Sheet, ladder or chain? Small substituents in 4′-phenyl-4,2′:6′,4″-terpyridines control dimensionality in cadmium(ii) coordination polymers

Abstract

A two-dimensional network with the sheets interlocked by face-to-face π-stacking of the phenyl substituents is formed when 4′-phenyl-4,2′:6′,4″-terpyridine combines with Cd(NO₃)₂·4H₂O. By introducing CCH, MeS or Me₂N substituents in the 4-position of the phenyl ring, the phenyl embraces are prevented. 4′-(4-Ethynyl)- and 4′-(4-methylthio)-phenyl-4,2′:6′,4″-terpyridine form 2 : 3 coordination polymers when treated with Cd(NO₃)₂·4H₂O in MeOH–CHCl₃; for 4′-(4-methylthio)-phenyl-4,2′:6′,4″-terpyridine, the assembly is shown to be solvent dependent. The 2 : 3 polymers consist of analogous one-dimensional ladders with 4,2′:6′,4″-terpyridine ligands bridging Cd(II) centres both along the edges and rungs of the ladder. Packing of ladders involves face-to-face π-stacking of pyridine rings, and a hosting of 4-ethynyl or 4-methylthio substituent in the pocket containing the non-coordinated pyridine nitrogen donor. By introducing an Me₂N substituent, the latter interaction becomes a dominant feature of the crystal packing, operating between one-dimensional polymer chains to give planar sheets; overall, a lamellar structure assembles with face-to-face π-interactions between sheets.