Synthesis, X-ray crystal structure and spectroscopic characterization of the new dithiolene [Pd(Et2timdt)2] and of its adduct with molecular diiodine [Pd(Et2timdt)2]·I2·CHCl3 (Et2timdt = monoanion of 1,3-diethylimidazolidine-2,4,5-trithione)

Abstract

The first Pd dithiolene [Pd(Et₂timdt)₂] 4a belonging to the new class of metal dithiolenes deriving from the R¹₂timdt (R¹₂timdt = monoanion of 1,3-dialkylimidazolidine-2,4,5-trithione) ligand has been characterised by X-ray crystal structure determination on a single crystal [monoclinic, space group P2₁/n, a = 9.545(2), b = 5.417(2), c = 20.093(4) Å, β = 93.40(2)°, Z = 2], UV–VIS–NIR, diffuse solid state reflectance, FTIR, FT-Raman spectroscopies, solid state ¹³C NMR and cyclic voltammetry and the results have been comparatively discussed with those obtained for the analogous [Ni(Et₂timdt)₂] 4b. The UV–VIS–NIR spectrum of 4a is dominated by a very intense absorption band at 1010 nm (ε = 70 000 dm³ mol^–1 cm^–1). The NIR features of 4a and 4b have been examined on the basis of the electronic structure of their ground-state configurations, investigated by DFT calculations. The co-crystallisation of 4a with I₂ yielded the [Pd(Et₂timdt)₂]·I₂·CHCl₃ 6 adduct [monoclinic, space group C2/m, a = 21.724(9), b = 12.901(4), c = 11.004(6) Å, β = 102.83(4)°, Z = 4]. No short metal–metal interaction was observed in both 4a and 6 (Pd· · ·Pd 5.42 Å in 4a and 5.25 Å in 6), since each palladium ion is almost ‘sandwiched’ between two imidazolidine rings of parallel adjacent molecules.