Ten coordination complexes obtained through a facile reaction between 2,5-dihalopyridines and copper(II) chloride (CuCl₂) are characterized using single crystal X-ray diffraction. Two series of dihalopyridine complexes based on 2-chloro-5-X-pyridine and 2-bromo-5-X-pyridine (X = F, Cl, Br and I) were prepared to analyze the C–X2/X5⋯Cl–Cu halogen bonds (XB). The influence of X2- and X5-substituents on the respective interactions was examined by comparing them to the X2/X3⋯Cl–Cu XBs found in mono-substituted halopyridine complexes, (n-X-pyridine)₂·CuCl₂ (n = 2, 3 and X = Cl, Br and I). Varying the X5-halogens in (2,5-dihalopyridine)₂·CuCl₂, the C5–X5⋯Cl–Cu XBs follow the order F5 < Cl5 < Br5 < I5 for X2 = Cl and Cl5 < Br5 < I5 for X2 = Br. The C2–X2⋯Cl–Cu XB distances did not follow any particular trends, and are slightly longer compared to corresponding distances in (2-halopyridine)₂·CuCl₂ complexes due to the competition of X2 and X5-halogen based halogen bonds. The C3–X3⋯Cl–Cu contacts in (3-halopyridine)₂·CuCl₂ have R_XB values > 1 and they cannot be considered as halogen bonds. This proves the polarization effect of X2- to X5- rather than X5- to X2-halogen, and the introduction of second halogen substituent in para-position to X5- triggers C2–X2⋯Cl–Cu and C5–X5⋯Cl–Cu XB interactions.

中文翻译：

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2,5-二卤吡啶-铜（ii）氯化物络合物中的卤素键†

通过2，5-二卤代吡啶与氯化铜（II）（CuCl ₂）的容易反应获得了十种配位络合物，使用单晶X射线衍射进行了表征。制备了两种基于2-氯-5-X-吡啶和2-溴-5-X-吡啶的二卤代吡啶配合物（X = F，Cl，Br和I）来分析C–X2 / X5⋯Cl–铜卤素键（XB）。通过将X2-和X5-取代基与单取代卤代吡啶络合物（n -X-吡啶）₂ ·CuCl ₂（n = 2，3和X = Cl，Br和I）。（2,5-二卤吡啶）₂ ·CuCl _2中的X5-卤素变化，对于X2 = Cl，C5–X5sCl–Cu XB遵循以下顺序：F5 <Cl5 <Br5 <I5，对于X2 = Br，Cl5 <Br5 <I5。C2-X2⋯Cl-Cu XB的距离没有遵循任何特定的趋势，并且由于（基于X2和X5-卤素的卤素键的竞争）（2-卤代吡啶）₂ ·CuCl ₂络合物中的相应距离而略长。所述C3-X3⋯（3卤代吡啶）CL-铜触点₂ ·的CuCl ₂有- [R _XB值> 1并且它们不能被认为是卤键。这证明了X2-X5-而不是X5- X2-卤素的极化作用，并且在X5-对位引入第二个卤素取代基会触发C2-X2XCl-Cu和C5-X5⋯Cl-Cu XB交互。