Syntheses, structures and luminescence for zinc coordination polymers based on a multifunctional 4′-(3-carboxyphenyl)- 3,2′:6′,3″-terpyridine ligand

A Tail Does Not Always Make a Difference: Assembly of cds Nets from Co(NCS)2 and 1,4-bis(n-Alkyloxy)-2,5-bis(3,2':6',3″-terpyridin-4'-yl)benzene Ligands

The consistent assembly of a (6⁵.8) cds net is observed in reactions of cobalt(II) thiocyanate with 1,4-bis(n-alkyloxy)-2,5-bis(3,2′:6′,3″-terpyridin-4′-yl)benzene ligands in which the n-alkyloxy substituents are n-propyl (ligand 3), n-butyl (4), n-pentyl (5), n-hexyl (6), n-heptyl (7), and n-octyl (8). Crystals were grown by layering a methanol solution of Co(NCS)₂ over a 1,2-dichlorobenzene solution of each ligand. The choice of crystallization solvents is critical in directing the assembly of the cds net. Single-crystal structures of [Co(NCS)₂(3)]_n^.3.5nC₆H₄Cl₂, [Co(NCS)₂(4)]_n^.5.5nC₆H₄Cl₂, [Co(NCS)₂(5)]_n^.4nC₆H₄Cl₂, [Co(NCS)₂(6)]_n^.3.8nC₆H₄Cl₂, [Co(NCS)₂(7)]_n^.3.1nC₆H₄Cl₂, and [Co(NCS)₂(8)]_n^.1.6nC₆H₄Cl₂^.2nMeOH (C₆H₄Cl₂ = 1,2-dichlorobenzene) are presented and compared. The n-alkyloxy chains exhibit close to extended conformations and are accommodated in cavities in the lattice without perturbation of the coordination framework.

Multitopic 3,2′:6′,3′′-terpyridine ligands as 4-connecting nodes in two-dimensional 4,4-networks

The tetratopic 1,4-bis(2-phenylethoxy)-2,5-bis(3,2′:6′,3′′-terpyridin-4′-yl)benzene (1) and 1,4-bis(3-phenylpropoxy)-2,5-bis(3,2′:6′,3′′-terpyridin-4′-yl)benzene (2) ligands have been prepared and fully characterised. Combination of ligand 1 or 2 and [M(hfacac)₂]·xH₂O (M = Cu, x = 1; M = Zn, x = 2) under conditions of crystal growth by layering led to the formation of [Cu₂(hfacac)₄(1)]_n·3.6n(1,2-Cl₂C₆H₄)·2nCHCl₃, [Zn₂(hfacac)₄(1)]_n·nMeC₆H₅·1.8nCHCl₃, [Cu₂(hfacac)₄(2)]_n·nMeC₆H₅·2nH₂O, [Cu₂(hfacac)₄(2)]_n·2.8nC₆H₅Cl and [Cu₂(hfacac)₄(2)]_n·2n(1,2-Cl₂C₆H₄)·0.4nCHCl₃·0.5nH₂O. For each compound, single-crystal X-ray analysis revealed the assembly of a planar (4,4)-net in which the tetratopic ligands 1 or 2 define the nodes. The metal centres link two different bis(3,2′:6′,3′′-tpy) ligands via the outer pyridine rings; whereas copper(ii) has N-donors in a trans-arrangement, zinc(ii) has them in cis. This difference between the copper(ii) and zinc(ii) coordination polymers modifies the architecture of the assembly without changing the underlying (4,4)-network.

Ligands containing two 3,2′:6′,3′′-terpyridine metal-binding domains act as 4-connecting nodes in 2D (4,4)-networks; subtle structural changes occur on coordination to Cu(ii) or Zn(ii).

Isomers of Terpyridine as Ligands in Coordination Polymers and Networks Containing Zinc(II) and Cadmium(II)

The use of divergent 4,2′:6′,4″- and 3,2′:6′,3″-terpyridine ligands as linkers and/or nodes in extended coordination assemblies has gained in popularity over the last decade. However, there is also a range of coordination polymers which feature 2,2′:6′,2″-terpyridine metal-binding domains. Of the remaining 45 isomers of terpyridine, few have been utilized in extended coordination arrays. Here, we provide an overview of coordination polymers and networks containing isomers of terpyridine and either zinc(II) and cadmium(II). Although the motivation for investigations of many of these systems is their luminescent behavior, we have chosen to focus mainly on structural details, and we assess to what extent assemblies are reproducible. We also consider cases where there is structural evidence for competitive product formation. A point that emerges is the lack of systematic investigations.

