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. 2023 Nov 8;28(22):7474.
doi: 10.3390/molecules28227474.

Hydrothermal Assembly, Structural Multiplicity, and Catalytic Knoevenagel Condensation Reaction of a Series of Coordination Polymers Based on a Pyridine-Tricarboxylic Acid

Xiuqi Kang  1 , Chao Ren  1 , Zhenzhong Mei  1 , Xiaoxiang Fan  1 , Jijun Xue  1 , Yongliang Shao  1 , Jinzhong Gu  1
Affiliations

Hydrothermal Assembly, Structural Multiplicity, and Catalytic Knoevenagel Condensation Reaction of a Series of Coordination Polymers Based on a Pyridine-Tricarboxylic Acid

Xiuqi Kang et al. Molecules. .

Abstract

A pyridine-tricarboxylic acid, 5-(3',5'-dicarboxylphenyl)nicotinic acid (H3dpna), was employed as a adjustable block to assemble a series of coordination polymers under hydrothermal conditions. The seven new coordination polymers were formulated as [Co(μ3-Hdpna)(μ-dpey)]n·nH2O (1), [Zn4.5(μ6-dpna)3(phen)3]n (2), [Co1.5(μ6-dpna)(2,2'-bipy)]n (3), [Zn1.5(μ6-dpna)(2,2'-bipy)]n (4), [Co3(μ3-dpna)2(4,4'-bipy)2(H2O)8]n·2nH2O (5),[Co(bpb)2(H2O)4]n[Co2(μ3-dpna)2(H2O)4]n·3nH2O (6), and [Mn1.5(μ6-dpna)(μ-dpea)]n (7), wherein 1,2-di(4-pyridyl)ethylene (dpey), 1,10-phenanthroline (phen), 2,2'-bipyridine(2,2'-bipy),4,4'-bipyridine(4,4'-bipy),1,4-bis(pyrid-4-yl)benzene (bpb), and 1,2-di(4-pyridyl)ethane (dpea) were employed as auxiliary ligands. The structural variation of polymers 1-7 spans the range from a 2D sheet (1-4, 6, and 7) to a 3D metal-organic framework (MOF, 5). Polymers 1-7 were investigated as heterogeneous catalysts in the Knoevenagel condensation reaction, leading to high condensation product yields (up to 100%) under optimized conditions. Various reaction conditions, substrate scope, and catalyst recycling were also researched. This work broadens the application of H3dpna as a versatile tricarboxylate block for the fabrication of functional coordination polymers.

Keywords: Knoevenagel condensation; catalysis; coordination polymers; crystal structures; new topology.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Structures of H3dpna and auxiliary ligands.
Scheme 2
Scheme 2
The coordination modes of Hdpna2−/dpna3−.
Figure 1
Figure 1
Structure of 1. (a) Coordination environment at Co(II) atom; hydrogen atoms are ignored except for COOH group. (b) The Co2 subunit. (c) The 2D sheet (view down the c axis). (d) Topological representation of a 3-connected network with topology (view down the c axis); 5-connected Co1 nodes (pink), centroids of 3-connected µ3-Hdpna2− nodes (gray), centroids of 2-connected µ-dpey linkers (blue).
Figure 1
Figure 1
Structure of 1. (a) Coordination environment at Co(II) atom; hydrogen atoms are ignored except for COOH group. (b) The Co2 subunit. (c) The 2D sheet (view down the c axis). (d) Topological representation of a 3-connected network with topology (view down the c axis); 5-connected Co1 nodes (pink), centroids of 3-connected µ3-Hdpna2− nodes (gray), centroids of 2-connected µ-dpey linkers (blue).
Figure 2
Figure 2
Structure of 2. (a) Coordination environment at Zn(II) centers; hydrogen atoms are ignored. (b,c) Zn3 subunits; the phen moieties are ignored. (d) The 2D sheet (view down the b axis). (e) Topological representation of a 2-nodal network with topology (view down the b axis); Zn series nodes (cyan), centroids of 6-linked µ6-dpna3− nodes (gray).
Figure 3
Figure 3
Structure of 4. (a) Coordination environment of Zn(II) atoms; hydrogen atoms are ignored. (b) The Zn3 subunit. (c) Two-dimensional metal–organic network (view down the c axis). (d) Topological representation of a 3,6-connected network with topology (view along the c axis); 3- and 6-linked Zn1/Zn2 nodes (cyan), centroids of 6-connected µ6-dpna3− nodes (gray).
Figure 4
Figure 4
Structure of 5. (a) Coordination environments at Co(II) atoms; hydrogen atoms are ignored. (b) Three-dimensional metal–organic framework (view down the c axis). (c) Topological representation of a 2,3,4-connected framework with topology (view down the c axis); 3- and 4-linked Co1/Co2 nodes (pink), centroids of 3-connected µ3-dpna3− nodes (gray), centroids of 2-connected µ-4,4′-bipy linkers (blue).
Figure 5
Figure 5
Structure of 6. (a) Coordination environment at Co(II) atoms; hydrogen atoms are ignored. (b) Two-dimensional cation metal–organic network (view down the a axis). (c) Topological representation of a 3-connected network with a fes topology (view down the a axis); 3-connected Co1 nodes (pink), centroids of 3-connected µ3-dpna3− nodes (gray).
Figure 6
Figure 6
Structure of 7. (a) Coordination environment at Mn(II) atoms; hydrogen atoms are ignored. (b) Mn3 unit. (c) Two-dimensional metal–organic network (view down the c axis). (d) Topological representation of a 2,5,6-connected network with topology (view down the c axis); Mn series nodes (light green), centroids of 6-connected µ6-dpna3− nodes (gray), centroids of 2-connected μ-dpea linkers (blue).
Scheme 3
Scheme 3
Knoevenagel condensation of benzaldehyde with malononitrile.
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