Manipulating the Conformation of 3,20:60,300-Terpyridine in [Cu2(-OAc)4(3,20:60,300-tpy)]n 1D-Polymers

We report the preparation and characterization of 4'-([1,10-biphenyl]-4-yl)-3,2':6',3''-terpyridine (1), 4'-(4'-fluoro-[1,10-biphenyl]-4-yl)-3,20:60,300-terpyridine (2), 40-(40-chloro-[1,10-biphenyl]-4-yl)-3,2':6',3''-terpyridine (3), 4'-(4'-bromo-[1,10-biphenyl]-4-yl)-3,2':6',3''-terpyridine (4), and 4'-(4'-methyl-[1,10-biphenyl]-4-yl)-3,2':6',3''-terpyridine (5), and their reactions with copper(II) acetate. Single-crystal structures of the [Cu2(-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(-OAc)4(1)]n and [Cu2(-OAc)4(2)]n are isostructural, and zigzag polymer chains are present which engage in -stacking interactions between [1,10-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(-OAc)4(1)]n and [Cu2(-OAc)4(2)]n to [Cu2(-OAc)4(3)]n, [Cu2(-OAc)4(4)]n, and [Cu2(-OAc)4(5)]nnMeOH, 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 -stacking. The study underlines how the 3,2':6',3''-tpy domain can adapt to different steric demands of substituents through its conformational flexibility.