Quaterphenylterpyridine: Synthesis and metal-ion complexation

A quaterphenylterpyridine ligand (qptpy) with the rodlike quaterphenyl unit attached in the 4′-position has been synthesised by a Pd-catalysed Suzuki cross-coupling reaction. A crystal structure determination on the complex [Zn(qptpy)Cl2]·dmf (dmf = dimethylformamide) has shown the ligand to be bound in the expected N3-tridentate manner to the essentially trigonal-bipyramidal dichloro metal ion, with the quaterphenyl substituents involving a twisted array of the separate phenyl groups and the shortest contacts between aromatic groups involving just the polar terpyridine head groups to give an infinite, offset face-to-face (OFF) π-stacking array. A comparison is made with the structures of the bis(ligand) complexes of Zn(ClO4)2 and Cd(ClO4)2 with the bromobiphenylterpyridine ligand (Brbptpy) synthesised as an intermediate for the formation of qptpy. A study of the absorption and emission spectra of qptpy and a range of its metal-ion complexes has shown that the ligand provides a ratiometric fluorescence response for both ZnII and CdII. Introduction of a long quaterphenyl "tail" at the 4′-position of terpyridine results in a ligand that forms a ZnII complex, which, in the solid state, retains aromatic···aromatic head-group interactions as seen in the complex of the unsubstituted ligand. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.