Effect of solute-co-ordinating solvent interactions and temperature on the EPR and electronic spectra of bis(dithiophosphato)copper(II).
The self-redox reaction proceeding between two molecules of the complex bis(disubstituted-dithiophosphato)copper(II), CuII(R2-dtp)2, is studied by EPR and UV-VIS spectroscopy in DMFA, DMSO and pyridine. The effect of temperature and disulphide concentration in the solutions is also evaluated. The EPR spectra show that the g-values of CuII(R2-dtp)2 increase when it is dissolved in co-ordinating solvents, whereas the copper hyperfine splitting decreases compared to the corresponding values in non-co-ordinating solvents. Under the same conditions, a hypsochromic shift is observed in the maximal absorption at 420 nm of the electronic spectra which corresponds to the ligand-to-metal charge-transfer (LMCT) transition of the complex. The results are explained with the formation of axial or equatorial adducts between CuII(R2-dtp)2 and the co-ordinating solvents used. On the other hand, the molar absorptivity of the LMCT band and the intensity of the EPR spectrum increase strongly with the nature of the used co-ordinating solvent, the time after dissolution and the quantity of added disulphide. Both also depend on the size and shape of remote ligand substituents and they increase in the order Me < Et < i-Pr. Beer's law is not obeyed immediately after dissolution of copper bis-dithiophosphate complexes. However, after standing for 24 h in the dark, DMFA solutions exhibit linear absorption/concentration dependence with approximately 70% higher molar absorptivity. An additional increase of the LMCT band and EPR intensity is found after heating the solution up to 50 degrees C for a short time, as well as after addition of the corresponding disulphide of dithiophosphate [(RO)2P(S)S-S(S)P(RO)2] to the CuII(R2-dtp)2 solution. As a result, the molar absorptivity value at the maximum of the LMCT band of Cu[(i-PrO)2-dtp]2 increases from 7.9 x 10(3) m(-1) dm3 cm(-1) immediately after dissolution to 2.9 x 10(4) m(-1) dm3 cm(-1). In DMSO and pyridine, the intensity of both the EPR signal and LMCT band of CuII(R2-dtp)2 continuously decrease after the preparation of the solutions. A small increase is only observed immediately after the addition of the corresponding disulphide of dithiophosphate. While DMFA forms stable adducts with Cu[(i-PrO)2-dtp]2, adduct formation with DMSO and pyridine destroys the initial complex.
Yordanov
Nicola D
ND
Institute of Catalysis, Bulgarian Academy of Sciences, Sofia. ndyepr@bas.bg
Ranguelova
Kalina
K
D002627:Chemistry, Physical / Q000379:methods; D003300:Copper / Q000737:chemistry*; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D004583:Electrons; D008024:Ligands; D009942:Organometallic Compounds / Q000737:chemistry*; D010710:Phosphates / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry; D013696:Temperature; D013997:Time Factors
D004220:Disulfides; D008024:Ligands; D009942:Organometallic Compounds; D010710:Phosphates; D011725:Pyridines; D003300:Copper; C023666:pyridine; C035638:thiophosphoric acid; D004121:Dimethyl Sulfoxide