Electronic Studies on Coordination Metal Complexes with Xanthates Ligands: S, Ni and Mn K-edge XANES

LUCIANA C. JUNCAL; EUGENIA A. OROSCO CONDORÍ; CARLOS O. DELLA VÉDOVA; ROSANA M. ROMANO

Campinas

Otro; 25th RAU Annual Users Meeting LNLS; 2015

Laboratório Nacional de Luz Síncrotron

In this work, and as part of a general project aimed to the preparation and study of coordination complexes with potential pharmacological applications, we present the results of sulfur, nickel and manganese K-edge XANES study on a series of Ni and Mn coordination complexes with xanthate ligands and their potassium salts. Twenty three samples, with general formula (ROC(S)S-K+), (M(ROC(S)S)2) and (M(ROC(S)S)2(N-donor)1or2), with M = Ni, Mn; R = Me, Et, nPr, iPr, nBu, CF3CH2- and N-donor = py, bipy, phen, were prepared by our group in La Plata and characterized using vibrational (IR and Raman) and UV-visible spectroscopy, and also by single-crystal X-Ray diffraction analysis. The sulfur K-edge Total Ion Yield (TIY) spectra were investigated in the SXS beam-line under the proposal 16063 while the Ni and Mn K-edge XANES spectra were measured in the XAFS-1 beam-line under the proposal 17950. The XANES spectra of potassium xanthate salts (ROC(S)SK) present three resonances below the ionization energy of the 1s electrons of the sulfur atom, at 2468.3± 0.1, 2469.0 ± 0.1 y 2470.6 ± 0.2 eV, which were assigned to S1s→π*C=S and S1s→σ*C‒S transitions. In the nickel complexes, besides transitions to antibonding orbitals of the ligands, a new band around 2469.6 eV, assigned to a S1s→σ*S‒Ni transition, was observed. The Ni K-edge spectra of the studied complexes present several resonances. The pre-edge peak around 8330 eV corresponds to the transition of the nickel 1s electron to its empty 3d orbitals. The low-intensity of this resonance is in agreement with its essentially forbidden character by the dipole selection rule. The most-intense peak, assigned to a Ni1s→Ni4p transition, appears in the region of 8340 to 8350 eV and shows the most significant difference in both its intensity and the chemical shift, in dependence on the ligand alkyl sustitutent. The Mn K-edge spectra present two peaks, the pre-edge resonance around 6540 eV and the main feature close to 6550 eV.