Noncovalent-bonded 2D–3D Zn²⁺, Cd²⁺, and Cu²⁺ supramolecular coordination complexes with 2,2′-bipyridine and carboxylates: their synthesis and characterization

Abstract

The present report pertains to the synthesis and characterization of six mixed-ligand complexes of [Zn(L)(pip-)₂] (1) (L = 2,2′-bipyridine, pip =1,3-benzodioxole-5-carboxylate), [Zn(L)(mpp–)₂·H2O]·H2O (2) (mpp =2-methyl-2-phenoxypropanoate), [Cu(L)(mca^–)₂]·5H2O (3) (mca = p-methoxycinnamate), [Cd(L)( mca^–)₂·2H2O] (4), [Cd(L)2(mpp–)₂]·H2O (5) and [Cu(L)(pdp^2-)0.5Cl·H2O]2·8H2O (6) (pdp =1,4-piperazinedipropionate). The resulting complexes were characterized from EA, IR, and single-crystal XRD analysis. The TGA of all complexes were also evaluated. Compound 2 is a 2D sheet; all other complexes are 3D supramolecular assemblies. Zn and Cd have octahedral coordination geometry and Cu tetrahedral or square-pyramidal coordination.

The single-crystal XRD studies showed that 1–5 are mononuclear, while 6 is a centrosymmetric dinuclear complex. The 2,2′-bipyridines are chelating bidentate to the metal ions. The COO^– is monodentate in 2–6, while COO^– in 1 has chelating bidentate coordination. The pyridine 3(3′)-CH participated in the CH–O contact in each compound. The intricate intra- and intermolecular classical H-bonds, CH–Cl, C–H···O, CH₂···O, CH₃···O, O···π, C–π, C–H···π, CH₃–π, and π–π associations are elucidated from the X-ray crystallographic studies bringing the discrete complexes into high-dimensional ordered supramolecular structures.

GRAPHIC ABSTRACT

Keywords:

• Zn²⁺
• Cd²⁺
• Cu²⁺
• coordination compounds
• noncovalent interaction

Additional information

Funding

This work was supported by Zhejiang Provincial Science and Technology Plan Projects [grant number 2016F50058] and Zhejiang Provincial Natural Science Foundation of China [grant number LY14B010006].