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

Abstract

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.

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

“…Replacing the carboxylic acid functionality in ligand H4 by a sulfonic acid to give H13 (Figure 6) has an interesting effect on the assembly. The reaction between Na [13] and CdCl2 under hydrothermal conditions produced [Cd( 13)Cl]n which possesses a 1D-ladder structure. The compound was prepared as a model system with which to compare the photophysical behaviors of lanthanoid(III) metal analogs, and the structure is described only in the supporting information in the original work [43].…”

“…Some isomers of tpy are conformationally flexible, and this is illustrated in Scheme 4 for 3,2':6',3"-tpy for which three planar limiting conformations exist. The ligand conformation can be switched in the solid-state structure by introducing different substituents [10], and this impacts the structures of coordination polymers containing such ligands [11][12][13]. Note that while conformations A and B in Scheme 4 are divergent, conformation C is convergent and often leads to discrete molecular complexes, for example, the dizinc(II) macrocycle [14] shown in Figure 1b.…”

Adapting (4,4) Networks through Substituent Effects and Conformationally Flexible 3,2’:6’,3”-Terpyridines

“…Interestingly, these ligands only coordinate to metal ions through the outer pyridine rings. While 4,2':6',4"-tpy presents a V-shaped linker between metal centres (Scheme 1), 3,2':6',3"-tpy is conformationally flexible by virtue of inter-ring C-C bond rotation [7,[9][10][11][12]. The three limiting planar conformations of 3,2':6',3"-tpy are shown in Scheme 2.…”

“…This investigation was extended to isomeric C4-alkyloxy substituents, and revealed significant structural perturbation on going from n-butyl to branched isomers, but only subtle changes across the series rac-4-butan-2-yl, 2-methylpropyl and tert-butyl peripheral groups [21]. We have also investigated the effects of introducing different halogen-substituents in 3,2':6',3"-tpy and 4,2':6',4"-tpy ligands containing 4'-biphenyl-4-yl substituents [12,22]. The most recent of these studies focused on ligands 1-5 (Scheme 3) and revealed that the 1D-coordination polymers [Cu2(μ-OAc)4 (2)]n and [Cu2(μ-OAc)4 (3)]n are isostructural featuring inter-chain H...H and H...F interactions, respectively.…”

“…The most recent of these studies focused on ligands 1-5 (Scheme 3) and revealed that the 1D-coordination polymers [Cu2(μ-OAc)4 (2)]n and [Cu2(μ-OAc)4 (3)]n are isostructural featuring inter-chain H...H and H...F interactions, respectively. In contrast, the greater steric demands of the Me, Cl or Br substituents in [Cu2(μ-OAc)4 (1)]n, [Cu2(μ-OAc)4(4)]n and [Cu2(μ-OAc)4 (5)]n resulted in a change in the conformation of the 3,2':6',3"-tpy unit from A to B (Scheme 2) coupled with a change in inter-chain π-stacking interactions [12]. We now report how the structures of the 2D-networks formed in reactions of Co(NCS)2 with ligands 1-5 are influenced by the peripheral substituent (Me, H, F, Cl or Br).…”