One- and two-dimensional polymerisation of homoleptic M(II)-complexes of 4′-(3-pyridyl)-2,2′;6′,2″-terpyridine in the solid state: A combined study by XRD, cyclic voltammetry, NMR and UV–Vis spectroscopies

Homoleptic Fe(II), Co(II), Ni(II), Cu(II) and Ru(II) complexes based on the tridentate ligand 4′-(3-pyridyl)-2,2′:6′,2″-tpy (tpy = terpyridine) have been synthesized in good yields and characterized with different techniques. Although the Fe(II) and Ru(II)-complexes exhibit diamagnetic behaviour in their solution 1H NMR spectra, the Co(II), Ni(II) and Cu(II) centres displaced the 1H resonances between 0 and 100 ppm. The electrochemical and spectroscopic properties of the complexes indicated that the pyridyl group exhibits electron-withdrawing character. Furthermore, a deep insight into the solid state packing of Co(II)- and Cu(II)-complexes, as their hexafluorophosphate (PF6) salts, reveals a two-dimensional terpyridine embrace, formed by face-to-face intermolecular π–π interactions that give rise to extended sheets in two dimensions. Modification of the PF6 anions by bulky tetraphenylborate [BPh4]− anions totally eliminates the intermolecular interactions between cations in one dimension and an extended one-dimensional polymer is formed in the other dimension.