A sequence of two discontinuous phase transitions, occurring just above 125 K and 148 K, has been observed for a ferrocenyl–acetylide–gold(I) complex with triethylphosphine, structure (1), by means of a multi‐temperature single‐crystal X‐ray diffraction technique. Three distinct phases have been identified. The high‐temperature α and low‐temperature γ phases share the same space group Pbca, whereas the intermediate β phase is in the Pb2₁a subgroup of Pbca. In all phases molecules of (1) form well defined double layers, with PEt₃ groups interlocking in planes perpendicular to c. On the molecular level, both phase transitions involve almost uniquely a conformational change of triethylphosphine: a gear‐like rotation around the P—Au axis and concerted flips of the ethyl moieties. The mechanism of these transitions may be imagined as initiated by a rotation of a single PEt₃ group in a double layer (a single gear movement), followed by adjacent phosphines adjusting their conformations as a result of steric strain. The structural changes underlying phase transitions are sequential, occurring layer‐wise, the γ→β transition involving approximately every other layer in the crystal lattice, the β→α yielding a total conformation change. The sequence of phase transitions results in a noticeable contraction of the crystal cell volume.

中文翻译：

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三乙基膦作为分子齿轮-二茂铁基-乙炔化物-金（I）中的相变。

通过多温度单晶X观察到具有三乙基膦的二茂铁基-乙炔基-金（I）配合物（结构（1））出现了两个不连续的相变序列，刚好在125 K和148 K以上。射线衍射技术。已经确定了三个不同的阶段。高温α相和低温γ相具有相同的空间群Pbca，而中间的β相在Pb 2 ₁ a Pbca的亚组中。在所有相中，（1）的分子形成定义明确的双层，其中PEt _3个基团在垂直于c的平面中互锁。在分子水平上，两个相变几乎都涉及三乙基膦的构象变化：围绕P-Au轴的齿轮状旋转和乙基部分的一致翻转。可以想象这些转变的机制是由单个PEt ₃基团在双层中旋转（一次齿轮运动）引发的，随后相邻的膦因空间应变而调节其构象。相变背后的结构变化是连续的，逐层发生的，γ→β跃迁几乎涉及晶格中的每个其他层，β→α产生总构象变化。相变的顺序导致晶体晶胞体积的明显收缩。