In 2018,Awwadi, Firas F.; Turnbull, Mark M.; Alwahsh, Manal I.; Haddad, Salim F. published 《May halogen bonding interactions compete with Cu···Cl semi-coordinate bonds? Structural, magnetic and theoretical studies of two polymorphs of trans-bis(5-bromo-2-chloro pyridine)dichlorocopper(II) and trans-bis(2,5-dichloropyridine)dichlorocopper(II)》.New Journal of Chemistry published the findings.Reference of 5-Bromo-2-chloropyridine The information in the text is summarized as follows:
Two polymorphs of Cu(25dcp)2Cl2 [Cu(25dcp)2Cl2_p1 and Cu(25dcp)2Cl2_p2] and Cu(5b2cp)2Cl2 [Cu(5b2cp)2Cl2_p1 and Cu(5b2cp)2Cl2_p2] were prepared and characterized by single crystal X-ray diffraction (25dcp = 2,5-dichloropyridine and 5b2cp = 5-bromo-2-chloropyridine). The four structures crystallize in the monoclinic crystal system: three of them (Cu(25dcp)2Cl2_p1, Cu(5b2cp)2Cl2_p2 and Cu(25dcp)2Cl2_p2) crystallize in the C2/c space group and the fourth one (Cu(5b2cp)2Cl2_p1) in the C2/m space group. Cu(5b2cp)2Cl2_p1 and Cu(25dcp)2Cl2_p1 are structurally isomorphous. The formation of two polymorphs for each complex is a result of competition between Cl···Cu semi-coordinate bonds and C-X···Cl-Cu (X = Cl or Br) halogen bonding interactions. The formation of C-X···Cl-Cu halogen bonding alone resulted in crystallization of Cu(25dcp)2Cl2_p1 and Cu(5b2cp)2Cl2_p1, whereas the formation of the Cu···Cl semi-coordinate bonds resulted in the formation of Cu(25dcp)2Cl2_p2 and Cu(5b2cp)2Cl2_p2. To our knowledge, these are the first examples in which the competition between the halogen bonding interactions and the semi-coordinate Cu···Cl resulted in the formation of different polymorphs. The calculated electrostatic potential was used to rationalize the formation of the different polymorphs. The magnetic properties of Cu(5b2cp)2Cl2_p1 were studied; it is found to obey an antiferromagnetic chain model. This magnetic behavior was rationalized using the two-halide exchange pathway. Structurally, Cu(5b2cp)2Cl2_p1 forms a chain structure based on Cu-Cl···Cl-Cu interactions. The mapped electron d. with spin d. showed the presence of a spin-d.-end-cap along the Cu-Cl bond. This spin-d.-end-cap corroborates the observed antiferromagnetic interactions. In the experiment, the researchers used 5-Bromo-2-chloropyridine(cas: 53939-30-3Reference of 5-Bromo-2-chloropyridine)
5-Bromo-2-chloropyridine(cas: 53939-30-3) belongs to pyridine. Pyridines are often used as catalysts or reagents; particular notice has been paid recently to how pyridine coordinates to metal centers enabling a wide range of valuable reactions. Reference of 5-Bromo-2-chloropyridine