Host–guest supramolecular interactions in the coordination compounds of 4,4′-Azobis(pyridine) with MnX₂ (X = NCS^–, NCNCN^– and PF₆^–): structural analyses and theoretical study

Abstract

Three new Mn(II) coordination compounds {[Mn(NCNCN)₂(azpy)]•0.5azpy}_n (1), {[Mn(NCS) ₂((azpy)(CH₃OH) ₂]•azpy}_n (2) and [Mn(azpy) ₂ (H₂O)₄][Mn(azpy)(H₂O)₅]•4PF₆•H₂O•5.5azpy (3) (where azpy = 4,4′-azobis(pyridine)) have been synthesized by self-assembly of the primary ligands, dicyanamide, thiocyanate and hexafluorophosphate, respectively, together with azpy as the secondary spacer. All three complexes were characterized by elemental analyses, IR spectroscopy, thermal analyses, and single crystal X-ray crystallography. The structural analyses reveal that complex 1 forms a two-dimensional (2D) grid sheet motif. These sheets assemble to form a microporous framework that incorporates coordination-free azpy by host–guest π•••π and C–H•••N hydrogen bonding interactions. Complex 2 features azpy bridged one-dimensional (1D) chains of centrosymmetric [Mn(NCS) ₂(CH ₃OH)2] units which form a 2D porous sheet via a CH₃•••π; supramolecular interaction. A guest azpy molecule is incorporated within the pores by strong H-bonding interactions. Complex 3 affords a 0-D motif with two monomeric Mn (II) units in the asymmetric unit. There exist π•••π, anion•••π and strong hydrogen bonding interactions between the azpy, water and the anions. Density Functional Theory (DFT) calculations, at the M06/6-31+G* level of theory are used to characterize a great variety of interactions that explicitly show the importance of host–guest supramolecular interactions for the stabilization of coordination compounds and creation of the fascinating three-dimensional (3D) architecture of the title compounds.