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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

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posted on 19.03.2012, 00:00 by Prankrishna Manna, Saikat Kumar Seth, Amrita Das, Joanna Hemming, Richard Prendergast, Madeleine Helliwell, Somnath Ray Choudhury, Antonio Frontera, Subrata Mukhopadhyay
Three Co­(II)–malonate complexes, namely, (C5H7N2)4[Co­(C3H2O4)2(H2O)2]­(NO3)2 (1), (C5H7N2)4[Co­(C3H2O4)2(H2O)2]­(ClO4)2 (2), and (C5H7N2)4[Co­(C3H2O4)2(H2O)2]­(PF6)2 (3) [C5H7N2 = protonated 2-aminopyridine, C3H4O4 = malonic acid, NO3 = nitrate, ClO4 = perchlorate, PF6 = 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 13, 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 (NO3, ClO4, and PF6) on the total interaction energy of the assembly is also studied.