Abstract

A new polymorph of the β-modification of N,N′-di(pyridin-2-yl)formamidine that is more thermodynamically stable than the known α-modification is obtained. The crystal of β-modification contains hydrogen bonded molecular dimers with a skewed geometry. Therefore, the space group is not centrosymmetric – P4₂. This geometry is a result of the molecular E-syn,syn conformation in crystals of the β-phase, which differs from the E-anti,syn conformation in the α-phase. The number of crystallographically non-equivalent molecules (8) in the β-modification is unusually large for organic compounds. The structure of the packing is analyzed, and it is shown that the centers of dimers follow the sites of a distorted body-centered cubic pseudo-lattice (А_т ≈ 10 Å, α_т = 90°) with a 16 times decreased unit cell volume. Reasons for symmetry violations causing modulations are considered.

中文翻译：

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二吡啶基取代的甲脒的构象二元论

摘要

获得了 N,N'-二（吡啶-2-基）甲脒的 β-改性的新多晶型物，它比已知的 α-改性在热力学上更稳定。β-改性晶体包含具有倾斜几何形状的氢键分子二聚体。因此，空间群不是中心对称的——P 4 ₂。这种几何结构是β 相晶体中分子E-syn、syn构象的结果，它不同于E-anti、synα相的构象。对于有机化合物，β-变体中晶体学上非等价分子 (8) 的数量异常大。填料的结构进行了分析，其结果表明，二聚物的中心跟随的位点的失真的体心立方准晶格（А _т 听，说：10埃，α _т  = 90°）用16倍降低单位单元体积。考虑了导致调制的对称违规的原因。