In contrast to the broad use of terephthalic
acid as a building
block for generating metal–organic architectures, functionalized
terephthalate ligands remain significantly less investigated. In the
present study, 2-chloroterephthalic acid (CltaH2) was used
as an unexplored linker for assembling a new series of metal(II) coordination
polymers (CPs) formulated as {[Cu2(μ-Clta)(μ4
-Clta)(bipy)2]·2H2O}
n
(1), {[Cu2(μ-Clta)(μ4
-Clta)(phen)2]·2H2O}
n
(2), [Co3(μ4
-Clta)3(phen)2]
n
(3), {[Zn4(μ3-Clta)2(μ4-Clta)(μ3-OH)2(phen)2]·2H2O}
n
(4), {[Cd(μ3
-Clta)(phen)]·H2O}
n
(5), [Co2(μ-Clta)(μ4
-Clta)(μ-bpa)2]
n
(6), [Zn2(μ4
-Clta)(μ4
-biim)]
n
(7), and [Cd(μ-Clta)(H2biim)2]
n
(8). These compounds were prepared
hydrothermally from the respective metal(II) chlorides, CltaH2, and different N-donor supporting ligands acting as mediators
of crystallization (i.e., bipy, 2,2′-bipyridine; phen, 1,10-phenanthroline;
bpa, bis(4-pyridyl)amine; H2biim, 2,2′-biimidazole).
The structures of the coordination polymers 1–8 range from one-dimensional chains (5 and 8) and two-dimensional layers (1–3) to three-dimensional (3D) frameworks (4, 6, and 7); the latter also include 3D + 3D interpenetrated
examples (4, 6). Apart from different dimensionalities,
the compounds also feature distinct topologies, namely, 3,4L13 in 1 and 2, 3,4,6L12 in 3, pcu in 4, SP 1-periodic net (4,4)(0,2) in 5, sqc65 in 6, 2C1 in 8, and
a new kir1 topology in 7. Given the similarity
of the reaction conditions, the obtained wide diversity of structures
is primarily determined by the type of metal(II) node and/or crystallization
mediator. All the CPs were also screened as heterogeneous catalysts
in a model CO2 fixation reaction, namely, in the coupling
of epoxide (epichlorohydrin) with carbon dioxide, under atmospheric
pressure, and in the absence of added solvent, to produce the corresponding
cyclic carbonate. The catalytic reactions were optimized for CP 4, which revealed the best activity (up to 71% product yields),
good stability, and recyclability for up to four reaction steps. Finally,
CPs 3–8 are the first examples of
cobalt, zinc, and cadmium coordination compounds assembled from 2-chloroterephthalic
acid, thus widening its very limited application in the design of
functional metal–organic architectures.
