| Abstract |
The imidoylamidinate platinum(II) compounds [Pt\NH=C(R)NC(Ph)= NPh\(2)] (R= CH2Ph 2, p-ClC6H4 3, Ph 4) were prepared by the reaction of the appropriate trans-[PtCl2(RCN)(2)] with 4 equiv of the amidine PhC(=NH) NHPh giving 2-4 and 2 equivs of the salt PhC(=NH) NHPh.HCl. We also synthesized, by the double alkylation of 4 with MeOSO2CF3, complex [Pt\NH= C(Ph) N(Me) C(Ph)= NPh\(2)][CF3SO3](2) (5) which models the bis-protonated form of 4. The complexes were characterized by H-1, C-13 NMR, and IR spectroscopies, FAB-MS and by C, H, N elemental analysis. The X-ray crystallography of 4.2CH(2)Cl(2) enables the confirmation of the square planar coordination geometry of the metal center with almost planar imidoylamidine ligands, while in 5.2CHCl(3) the planarity of the metallacycles is lost and and the central N atom is sp(3)-hybridized. The imidoylamidinate complexes represent a new family of Pt(II)-based luminescent complexes and they are emissive at room temperature both in solution and in the solid state, with an emission quantum yield ranging from 3.7 x 10(-4) to 6.2 x 10(-2) in methanol solution; the emission intensity is pH-dependent, being quenched at low pH. UV-visible and luminescence spectroscopies indicate that the lowest excited state of these compounds is (MLCT)-M-3 or (IL)-I-3 with significant MLCT character, with emission lifetimes of a few mu s. A blue shift of both the absorption and emission with increasing solvent polarity and with decreasing pi-electron withdrawing properties of the ligand substituent was observed. |
