Effect of sulfur-based substituents on the electronic properties of Re(I) dppz complexes.

A series of sulfur-substituted dppz-based ligands and their Re(I)(CO)(3)Cl complexes are reported. The sulfur-substituted ligands and complexes show interesting electronic properties atypical of dppz-type systems. Substitution of dppz with thiocyanate (SCN) groups results in behavior typical of an electron withdrawing group. However, substitution of dppz with the electron donating trithiocarbonate (S(2)CS) or deca-alkylthioether (Sdec) groups confer intraligand charge-transfer (ICT) from the S adduct to the phenazine lowest unoccupied molecular orbital (LUMO). Upon complexation of the substituted dppz ligand to Re(CO)(3)Cl this ICT red-shifts and increases in intensity. Analysis of these observations using density functional theory (DFT) calculations and resonance Raman spectroscopy reveals that these transitions are a mixture of metal-to-ligand charge-transfer (MLCT) and S --> phenazine ICT in nature. The synthesized compounds are also characterized using (1)H NMR spectroscopy, IR spectroscopy, and electrochemistry. Single-crystal X-ray analysis was performed on dppz(SCN)(2) (C(20)H(18)N(6)S(2) a = 8.780 A, b = 9.792 A, c = 10.400 A, alpha = 95.95 degrees , beta = 112.13 degrees , gamma = 95.38 degrees , triclinic, P1, Z = 2, R1 = 0.0306, wR2 = 0.0829.