Self-Assembled Zn(II) Coordination Complexes Based\non Mixed V‑Shaped Asymmetric Multicarboxylate and N‑Donor\nLigands

Abstract

Hydrothermal\nreaction between Zn­(OAc)₂·2H₂O and three\nasymmetric semirigid V-shaped multicarboxylate ligands\nH₃L^1–3 with the help of a 4,4'-bipyridine\n(4,4'-bpy) or 1,4-bis­(imidazol-1-ylmethyl)­benzene (bix)\nlinker\nled to the isolation of six new coordination polymers, including [Zn₃(L¹)₂(4,4′-bpy)₂]_<i>n</i>·(H₂O)_2<i>n</i> (<b>1</b>), [Zn₃(L²)₂­(4,4′-bpy)­(H₂O)₂]_<i>n</i>·(H₂O)_2<i>n</i> (<b>2</b>), [Zn₃(L³)₂­(4,4′-bpy)₂­(H₂O)₄]_<i>n</i>·(H₂O)_6<i>n</i> (<b>3</b>), [Zn₃(L¹)₂­(bix)₃]_<i>n</i>·(H₂O)_7<i>n</i> (<b>4</b>), [Zn₃(L²)₂­(bix)₃]_<i>n</i>·(H₂O)_4<i>n</i> (<b>5</b>), and [Zn₃(HL³)₂­(bix)₂]_<i>n</i> (<b>6</b>), where H₃L¹, H₃L², H₃L³ ligands\nrepresent 3-(2-carboxyphenoxy)­phthalic acid, 4-(2-carboxyphenoxy)­phthalic\nacid, 3-(4-carboxyphenoxy)­phthalic acid, respectively. Single crystal\nX-ray diffraction analysis reveals a three-dimensional (3D) network\nfor <b>1</b> and <b>3</b>–<b>5</b> but a\ntwo-dimensional (2D) structure for <b>2</b> and <b>6</b>. Despite the construction from the polymetallic chains connected\nby the 4,4′-bpy ligands for both compounds <b>1</b> and <b>2</b>, a 3D architecture was revealed for the former species while\na 2D configuration for the latter one. Complex <b>3</b> contains\nopen nanotube building units composed of sole 44-numbered metallomacrocycles.\nFor <b>4</b>, the 20-numbered metallomacrocycle subunits linked\nby Zn ions give a 1D chain, which further form a 3D polymeric structure\nwith the help of the other cyclic-shaped subunits made from the bix\nligands and Zn ions. A 3D framework of <b>5</b> is generated\nfrom the 2D sheets simplified as a (6,3) net bound by the bix ligands.\nCompound <b>6</b> shows a 2D corrugated framework simplified\nas a (4,4) net assembled by the bix ligand and dinuclear zinc unit\nas node. These results seem to suggest that the diversity in the building\nsubunits formed in <b>1</b>–<b>6</b> actually originates\nfrom the intrinsic nature of the three asymmetric V-shaped tricarboxylate\nligands together with the tunable coordination geometry and molecular\nconfigurations of ligands by the N-donor ligand employed. In addition,\nthe thermal stability and luminescence properties for the series of\nsix complexes have also been investigated.