4'-(Pyrimidin-5-yl)- and 4'-(2-methylpyrimidin-5-yl)-4,2':6',4''-terpyridines: Selective coordination to zinc(II) through the 4,2':6',4''-terpyridine domain

The preparation and characterization of the compounds 4'-(pyrimidin-5-yl)-4,2':6',4''-terpyridine (3) and 4'-(2-methylpyrimidin-5-yl)-4,2':6',4''-terpyridine (4) are described. Preferential coordination through the terminal pyridine donors of the tpy domain is observed when 3 and 4 are treated with ZnCl2 or ZnI2. The 1-dimensional coordination polymers [{ZnCl2(3)}n], [{ZnI2(3)}n] and [{ZnI2(4)·MeOH}n] have been structurally characterized by single crystal X-ray crystallography. [{ZnI2(3)}n] is helical and crystallizes with both P- and M-helices in the lattice; the packing of P- and M-chains involves discrete tetradecker π-stacking domains involving 4,2′:6′,4″-tpy units. The introduction of the 2-methyl substituent on going from 3 to 4 has only a small effect on the structure of [{ZnI2(L)}n] (L = 3 or 4). The two coordination polymer chains assemble through face-to-face π-interactions into sheets with the pyrimidin-5-yl units projecting outwards. The presence of the 2-methyl substituents in 4 forces the sheets in [{ZnI2(4)·MeOH}n] further apart compared to those in [{ZnI2(3)}n], leading to the accommodation of MeOH molecules in cavities between the sheets.