# Coordination Polymers Assembled from Flexible Tricarboxylate Linkers: Hydrothermal Synthesis, Structural Diversity, and Catalytic Features

## TL;DR

Scientists created new coordination polymers using a flexible linker and tested their ability to catalyze chemical reactions efficiently.

## Contribution

A new series of coordination polymers and MOFs using a flexible tricarboxylate linker with catalytic applications is introduced.

## Key findings

- New 2D and 3D coordination polymers were synthesized using H3cpbda and metal chlorides.
- Zn-based polymers showed high catalytic activity and reusability in condensation reactions.
- Structural diversity of the polymers was confirmed through characterization.

## Abstract

The molecular design of coordination polymers (CPs) and
metal–organic
frameworks (MOFs) has attracted increasing attention in the areas
of inorganic chemistry and functional materials. In this study, a
new series of 2D CPs and 3D MOFs was hydrothermally assembled from
metal­(II) chlorides and 2,2’-((4-carboxy-1,2-phenylene)bis(oxy))­diacetic acid (H3cpbda) as a flexible
and little-explored tricarboxylate linker. Additionally, several types
of aromatic N,N-donor auxiliary
ligands were used to promote crystallization, namely, 1,10-phenanthroline
(phen), 4,4′-bipyridine (bipy), bis­(4-pyridyl)­amine (bpa),
1,2-di­(4-pyridly)­ethylene (dpey), or 1,2-di­(4-pyridly)­ethane (dpea).
The obtained products were fully characterized and identified as [M3(μ6-cpbda)2(phen)2]
n
·4nH2O (M
= Zn (1), Cd (2)), [Co3(μ5-cpbda)2(μ-bipy)2]
n
·2nH2O (3), [Zn3(μ5-cpbda)2(μ-bipy)2]
n
(4), [Zn­(μ3-cpbda)­(Hbpa)]
n
·4nH2O (5), [Zn4(μ3-cpbda)2(μ-OH)2(μ-dpey)3(H2O)2]
n
·2nH2O (6), [Co3(μ4-cpbda)2(μ-dpey)3]
n
·2nH2O (7), and [Ni3(μ4-cpbda)2(μ-dpea)3]
n
·2nH2O (8). Their
structural and topological features were also explored, allowing us
to identify a diversity of 2D and 3D coordination networks. Remarkably,
Zn-based coordination polymers 5 and 6 revealed
a high catalytic activity and reusability in the condensation reaction
between benzaldehyde and malononitrile (or ethyl cyanoacetate), leading
to almost quantitative product yields (99%) under optimized conditions.
The present work contributes to widening the family of CPs/MOFs assembled
from flexible polycarboxylate linkers and highlights a promising application
of these compounds in heterogeneous catalysis.