Terpyridine-Based 3D Metal-Organic-Frameworks: A Structure-Property Correlation

Design, synthesis, and applications of metal-organic frameworks (MOFs) are among the most salient fields of research in modern inorganic and materials chemistry. As the structure and physical properties of MOFs are mostly dependent on the organic linkers or ligands, the choice of ligand system is of utmost importance in the design of MOFs. One such crucial organic linker/ligand is terpyridine (tpy), which can adopt various coordination modes to generate an enormous number of metal-organic frameworks. These frameworks generally carry physicochemical characteristics induced by the π-electron-rich (basically N-electron-rich moiety) terpyridines. In this minireview, the construction of 3D MOFs associated with symmetrical terpyridines is discussed. These ligands can be easily derivatized at the lateral phenyl (4'-phenyl) position and incorporate additional organic functionalities. These functionalities lead to some different binding modes and form higher dimensional (3D) frameworks. Therefore, these 3D MOFs can carry multiple features along with the characteristics of terpyridines. Some properties of these MOFs, like photophysical, chemical selectivity, photocatalytic degradation, proton conductivity, and magnetism, etc. have also been discussed and correlated with their frameworks.

Manipulating the Conformation of 3,2′:6′,3″-Terpyridine in [Cu2(μ-OAc)4(3,2′:6′,3″-tpy)]n 1D-Polymers

We report the preparation and characterization of 4′-([1,1′-biphenyl]-4-yl)-3,2′:6′,3″-terpyridine (1), 4′-(4′-fluoro-[1,1′-biphenyl]-4-yl)-3,2′:6′,3″-terpyridine (2), 4′-(4′-chloro-[1,1′-biphenyl]-4-yl)-3,2′:6′,3″-terpyridine (3), 4′-(4′-bromo-[1,1′-biphenyl]-4-yl)-3,2′:6′,3″-terpyridine (4), and 4′-(4′-methyl-[1,1′-biphenyl]-4-yl)-3,2′:6′,3″-terpyridine (5), and their reactions with copper(II) acetate. Single-crystal structures of the [Cu2(μ-OAc)4L]n 1D-coordination polymers with L = 1–5 have been determined, and powder X-ray diffraction confirms that the single crystal structures are representative of the bulk samples. [Cu2(μ-OAc)4(1)]n and [Cu2(μ-OAc)4(2)]n are isostructural, and zigzag polymer chains are present which engage in π-stacking interactions between [1,1′-biphenyl]pyridine units. 1D-chains nest into one another to give 2D-sheets; replacing the peripheral H in 1 by an F substituent in 2 has no effect on the solid-state structure, indicating that bifurcated contacts (H...H for 1 or H...F for 2) are only secondary packing interactions. Upon going from [Cu2(μ-OAc)4(1)]n and [Cu2(μ-OAc)4(2)]n to [Cu2(μ-OAc)4(3)]n, [Cu2(μ-OAc)4(4)]n, and [Cu2(μ-OAc)4(5)]n·nMeOH, the increased steric demands of the Cl, Br, or Me substituent induces a switch in the conformation of the 3,2′:6′,3″-tpy metal-binding domain, and a concomitant change in dominant packing interactions to py–py and py–biphenyl face-to-face π-stacking. The study underlines how the 3,2′:6′,3″-tpy domain can adapt to different steric demands of substituents through its conformational flexibility.

Sometimes the Same, Sometimes Different: Understanding Self-Assembly Algorithms in Coordination Networks

The syntheses and characterizations of three new ligands containing two 4,2':6',4″-tpy or two 3,2':6',3″-tpy metal-binding domains are reported. The ligands possess different alkyloxy functionalities attached to the central phenylene spacer: n-pentyloxy in 3, 4-phenyl-n-butoxy in 4, benzyloxy in 5. Crystal growth under ambient conditions has led to the formation of {[Co(NCS)₂(3)]·0.8C₆H₄Cl₂}n and {[Co(NCS)₂(4)]·1.6H₂O·1.2C₆H₄Cl₂}n, with structures confirmed by single crystal X-ray diffraction. Both the cobalt(II) center and ligand 3 or 4 act as 4-connecting nodes and both {[Co(NCS)₂(3)]·0.8C₆H₄Cl₂}n and {[Co(NCS)₂(4)]·1.6H₂O·1.2C₆H₄Cl₂}n possess a 3D cds net despite the fact that 3 and 4 contain two 4,2':6',4″-tpy and two 3,2':6',3″-tpy units, respectively. Taken in conjunction with previously reported data, the results indicate that the role of the alkyloxy substituent is more significant than the choice of 4,2':6',4″- or 3,2':6',3″-tpy isomer in determining the assembly of a particular 3D net. The combination of Co(NCS)₂ with 5 resulted in the formation of the discrete molecular complex [Co(NCS)₂(MeOH)₂(5)₂]·2CHCl₃·2MeOH in which 5 acts as a monodentate ligand. The pendant phenyls and both coordinated and non-coordinated 4,2':6',4″-tpy units are involved in efficient π-stacking interactions.

A multifunctional Ni(ii) coordination polymer: synthesis, crystal structure and applications as a luminescent sensor, electrochemical probe, and photocatalyst

A new Ni(ii) complex containing 2,5-dichloroterephthalate and rigid bis(imidazole) ligands, which manifests multifunctional properties, has been synthesized and characterized.