a bis(diethynyl)-4,4'-biphenyl spacer are reported. The solid-state structures were determined (X-rays) for the homovalent Fe(II)/Fe(II) and Fe(III)/Fe(III) parents. In contrast, the mixed valent (MV) complex 5[PF(6)] has a low thermodynamic stability (Kc around 10) and cannot be isolated in a pure form, but was studied in solution. According to the Robin and Day classification, it constitutes a remarkable example of well-behaved weakly coupled class-II organometallic MV compound. The photodriven metal-metal electron-transfer process takes place over ca. 16 A and corresponds to an electronic coupling of ca. 150 cm(-1) with a reorganization energy of ca. 6250 cm(-1) in dichloromethane. A similar investigation was also conducted in the near-IR range for the known and much more stable MV analogue 3[PF(6)] featuring the 1,4-phenyl unit instead of the 4,4'-biphenyl one (K(c) = 2.6 10(4)). The latter also exhibits a localized valency, but presents a very intense intervalence charge-transfer band (IVCT) with a cutoff on the low-energy side. A much stronger electronic coupling is derived (ca. 1700 cm(-1)) from the band shape for this MV complex in the frame of the two-level model. Although slowed, the electron exchange is not disrupted by insertion of an additional para-phenylene moiety into a 1,4-diethynylaryl bridge. Thus, starting from a compound with a butadiyne-diyl spacer, stepwise para-phenylene insertions in the bridge produce a smooth Class-III to Class-II transition for the corresponding MV complexes.

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“…A typical example is in p-polyphenylene crystals [23][24][25][26][27][28][29][30][31]. The molecular conformation of 1,1 0 -biphenyl changes according as the state of aggregation changes.…”

Section: Phase Transition and Polymorphism In Simple Molecular Crystalsmentioning

confidence: 99%

Application of calorimetry and thermodynamics to critical problems in materials science

Ataké¹

2009

The Journal of Chemical Thermodynamics

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Stability of a planar molecular conformation in a 4,4'-difluorobiphenyl crystal

Cited by 16 publications

References 22 publications

Universality of Molten State of Alkyl Chain in Liquid-Crystalline Mesophases: Smectic E Phase of 6-Alkyl-2-phenylazulene

Universality of Molten State of Alkyl Chain in Liquid-Crystalline Mesophases: Smectic E Phase of 6-Alkyl-2-phenylazulene

Di-organoiron Mixed Valent Complexes Featuring “(η²-dppe)(η⁵-C₅Me₅)Fe” Endgroups: Smooth Class-III to Class-II Transition Induced by Successive Insertion of 1,4-Phenylene Units in a Butadiyne-Diyl Bridge

Application of calorimetry and thermodynamics to critical problems in materials science

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Stability of a planar molecular conformation in a 4,4'-difluorobiphenyl crystal

Cited by 16 publications

References 22 publications

Universality of Molten State of Alkyl Chain in Liquid-Crystalline Mesophases: Smectic E Phase of 6-Alkyl-2-phenylazulene

Universality of Molten State of Alkyl Chain in Liquid-Crystalline Mesophases: Smectic E Phase of 6-Alkyl-2-phenylazulene

Di-organoiron Mixed Valent Complexes Featuring “(η2-dppe)(η5-C5Me5)Fe” Endgroups: Smooth Class-III to Class-II Transition Induced by Successive Insertion of 1,4-Phenylene Units in a Butadiyne-Diyl Bridge

Application of calorimetry and thermodynamics to critical problems in materials science

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Di-organoiron Mixed Valent Complexes Featuring “(η²-dppe)(η⁵-C₅Me₅)Fe” Endgroups: Smooth Class-III to Class-II Transition Induced by Successive Insertion of 1,4-Phenylene Units in a Butadiyne-Diyl Bridge