Alkyl linker effects on the coordination topology of ditopic di(2-pyridylmethyl)amine carboxylate ligands with Zn II and Cu II : polymers vs. macrocycles

A series of ditopic ω-di(2-pyridylmethyl)amine carboxylic acid ligands incorporating a range of n -alkyl linkers ( C n COOH , n = 3–5, 7, 10 and 11) have been synthesised. Solution phase studies showed a 1 : 1 coordination stoichiometry between the ligands and M(ClO 4 ) 2 ·6H 2 O (M = Zn II or Cu II ) in all cases. The Zn II and Cu II complexes were subsequently crystallised by liquid–liquid diffusion and the solid-state structures investigated by X-ray crystallography. The crystal structures obtained are entirely consistent with the 1 : 1 metal–ligand ratio of the solution-phase adducts. However, the coordination geometries and complex topologies are dependent on the alkyl chain length of the ligand C n COOH . The Zn II and Cu II complexes of the short alkyl chain ligands ( n ≤ 5) exhibit 1D coordination polymeric structures with somewhat different conformations for {[Zn( C 3 COO )(H 2 O)](ClO 4 )·3.5H 2 O} n ( 1 ), {[Zn( C 4 COO )(H 2 O)] 4 (ClO 4 ) 4 ·1.5H 2 O} n ( 2 ), {[Zn( C 5 COO )(H 2 O)](ClO 4 )} n ( 3 ), {[Cu( C 3 COO )](ClO 4 )·MeOH} n ( 4 ), {[Cu( C 4 COO )(H 2 O)] 2 (ClO 4 ) 2 ·2H 2 O} n ( 5 ) and {[Cu( C 5 COO )(H 2 O)](ClO 4 )·2H 2 O} n ( 6 ). In contrast, the ligands with longer alkyl chains ( n ≥ 7) participate in Zn 2 L 2 metallomacrocyclic structures {[Zn( C 7 COO )(H 2 O)](ClO 4 )} 2 ( 7 ), [Zn 2 ( C 10 COO ) 2 (H 2 O) 2 ](ClO 4 ) 2 ·2H 2 O·MeOH ( 8 ) and {[Zn 2 ( C 11 COO ) 2 (H 2 O) 2 ][Zn 2 ( C 11 COO ) 2 ](ClO 4 ) 4 ·H 2 O} n ( 9 ). The formation of metallomacrocycles instead of the 1D coordination polymers is a persistent trend and, with identical crystal growth conditions and a non-coordinating anion employed, appears to be an effect of the longer alkyl chain.