The magneto-structural correlations in Cu(25dbp)2X2 and Cu(2bp)2Br2, where 25dbp = 2,5-dibromopyridine, X = Cl or Br, and 2bp = 2-bromopyridine have been investigated. The supramolecular structures of Cu(25dbp)2X2 are based on CâBrâ¯XâCu halogen bonding interactions. The temperature dependence of the susceptibility of Cu(25dbp)2Cl2 is best represented by an antiferromagnetic chain model. This agrees with the supramolecular structure; Cu(25dbp)2Cl2 molecules form linear chains of CuâClâ¯ClâCu structural units. In contrast, the magnetic susceptibility of Cu(25dbp)2Br2 is best represented by a ferromagnetic chain model; Cu(25dbp)2Br2 molecules form a chain structure based on Cuâ¯Br2â¯BrâCu where Br2 is the bromine atom on position 2 of the 2,5-dibromopyridine ligand. The susceptibilities of Cu(2bp)2Br2 indicate that the magnetic exchange interaction is very weak, even though Cu(2bp)2Br2 forms an isostructural chain structure similar to that observed in Cu(25dbp)2Br2. This paramagnetic behavior might be due to the presence of competitive antiferromagnetic and ferromagnetic exchange pathways. The shortest CuâBrâ¯BrâCu distance is 4.5 Ã
in Cu(2bp)2Br2, where Br is the bromide ligand, whereas the shortest inter-bromide ligand distance is 5.4 Ã
in Cu(25dbp)2Br2. The two-bromide exchange pathway is known to be antiferromagnetic. This analysis is supported by DFT/B3LYP calculations. Calculations show that there is a significant spin density on the halide ligands, whereas, only a small spin density resides on Br2 (organic bromine). Also, the calculated spin density surface shows the presence of a spin end-cap along the CuâX bond, which can rationalize the two-halide exchange pathway. In addition, theoretical calculations reveal that the two-halide exchange pathway in CuX2L2 compounds is stronger than the corresponding interaction in [CuX42â] compounds.
对Cu(25dbp)2X2和Cu(2bp)2Br2中的磁-结构关系进行了研究,其中25dbp = 2,5-二
溴吡啶,X = Cl或Br,2bp =2-
溴吡啶。Cu(25dbp)2X2的超分子结构基于C–Br...X–Cu卤键相互作用。Cu(25dbp)2C
L2的磁化率随温度变化的函数最佳地符合反
铁磁链模型的结果。这与超分子结构一致;Cu(25dbp)2C
L2分子形成了Cu–Cl...Cl–Cu结构单元的线性链。相反,Cu(25dbp)2Br2的磁化率随温度变化的函数最佳地符合
铁磁链模型的结果;Cu(25dbp)2Br2分子形成了基于Cu...Br2...Br–Cu的链状结构,其中Br2是2,5-二
溴吡啶配体在2位上的
溴原子。Cu(2bp)2Br2的磁化率表明磁交换作用非常弱,尽管Cu(2bp)2Br2形成了与Cu(25dbp)2Br2所观察到的相似的等结构的链状结构。这种顺磁性行为可能是由于竞争性的反
铁磁和
铁磁交换路径的存在。Cu(2bp)2Br2中,短Cu–Br...Br–Cu距离为4.5 Å,其中Br是
溴配体,而Cu(25dbp)2Br2中,最短的
溴配体间距离为5.4 Å。已知双
溴交换路径是反
铁磁性的。这一分析得到DFT/B3LYP计算的支持。计算表明,存在显著的自旋密度在卤素
配体上,而只有很少的自旋密度位于Br2(有机
溴)上。此外,计算出的自旋密度表面显示,沿着Cu–X键存在一个自旋封端,这可以合理化双卤交换路径。此外,理论计算揭示了CuX2
L2化合物中的双卤交换路径比[CuX4$^2−}$]化合物中的相应相互作用更强。