Anion induced formation of supramolecular associations involving lone pair-π and anion-π interactions in Co(II) malonate complexes: Experimental observations, hirshfeld surface analyses and DFT studies

Three Co(II)-malonate complexes, namely, (C H N ) [Co(C H O ) (H O) ](NO ) (1), (C H N ) [Co(C H O ) (H O) ](ClO ) (2), and (C H N ) [Co(C H O ) (H O) ](PF ) (3) [C H N = protonated 2-aminopyridine, C H O = malonic acid, NO = nitrate, ClO = perchlorate, PF = hexafluorophosphate], have been synthesized from purely aqueous media, and their crystal structures have been determined by single crystal X-ray diffraction. A thorough analysis of Hirshfeld surfaces and fingerprint plots facilitates a comparison of intermolecular interactions in 1-3, which are crucial in building supramolecular architectures. When these complexes are structurally compared with their previously reported analogous Ni(II) or Mg(II) compounds, a very interesting feature regarding the role of counteranions has emerged. This phenomenon can be best described as anion-induced formation of extended supramolecular networks of the type lone pair-π/π-π/π-anion-π/π-lone pair and lone pair-π/π-π/ π-anion involving various weak forces like lone pair-π, π-π, and anion-π interactions. The strength of these π contacts has been estimated using DFT calculations (M06/6-31+G), and the formation energy of the supramolecular networks has been also evaluated. The influence of the anion (NO , ClO , and PF ) on the total interaction energy of the assembly is also studied. © 2012 American Chemical Society.