The role of non-covalent intermolecular interactions on the diversity of crystal packing in the supramolecular dihalopyridine-silver(I) nitrate complexes
Six novel 1:2 complexes of silver(I) nitrate with 2,5-, 2,6- and 3,5-dihalopyridines (halo stands for chlorine and bromine) were prepared by the reaction of an aqueous solution of AgNO3 and the corresponding pyridine derivative in water-alcohol solution. In spite of having analogous empirical formulae, they reveal intriguing structural differences, except [Ag(NO3)(2,5-Cl2py)2]n (1) and [Ag(NO3)(2,5-Br2py)2]n (4), which are isostructural. Contrary, [Ag(NO3)(3,5-Cl2py)2]2 (3) is dimeric, while its Br-analogue [Ag(NO3)(3,5-Br2py)2]n (6) is polymeric in nature, being the only complex with no halogen∙∙∙halogen interactions. Lastly, both [Ag(NO3)(2,6-Cl2py)2] (2) and [Ag(NO3)(2,6-Br2py)2] (5) consists of monomeric molecules, with dissimilar interaction patterns among units linking chains into different 3D structures. In addition, all isolated complexes were identified by the elemental analysis and characterized in solution by the multinuclear NMR spectroscopy (1H, 13C, 15N), IR and mass spectrometry. DFT calculations verified the predominant tendency of the Ag+ ions to bind two pyridine nitrogen atoms and one nitrate ion in their complexes, and confirm that their supramolecular structure is a compromise between competing weak intramolecular interactions and steric constrains.