The crystal structures of difluorine derivatives of p-terphenyls (nTm) have been determined by single-crystal X-ray diffraction. For the unsymmetrical substituted compounds 2′,3′-difluoro-4-methyl-p-terphenyl (1T0, C₁₉H₁₄F₂) and 4-ethyl-2′,3′-difluoro-4′′-methyl-p-terphenyl (1T2, C₂₁H₁₈F₂), 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, C₂₀H₁₆F₂), with the space group P, the two crystallographically independent molecules have the same conformation, which is different from monoclinic 1T0 (space group C2) and 1T2 (space group C2/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.

中文翻译：

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2',3'-二氟化对三联苯衍生物的相行为和晶体结构

对三联苯的二氟衍生物( n T m )的晶体结构已通过单晶 X 射线衍射确定。对于不对称取代的化合物 2',3'-difluoro-4- methyl - p - terphenyl (1T0, C ₁₉ H ₁₄ F ₂ ) 和 4-ethyl-2',3'-difluoro-4''-methyl- p -三联苯（1T2，C ₂₁ H ₁₈ F ₂)，晶体结构是无序的，分子在统计上以向上和向下的方向进入晶体，所有原子完全叠加，除了端基（1T0 的 H/甲基和 1T2 的甲基/乙基）。对于三斜 2',3'-二氟-4,4''-二甲基-对三联苯 (1T1, C ₂₀ H ₁₆ F ₂ )，空间群为P的两个晶体独立分子具有相同的构象，即不同于单斜晶系 1T0（空间群C 2）和 1T2（空间群C 2/ c）。这三种化合物构象的一个共同特征是其三个环的非共面扭曲排列。对三联苯部分。二维 (2D) Hirshfeld 指纹图与晶体堆积中的 H…H 和 C…H 接触一致。对于这三种化合物，已通过 POM（Petra/Osiris/Molinspiration）和差示扫描量热法 (DSC) 分析研究了相行为。1T2 是介晶的，具有对映向列行为。