Polymeric Luminescent Zn(II) and Cd(II) Dicarboxylates Decorated by Oxime Ligands: Tuning the Dimensionality and Adsorption Capacity

Ten
Zn­(II) and Cd­(II) metal–organic materials were synthesized
and studied by the X-ray method. Among these 10 structures, two represent
binuclear clusters, and two are one-dimensional (1D) coordination
polymers, while five are laminar two-dimensional (2D) solids and one
is the three-dimensional (3D) framework. The investigation has been
aimed at rational design of coordination polymers decorated by oxime
ligands to increase the accessible adsorption area in these newly
synthesized solids. The ligands used include three aliphatic dicarboxylic
acids, HOOC-(CH2)n-COOH [n = 1, 2, 4 corresponding to malonic (H2mal),
succinic (H2suc), and adipic (H2adi) acids],
and three neutral oxime ligands [pyridine-2-aldoxime (2-pyao), pyridine-4-aldoxime
(4-pyao), and 1,2-cyclohexanedionedioxime (Niox)]. These novel hybrid
solids with the compositions [Zn2(suc)2­(2-pyao)4]­·2H2O 1, [Cd2(suc)­(2-pyao)4(H2O)2]­[BF4]2 2, [Cd­(suc)­(2-pyao)2]n 3, [Zn­(mal)­(4-pyao)­(H2O)]n 4, [Cd­(mal)­(4-pyao)­(H2O)]n 5, [Zn­(suc)­(4-pyao)]n 6, [Zn­(adi)­(4-pyao)2]n 7, {[Cd­(adi)­(4-pyao)2]·dmf}n 8, [Zn­(adi)­(Niox)]n 9, and [Cd­(adi)­(Niox)]n 10 [dmf – N,N′-dimethylformamide]
demonstrate a variable class of coordination supramolecular
architectures dictated by the distinctions in the metals’ and
oxime ligands’ coordination capacities and preferences, and
length and flexibility of the dicarboxylic linkers. The discrete aggregates 1 and 2 differ by the components’ ratio
and conformation of the bridging succinate anion; compounds 3 and 7 are 1D arrays, and compounds 4, 5, 6, 8, and 9 represent 2D layers of different topologies. Compound 10 is a 3D grid afforded by the concerted contribution of the longest
in this series adipate anion, and the bigger atomic radius Cd­(II)
vs. Zn­(II). The adsorptive properties of 7 and 9 are reported. For the laminar solid 9, the quantum
chemical simulations of the adsorption capacity are in line with the
experimental results. All new materials reveal dual green-blue wavelength
emission in the solid state.