Unusual Coordination Type of the Halogenated Bian Ligands in Silver(I) Complexes

This work presents the synthesis and crystal structures of novel Ag(I) complexes based on 1,2-bis[4-chlorophenyl)imino]acenaphthene (4-Cl-C₆H₄-bian) and 1,2-bis[4-iodophenyl)imino]acenaphthene (4-I-C₆H₄-bian). The interaction of AgCF₃SO₃ with 4-Cl-C₆H₄-bian led to exclusively tetrahedral complex [Ag(4-Cl-C₆H₄-bian)₂](CF₃SO₃) (1) in a 90 % yield. In contrast, the same reaction with 4-I-C₆H₄-bian led to the formation of both tetrahedral complex [Ag(4-I-C₆H₄-bian)₂](CF₃SO₃) (2) and unexpected binuclear complex [Ag₂(μ-4-I-C₆H₄-bian)₂(4-I-C₆H₄-NH₂)₂](CF₃SO₃)₂ (3), in which 4-I-C₆H₄-bian acts as a bridging ligand linking two Ag(I) ions via N- and I-donor atoms. X-ray diffraction analysis revealed an anomalously long Ag-I distance (3.0833(3) Å) in 3, resulting in duality in determining the coordination mode of the Ag(I) ion. This could be a trigonal geometry (AgN3, CN=3) or a strongly distorted trigonal-pyramidal [3+1] coordination (AgN3I, CN=4). To establish the nature of the metal-ligand interactions in complexes 1-3 and determine the coordination number of Ag(I) in complex 3, a comprehensive theoretical study (DFT calculations) was carried out using four molecular descriptors: quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), interacting quantum atoms (IQA) and second-order perturbation theory analysis of the natural bond orbital (NBO).