4,2′:6′,4′′-Terpyridines: diverging and diverse building blocks in coordination polymers and metallomacrocycles

4,2′:6′,4′′-Terpyridine (4,2′:6′,4′′-tpy) is one of the less well documented isomers of the well-established bis-chelating 2,2′:6′,2′′-terpyridine. The N-donors of the outer rings in 4,2′:6′,4′′-tpy subtend an angle of 120°, leading to a description of 4,2′:6′,4′′-tpy as a divergent ligand. Because it typically binds metal ions through the outer N-donors only, 4,2′:6′,4′′-tpy is an ideal linker for combination with metal nodes (often geometrically flexible d10 ions) in coordination polymers and metallomacrocyclic complexes. The facile functionalization of terpyridines in the 4′-position allows access to a suite of 4′-X-4,2′:6′,4′′-tpy ligands in which the 4′-substituent, X, can be selected to assist in directing the metal–ligand assembly process. This overview of recent advances in the chemistry of 4,2′:6′,4′′-tpy and its 4′-substituted derivatives looks at relationships within a series of chiral polymers, competition between the formation of metallocyclic complexes versus polymers, and the use of extended aryl systems to encourage the formation of coordination polymers in which π-stacking of arene domains dominates in the assembly process. Use of metal(II) acetates is key to the formation of paddle-wheel and larger cluster nodes that direct the assembly of both predetermined and unexpected architectures.