3‑Picoline Mediated Self-Assembly of M(II)–Malonate Complexes (M = Ni/Co/Mn/Mg/Zn/Cu) Assisted by Various Weak Forces Involving Lone Pair−π, π–π, and Anion···π–Hole Interactions

Five
M­(II)–malonate complexes having a common formula (C6H9N2)4[MII(C3H2O4)2(H2O)2]­(PF6)2.(H2O)2 (1–5) [where C6H9N2 = protonated 3-picoline, M­(II) = Ni/Co/Mn/Mg/Zn,
C3H4O4 = malonic acid, and PF6– = hexafluorophospahte], have been synthesized
and their crystal structures have been determined. Complexes 1–5 were found to be isostructural and
protonated 3-picoline has primarily mediated the self-assembly process.
Role of a discrete water dimer in complexes 1–5 was also studied. Weaker π–interactions have
also played crucial role in stabilizing 1D chain constructed by discrete
[MII(C3H2O4)2(H2O)2] units. An additional copper complex
namely, (C6H9N2)4[Cu­(C3H2O4)2]­(PF6)2 (6) has been synthesized from the same reagents
and was found to have a completely different structure from the others.
Structures of all the complexes are fully described and compared here.
Moreover, the lone pair−π and π–π
noncovalent interactions have been analyzed by means of DFT calculations,
mainly focusing our attention to the influence of the coordinating
metal on the strength of the interactions and the interplay between
hydrogen bonding and π-interactions. We also present here Hirshfeld
surface analysis to investigate the close intermolecular contacts.