Abstract
The ruthenium carbonyl compounds, Ru(bpy)(CO)2X2 (X = Cl, Br or I) act as neutral halogen bond (XB) acceptors when co-crystallized with 1,4-diiodotetrafluoro-benzene (DITFB). The halogen bonding strength of the Ru-X⋅⋅⋅I halogen bonds follow the nucleophilic character of the halido ligand. The strongest halogen bond occurs between the chlorido ligand and the iodide atoms of the DITFB. All three halogen bonded complexes form polymeric assemblies in the solid state. In Ru(bpy)(CO)2Cl2⋅DITFB (1) and in Ru(bpy)(CO)2Br2⋅DITFB (2) both halido ligands are halogen bonded to only one DITFB donor. In Ru(bpy)(CO)2I2⋅DITFB (3) only one of the halido ligands is involved in halogen bonding acting as ditopic center for two DITFB donors. The polymeric structures of 1 and 2 are isomorphic wave-like single chain systems, while the iodine complexes form pairs of linear chains attached together with weak F⋅⋅⋅O≡C interactions between the closest neighbors. The stronger polarization of the iodide ligand compared to the Cl or Br ligands favors nearly linear C-I⋅⋅⋅I angles between the XB donor and the metal complex supporting the linear arrangement of the halogen bonded chain.
Highlights
Halogen bond (XB) has found to be a useful tool in crystal engineering in recent years due to its strength and directional preferences [1,2,3,4,5,6]
A molecular entity with electrophilic region on a halogen atom is defined as XB donor, while an entity with nucleophilic region, i.e., Lewis base, is defined as an XB acceptor [7]
The strength and the directionality of halogen bond are well explained by σ-hole theory and by the nature of the elements attached to the halogen atoms [8,9,10,11,12,13,14,15,16,17,18,19,20]
Summary
Halogen bond (XB) has found to be a useful tool in crystal engineering in recent years due to its strength and directional preferences [1,2,3,4,5,6]. Even if coordination to a metal center is not usually enough to generate strong σ-hole on a halido ligand, the electron density around a coordinated halogen atom, X, is polarized [28,31]. This means that the M-X···X angle in a halogen bonded M-X···X-R system is typically ranging between 90◦ and 150◦ , depending on the nature of the metal center [13,30,31]
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