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

摘要

Three Co(II)-malonate complexes, namely, (C _5H _7N _2) _4[Co(C _3H _2O _4) _2(H _2O) _2](NO _3) _2 (1), (C _5H _7N _2) _4[Co(C _3H _2O _4) _2(H _2O) _2](ClO _4) _2 (2), and (C _5H _7N _2) _4[Co(C _3H _2O _4) _2(H _2O) _2](PF _6) _2 (3) [C _5H _7N _2 = protonated 2-aminopyridine, C _3H _4O _4 = malonic acid, NO _3 - = nitrate, ClO _4 - = perchlorate, PF _6 - = 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 _3 -, ClO _4 -, and PF _6 -) on the total interaction energy of the assembly is also studied.