Cobalt(ii), iron(ii), zinc(ii) and palladium(ii) complexes of di-topic 4′-{4-[bis(2-pyridyl)aminomethyl]phenyl}-2,2′:6′,2′′-terpyridine. Synthetic and X-ray structural studies

Abstract

The di-topic terpy/dpa hybrid ligand, 4′-{4-[bis(2-pyridyl)aminomethyl]phenyl}-2,2′:6′,2′′-terpyridine (L), incorporating both 2,2′:6′,2′′-terpyridine (terpy) and 2,2′-dipyridylamino domains has been synthesised. The metal complexes [CoLCl₂], [ZnLCl₂], [ZnL(CH₃CO₂)₂], [Fe(L)₂(PF₆)₂] and [Fe(L)(HL)](PF₆)_0.5(ClO₄)_2.5 have been isolated. X-ray structures of all five structures show that the respective metal ions preferentially bind to the terpy site of L, with the dpa site in the first four complexes remaining empty. In the fifth complex, which was isolated following the attempted reaction of silver perchlorate with [Fe(L)₂(PF₆)₂], one dpa site is protonated. The crystal packing of all these species is dominated by extensive π-interactions. The 5-coordinate zinc(II) and cobalt(II) complexes are isostructural and exhibit a 3D network of interactions involving π-stacking as well as CH⋯Cl and CH⋯N hydrogen bonding. Similar interactions occur in the packing of [ZnL(CH₃CO₂)₂] and [Fe(L)(HL)](PF₆)_0.5(ClO₄)_2.5 giving rise to 3D arrays. Reaction of palladium(II) with L yields a product of stoichiometry Pd₂LCl₄ for which the evidence suggests that palladium binds at both the terpy and dpa domains. Based on this result, addition of [Pd(CH₃CN)₂Cl₂] to [Fe(L)₂](PF₆) in acetonitrile yielded a heterometallic complex in which the “free” dpa sites of [Fe(L)₂](PF₆) are now occupied by palladium ions to form a heterometallic product of type [FePd₂(L)₂Cl₄](PF₆)₂·1.5CH₃CN.