Self-Assembled Zn(II) Coordination Complexes Based on Mixed V‑Shaped Asymmetric Multicarboxylate and N‑Donor Ligands

Hydrothermal
reaction between Zn­(OAc)2·2H2O and three
asymmetric semirigid V-shaped multicarboxylate ligands
H3L1–3 with the help of a 4,4'-bipyridine
(4,4'-bpy) or 1,4-bis­(imidazol-1-ylmethyl)­benzene (bix)
linker
led to the isolation of six new coordination polymers, including [Zn3(L1)2(4,4′-bpy)2]n·(H2O)2n (1), [Zn3(L2)2­(4,4′-bpy)­(H2O)2]n·(H2O)2n (2), [Zn3(L3)2­(4,4′-bpy)2­(H2O)4]n·(H2O)6n (3), [Zn3(L1)2­(bix)3]n·(H2O)7n (4), [Zn3(L2)2­(bix)3]n·(H2O)4n (5), and [Zn3(HL3)2­(bix)2]n (6), where H3L1, H3L2, H3L3 ligands
represent 3-(2-carboxyphenoxy)­phthalic acid, 4-(2-carboxyphenoxy)­phthalic
acid, 3-(4-carboxyphenoxy)­phthalic acid, respectively. Single crystal
X-ray diffraction analysis reveals a three-dimensional (3D) network
for 1 and 3–5 but a
two-dimensional (2D) structure for 2 and 6. Despite the construction from the polymetallic chains connected
by the 4,4′-bpy ligands for both compounds 1 and 2, a 3D architecture was revealed for the former species while
a 2D configuration for the latter one. Complex 3 contains
open nanotube building units composed of sole 44-numbered metallomacrocycles.
For 4, the 20-numbered metallomacrocycle subunits linked
by Zn ions give a 1D chain, which further form a 3D polymeric structure
with the help of the other cyclic-shaped subunits made from the bix
ligands and Zn ions. A 3D framework of 5 is generated
from the 2D sheets simplified as a (6,3) net bound by the bix ligands.
Compound 6 shows a 2D corrugated framework simplified
as a (4,4) net assembled by the bix ligand and dinuclear zinc unit
as node. These results seem to suggest that the diversity in the building
subunits formed in 1–6 actually originates
from the intrinsic nature of the three asymmetric V-shaped tricarboxylate
ligands together with the tunable coordination geometry and molecular
configurations of ligands by the N-donor ligand employed. In addition,
the thermal stability and luminescence properties for the series of
six complexes have also been investigated.