The preparation of 2⁴-functionalized 1²,2²:2⁶,3²-terpyridines (4′-functionalized 3,2:6′,3″-terpyridines) by the reaction of three 4-alkoxybenzaldehydes with 3-acetylpyridine and ammonia was investigated; under identical reaction conditions, two (R =ⁿC₄H₉, C₂H₅) gave the expected products whereas a third (R = ⁿC₃H₇) gave only a cyclohexanol derivative derived from the condensation of three molecules of 3-acetylpyridine with two of 4-(n-propoxy)benzaldehyde. A comprehensive survey of “unexpected” products from reactions of ArCOCH₃ derivatives with aromatic aldehydes is presented. Three different types of alternative product are identified.

Five coordination polymers formed from combinations of copper(II) acetate and 4′-(4-alkyloxyphenyl)-3,2′:6′,3″-terpyridines with methoxy (1), n-butoxy (2), n-pentyloxy (3) and n-heptyloxy (4) substituents are reported. Reaction of 1 with Cu(OAc)₂∙H₂O leads to the 1D-polymer [Cu₂(μ-OAc)₄(1)]_n in which {Cu₂(μ-OAc)₄} paddle-wheel units are connected by ligands 1, or [{Cu₄(μ₃-OH)₂(μ-OAc)₂(μ₃-OAc)₂(AcO-κO)₂(1)₂}·2MeOH]_n in which centrosymmetric tetranuclear clusters link pairs of ligands 1 to give a double-stranded 1D-polymer. Layering solutions of Cu(OAc)₂∙H₂O (in MeOH) over 2, 3 or 4 (in CHCl₃) leads to the assembly of the 1D-polymers [2{Cu₂(μ-OAc)₄(2)}·1.25MeOH]_n, [Cu₂(μ-OAc)₄(3)]_n and [{Cu₂(μ-OAc)₄(4)}·0.2CHCl₃]_n. In all compounds, the 3,2′:6′,3″-tpy unit coordinates only through the outer pyridine rings, but the conformation of the 3,2′:6′,3″-tpy responds to changes in the length of the alkyloxy tails leading to changes in the conformation of the polymer backbone and in the packing of the chains in the crystal lattice in the chains featuring {Cu₂(μ-OAc)₄} paddle-wheel linkers.

The synthesis and characterization of 4′-(4-methoxyphenyl)-3,2′:6′,3″-terpyridine (2) (IUPAC PIN 2⁴-(4-methoxyphenyl)-1²,2²:2⁶,3²-terpyridine) are described, and its coordination behaviour with cobalt(II) thiocyanate has been investigated. In a series of experiments, crystals were grown at room temperature by layering a MeOH solution of Co(NCS)₂ over a CHCl₃ solution of 2 using 1:1, 1:2 or 2:1 molar ratios of metal salt-to-ligand. Crystals harvested within 2–3 weeks proved to be the 1D-coordination polymer [Co(2)(NCS)₂(MeOH)₂]_n and powder X-ray diffraction (PXRD) confirmed that the crystals selected for single-crystal X-ray diffraction were representative of the bulk samples. Longer crystallization times with a Co(NCS)₂ to 2 molar ratio of 1:1 yielded crystals of [Co(2)(NCS)₂(MeOH)₂]_n (1D-chain) and the pseudopolymorphs [{Co(2)₂(NCS)₂}·3MeOH]_n and [{Co(2)₂(NCS)₂}·2.2CHCl₃]_n ((4,4)-nets), each type of crystal originating from a different zone in the crystallization tube. PXRD for this last experiment confirmed that the dominant product in the bulk sample was the 1D-coordination polymer.

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.