Luminescent activity of metallosupramolecular Cd(II) complexes containing dimethylterpyridine ligand

Four complexes of different Cd(II) salts with 6,6″-dimethyl-2,2′:6′,2″-terpyridine L have been synthesized of the following structural formulae: [CdL(CH₃OH)(ClO₄)₂] (1) [CdL(Cl/Br)₂] (2) [CdLCl₂] (2a) [CdL(CH₃CO₂)₂] (3). Their properties have been established through analytical and spectroscopic (ESI-MS, IR, ¹H NMR and UV–Visible absorption and emission) methods as well as by X-ray structure determinations. Quite high quantum yield values were obtained for the solution luminescence, despite the fact that presented compounds are ‘open species’ i.e. are susceptible to the effect of external environment. Titration experiments proved speciation i.e. formation of both 2:1 and 1:1 (L:Cd²⁺) species in MeCN, yet only the latter ones can be isolated in their crystalline form. In the solid state, there appears to be a correlation between the emission intensity and the stacking arrays in the lattice. There is no evidence that the methyl substituents exert a major influence upon the properties of the complexes, and it is implied however that they might also be responsible for preferential formation of 1:1 complexes in the solid state due to observed intermolecular packing lattices.