Synthesis of two covalently linked bis(2,2′∶6′,2′′-terpyridine) (terpy) chelating ligands with different length spacers, comparison of the crystal structures of their mononuclear nickel(II) complexes, and kinetic and mechanistic studies of the reaction of one ligand with [Fe(terpy)2]2+

Abstract

Two new covalently linked bis(2,2′∶6′,2′′-terpyridine)-chelating hexadentate ligands, 1,3-bis(2,2′∶6′,2′′-terpyridyl-5-ylmethylsulfanyl)propane (L¹), and 1,4-bis(2,2′∶6′,2′′-terpyridyl-5-ylmethylsulfanyl)butane (L²), and their six-coordinate mononuclear metal complexes [ML][PF₆]₂ (M = Fe and Ni; L = L¹ and L²) have been prepared and characterised. The X-ray structures of [NiL](PF₆)₂ (L = L¹ and L²) have been compared to establish that L² has the optimum length of linker to give the least strained mononuclear complex. The marked stability of [ML]²⁺ is demonstrated by kinetic studies that show that one equivalent of L¹ is capable of substituting both 2,2′∶6′,2′′-terpyridine (terpy) ligands of [Fe(terpy)₂]²⁺ to give [FeL¹]²⁺ in a two stage kinetic process.