Analysis of coordination states for Dy(II) and Dy(III) complexes in ionic liquids by Raman spectroscopy and DFT calculation

作者：Matsumiya Masahiko^*; Kazama Ryo; Tsunashima Katsuhiko

来源：Journal of Molecular Liquids, 2016, 215: 308-315.

DOI：10.1016/j.molliq.2015.12.049

• Coordination state
• OFT calculation
• Dysprosium
• Thermodynamic property
• Raman spectroscopy

The coordination states of the divalent and trivalent dysprosium complexes in ionic liquid, triethyl-pentyl-phosphonium bis(trifluoromethylsulfonyl) amide [P-2225][TFSA] were investigated by Raman spectroscopy and DFT calculations. The concentration dependences of the deconvoluted Raman spectra were investigated for 0.23-0.45 mol kg(-1) of pure Dy(III) and the mixed sample of Dy(II)/Dy(III) = 1/3 at the molar ratio in [P-2225][TFSA]. According to the conventional analysis, the solvation number; n of Dy(II) and Dy(III) in [P-2225][TFSA] were determined to ben = 4.12 and 5.00, respectively.
Then, the thermodynamic properties such as Delta(iso)G, Delta H-iso and Delta S-iso for the isomerism of [TFSA](-) from trans- to cis-isomer in bulk and the first solvation sphere of the centered [Dy3+] cation in [P-2225][TFSA] were evaluated from the temperature dependence in the range of 298-398 K. As for the bulk condition, Delta(iso)G(bulk), Delta H-iso(bulk) and T Delta S-iso(bulk) at 298 K were - 1.06, 6.86, and 7.92 kJ mol(-1), respectively. The trans-[ITSA](-) was dominant in the enthalpy due to the positive value of Delta H-iso(bulk) and T Delta S-iso(bulk) was slightly larger than Delta H-iso(bulk), so that cis-[TFSA](-) was revealed to be an entropy-controlled in [P-2225][TFSA]. On the other hand, in the first solvation sphere of [Dy3+] cation, Delta H-iso(Dy) (-26.92 kJ mol(-1)) increased to the negative value remarkably and implied that the cis-[TFSA](-) isomers were stabilized for enthalpy. Delta H-iso(Dy) contributed to the remarkable decrease in the Delta(iso)G(Dy) and this result clearly indicated that the cis-[TFSA](-) bound to the [Dy3+] cation was preferred and the coordination state of [Dy-(III)(cis-TFSA)(5)](2-) was stable in [P-2225][TFSA].
Moreover, the optimized geometries and the bonding energies of [Dy-(II)(cis-TFSA)(4)](2-) and [Dy-(111)(cis-TFSA)(5)](2-) clusters were also investigated from DFT calculations with ADF package. The bonding energy; Delta E-b was calculated from Delta E-b = E-tot(cluster) - E-tot(DY2,3+)- nE(tot)([TEAr](-)), so that Delta E-b ([Dy-(II)(cis-TFSA)(4)](2-)) and Delta E-b([Dy-(III)(cis-TFSA)(5)](2-)) were-2135.37 and-4284.21 kJ mol(-1), respectively. This result revealed that [Dynin(cis_TEA)5](2-) cluster formed stronger coordination bonds than [Dy-(II)(cis-TFSA)(4)](2-) cluster. The average atomic charges and the bond distances of these clusters were consistent with the thermodynamic properties.

• 出版日期2016-3