Phase behaviour and crystal structures of 2′, 3′‐difluorinated p‐terphenyl derivatives. Issue 7 (28th June 2021)

• Record Type: Journal Article
• Authors: Gupta, Sakuntala; Das, Partha Pratim; Kula, Przemysław; Parisi, Emmanuele; Centore, Roberto
• Is Part Of: Acta crystallographica. Volume 77:Issue 7(2021)
• Page Start: 435
• Page End: 440
• Publication Date: 2021-06-28
• Subjects: difluorine -- p‐terphenyl -- disorder -- crystal structure -- terminal groups -- nematic behaviour -- POM -- DSC -- Hirshfeld -- liquid crystal; Crystallography -- Periodicals; Crystals -- Periodicals; 548.3
• DOI: 10.1107/S2053229621006367
• Languages: English
• ISSNs: 2053-2296

Abstract

Abstract : A common feature of the conformation of three difluorine derivatives of p ‐terphenyls is the noncoplanar twisted arrangement of the three rings of the p ‐terphenyl moiety. Two‐dimensional (2D) Hirshfeld fingerprint plots are consistent with H…H and C…H contacts in the crystal packing. The phase behaviour has been investigated by POM and DSC analysis. One of the compounds is mesogenic, with enantiotropic nematic behaviour. Abstract : The crystal structures of difluorine derivatives of p ‐terphenyls ( n T m ) have been determined by single‐crystal X‐ray diffraction. For the unsymmetrical substituted compounds 2′, 3′‐difluoro‐4‐methyl‐ p ‐terphenyl (1T0, C19 H14 F2 ) and 4‐ethyl‐2′, 3′‐difluoro‐4′′‐methyl‐ p ‐terphenyl (1T2, C21 H18 F2 ), the crystal structure is disordered, with molecules statistically entering the crystal in up and down orientations, with full superposition of all the atoms, except for those of the terminal groups (H/methyl for 1T0 and methyl/ethyl for 1T2). For triclinic 2′, 3′‐difluoro‐4, 4′′‐dimethyl‐ p ‐terphenyl (1T1, C20 H16 F2 ), with the space group P, the two crystallographically independent molecules have the same conformation, which is different from monoclinic 1T0 (space group C 2) and 1T2 (space group C 2/ c ). A common feature of the conformation of the three compounds is the noncoplanar twisted arrangement of the three rings of the p ‐terphenyl moiety. Two‐dimensional (2D) Hirshfeld fingerprint plots are consistent with H…H and C…H contacts in the crystal packing. For the three compounds, the phase behaviour has been investigated by POM (Petra/Osiris/Molinspiration) and differential scanning calorimetry (DSC) analysis. 1T2 is mesogenic, with enantiotropic nematic behaviour.