Coordination Polymers Containing M₂L₂ and M₄L₄ Metallacylces of Bis(pyridylcarboxamido)alkanes with an Odd Number of −(CH₂)– Groups as Spacers: Guest Inclusion and Networks Recognition via α Sheet

The reactions of bis­(pyridylcarboxamido)­propane (L₁, 4-pyridyl and L₂, 3-pyridyl), and bis­(pyridylcarboxamido)­pentane (L₃, 4-pyridyl and L₄, 3-pyridyl) with Cu­(I/II), Co­(II), and Cd­(II) salts in the presence of various anions resulted in one-dimensional (1D) and two-dimensional (2D) coordination polymers containing M₂L₂ and M₄L₄ metallacycles. Reactions of L₁ and L₂ with CuI afforded the formation of two different kinds of SBUs as Cu₂I₂ and Cu₄I₄, and both complexes form 1D chains, which are assembled further by α-sheet hydrogen bonding. The reactions of M­(II) salts in the absence of guest molecules lead to the formation of 1D chains containing M₂L₂-type metallacycles. These 1D chains are found to be of two types: in one type adjacent metallacycles are in plane with each other and in the second type they are nonparallel to each other. The reaction of Cu­(II) with L₁ in the presence of guest molecules such as benzonitrile or nitrobenzene leads to the formation of corrugated 2D layers containing M₄L₄ metallacycles. These 2D layers exhibit 2-fold interpenetration as well as guest inclusion simultaneously and also exhibit preferential guest-exchange dynamics. The self-complementary amide groups of the ligands assembled these coordination networks into higher dimensional architectures via amide-to-amide (α-sheet), amide-to-water, amide-to-anions, and N–H···O or O–H···O hydrogen bonds. The alkyl spacers are found to exhibit various conformations depending on the coordination network geometries, anions, and guest molecules.