Molecular Accordion: Vapoluminescence and Molecular Flexibility in the Orange and Green Luminescent Crystals of the Dimer, Au₂(μ-bis-(diphenylphosphino)ethane)₂Br₂

Solutions containing the components Au+, dppe (dppe is bis(diphenylphosphino)ethane), and Br– in a 1:1:1 ratio can produce three different types of crystals: type A, orange luminescent solvates of the dimer Au2(dppe)2Br2 (Au2(μ-dppe)2Br2·2(OSMe2), Au2(μ-dppe)2Br2·2(OCMe2), Au2(μ-dppe)2Br2·2(CH2Cl2), Au2(μ-dppe)2Br2·2(HC(O)NMe2)); type B, green luminescent solvates of the same dimer (Au2(μ-dppe)2Br2·(NCMe) and Au2(μ-dppe)2Br2·0.5(C4H10O)); and type C, orange luminescent solvates of a polymer ({Au(μ-dppe)Br}n·0.5(C4H10O) and {Au(μ-dppe)Br}n·(CH2Cl2)). Some crystals of types A are solvoluminescent. Exposure of type A crystals of Au2(μ-dppe)2Br2·2(OCMe2) or Au2(μ-dppe)2Br2·2(CH2Cl2) to air or vacuum results in the loss of the orange luminescence and the formation of new green luminescent crystals. Subsequent exposure of these crystals to acetone or dichloromethane vapor results in the reformation of crystals of type A. The dimeric complexes in crystals of types A and B are all centrosymmetric and share a common ring conformation. Within these dimers, the coordination geometry of each gold center is planar with a P2Br donor set. In other respects, the Au2(μ-dppe)2Br2 molecule is remarkably flexible and behaves as a molecular accordion, whose dimensions depend upon the solvate content of a particular crystalline phase. In particular, the dimer Au2(μ-dppe)2Br2 is able to accommodate Au···Au separations that range from 3.8479(3) to 3.0943(2) Å, and these variations along with alterations in the Au–Br distances and in the P–Au–P angles are the likely causes of the differences in the luminescence properties of these crystals.将含有金(I)阳离子（Au+）、双(二苯基膦)乙烷（dppe, bis(diphenylphosphino)ethane）与溴阴离子（Br–）按1:1:1摩尔比混合的溶液，可生成三类不同的晶体：A类为二聚体Au₂(μ-dppe)₂Br₂的橙色发光溶剂化物，具体包括Au₂(μ-dppe)₂Br₂·2(OSMe₂)、Au₂(μ-dppe)₂Br₂·2(OCMe₂)、Au₂(μ-dppe)₂Br₂·2(CH₂Cl₂)与Au₂(μ-dppe)₂Br₂·2(HC(O)NMe₂)；B类为同一二聚体的绿色发光溶剂化物，包括Au₂(μ-dppe)₂Br₂·(NCMe)与Au₂(μ-dppe)₂Br₂·0.5(C₄H₁₀O)；C类为聚合物{Au(μ-dppe)Br}ₙ的橙色发光溶剂化物，包括{Au(μ-dppe)Br}ₙ·0.5(C₄H₁₀O)与{Au(μ-dppe)Br}ₙ·(CH₂Cl₂)。部分A类晶体具有溶剂致发光变色特性。将Au₂(μ-dppe)₂Br₂·2(OCMe₂)或Au₂(μ-dppe)₂Br₂·2(CH₂Cl₂)的A类晶体暴露于空气或真空环境中，会失去橙色发光并转化为新型绿色发光晶体。将所得晶体重新置于丙酮或二氯甲烷蒸气中，则可恢复为A类晶体。A、B两类晶体中的二聚体配合物均为中心对称结构，且共享共同的环构象。在这些二聚体中，每个金中心的配位几何为平面构型，配体给体组为P₂Br。除此之外，Au₂(μ-dppe)₂Br₂分子具有显著的结构柔性，可作为分子手风琴（molecular accordion），其尺寸取决于特定晶相中的溶剂化物含量。具体而言，该二聚体可容纳的金-金（Au···Au）间距范围为3.8479(3)至3.0943(2)埃（Å），这类间距变化，连同Au–Br键长与P–Au–P键角的改变，大概率是导致不同晶体发光性能差异的原因。