Directing 2D-Coordination Networks: Combined Effects of a Conformationally Flexible 3,2′:6′,3″-Terpyridine and Chain Length Variation in 4′-(4- n-Alkyloxyphenyl) Substituents

Abstract

The synthesis and characterization of 4′-(4- n-propoxyphenyl)-3,2′:6′,3″-terpyridine is described. Five 2D-coordination networks have been isolated by crystal growth at room temperature from reactions of Co(NCS) ₂ with 4′-(4- n-alkyloxyphenyl)-3,2′:6′,3″-terpyridines in which the n-alkyl group is ethyl, n-propyl, n-butyl, n-pentyl and n-hexyl in ligands 2– 6, respectively. The single-crystal structures of [{Co( 2) ₂(NCS) ₂} ^. 0.6CHCl ₃] _n , [{Co( 3) ₂(NCS) ₂} ^. 4CHCl ₃ ^. 0.25H ₂O] _n , [{Co( 4) ₂(NCS) ₂} ^. 4CHCl ₃] _n , [Co ₂( 5) ₄(NCS) ₄] _n and [Co( 6) ₂(NCS) ₂] _n have been determined, and powder X-ray diffraction has demonstrated that the single-crystal structures are representative of the bulk materials. Each compound possesses a (4,4) net with Co centres as 4-connecting nodes. For the assemblies containing 2, 3 and 4, the (4,4) net comprises two geometrically different rhombuses, and the nets pack in an ABAB... arrangement with cone-like arrangements of n-alkyloxyphenyl groups being accommodated in a similar unit in an adjacent net. An increase in the n-alkyloxy chain length has two consequences: there is a change in the conformation of the 3,2′:6′,3″-tpy metal-binding domain, and the (4,4) net comprises identical rhombuses. Similarities and differences between the assemblies with ligands 2– 6 and the previously reported [{Co( 1) ₂(NCS) ₂} ^. 3MeOH] _n and [{Co( 1) ₂(NCS) ₂} ^. 2.2CHCl ₃] _n in which 1 is 4′-(4-methoxyphenyl)-3,2′:6′,3″-terpyridine are discussed. The results demonstrate the effects of combining a variable chain length in the 4′-(4- n-alkyloxyphenyl) substituents of 3,2′:6′,3″-tpy and a conformationally flexible 3,2′:6′,3″-tpy metal-binding domain.