Supramolecular assembly of zinc(II) complexes with pyridine/azo-based ligands carrying long carbon chains

Abstract

Two zinc(II) complexes, [Zn3(OAc)6(L1)2] (1) and [Zn(NO3)2(L2)2] (2), were synthesized using the ligands 2-(4-dodecyloxyphenylazo)pyridine (L1) and 2-(4- dodecyloxyphenylazo)pyrimidine (L2) (Figure). Complex 1 crystallizes in the triclinic P space group with Z = 1, with three Zn atoms coordinated by six bridging acetate ions and two chelate L1 ligands, forming a centrosymmetric trinuclear structure. Complex 2 crystallizes in the monoclinic C2/c space group as a discrete mononuclear structure with a six-coordinated Zn atom bonded to two chelate L2 ligands and two nitrate ions. The development of the crystal packing was discussed through cooperativity of dimeric motifs associated with different recognition modes. Single crystal X-ray analysis revealed that the primary structural motif in both complexes involves ribbons formed through various intermolecular interactions. Complex 1 exhibits ribbons stabilized by C−H···O and π-π interactions, while complex 2 features ribbons stabilized only by C– H···O interactions. The supramolecular ribbons in complex 1 are further linked by C−H···N and C–H···π interactions, leading to its three-dimensional packing. In contrast, the supramolecular networking of complex 2 is achieved through C–H···O, C– H···N, and π-interactions. Hydrophobic interactions between the long alkyl chains of the ligands further support the crystal structures of both complexes. The intermolecular interactions were thoroughly examined using Hirshfeld surface analysis and 2D fingerprint plots, providing insights into the packing and stability of these complexes.