Optically “silent” neptunium(V)-nitrate complex in ionic liquid

Effect of hydration of a room temperature ionic liquid on the cation–cation interaction of UO22+ and NpO2+ ions

“…A similar shift in the Np( v ) f–f transition with water content in a RTIL was also reported recently by Dong et al , 41 who reported a peak at 976 nm for water-saturated C 4 mim.NTf 2 , which falls well in line with the present observation. The authors 41 have also shown Np( v ) f–f transition at 968.9 nm at 250 mg L −1 water, which is down-shifted compared to the peak at 971 nm observed in the present case for 5000 mg L −1 water. This observation suggests that the peak position of the Np( v ) f–f transition gets blue-shifted with the decreasing hydration level of C 4 mim.NTf 2 .…”

“…13 The vis-NIR spectrum of Np( v ) in wet RTIL shows a prominent peak at 976 nm, characteristic of the ion whereas for dry RTIL an additional peak at 1002 nm was seen along with the 971 peak, which can be attributed to its complexation with different ligands. 50–52 Dong et al , 41 have also observed few peaks in the Np( v ) vis-NIR spectrum in dry C 4 mim.NTf 2 and assigned their occurrence to the Np–hydroxo or carbonato complexes. 41 Though one would be tempted to conclude accordingly, our studies for CCI interactions between Np( v ) and U( vi ) in dry RTIL and wet RTIL contradict these peak assignments.…”

“…Although the Np( v ) f–f transition peak position and the associated ε value are known for the aqueous media, only one report is available on the complexation of Np( v ) with nitrate in RTIL. 41 Our earlier studies for CCI of Np( v ) with the other actinides such as U( vi ) 12 or Th( iv ) 11 suggested that the CCI of Np( v ) with other actinides, such as U( vi ) was weak and electrostatic in nature and hence, should be very much affected by the medium. Xian et al have also shown that the strength of the CCI between Np( v ) and U( vi ) increases with increasing ionic strength of the aqueous medium.…”

“…[24][25][26][27][28][29][30] The liquid-liquid extraction of Ln/An using RTILs as a solvent 21,26,29,31 and/or direct dissolution of Ln/An oxides in the RTIL 25,28,[32][33][34][35][36] has gained popularity in the recent past. 31,35,37 Although there are several reports available on the U(VI) ion stability, complexation and speciation in RTILs, [38][39][40] there is no report on the Np(v) speciation in a hydrophobic RTIL except one recently published by Dong et al 41 The unusual stability of the different oxidation states of Np in a hydrophilic RTIL (namely Hbet.NTf 2 ) was reported by Long et al 42 A hydrolysis-stable complex of Np(IV), i.e., [BuMeIm] 2 [NpCl 6 ] (where BuMeIm + is 1-n-butyl-3-methylimidazolium) in a hydrophobic RTIL 43 was reported by Nikitenko et al 43 Although the Np(V) f-f transition peak position and the associated e value are known for the aqueous media, only one report is available on the complexation of Np(V) with nitrate in RTIL. 41 Our earlier studies for CCI of Np(V) with the other actinides such as U(VI) 12 or Th(IV) 11 suggested that the CCI of Np(V) with other actinides, such as U(VI) was weak and electrostatic in nature and hence, should be very much affected by the medium.…”

“…24–30 The liquid–liquid extraction of Ln/An using RTILs as a solvent 21,26,29,31 and/or direct dissolution of Ln/An oxides in the RTIL 25,28,32–36 has gained popularity in the recent past. 31,35,37 Although there are several reports available on the U( vi ) ion stability, complexation and speciation in RTILs, 38–40 there is no report on the Np(v) speciation in a hydrophobic RTIL except one recently published by Dong et al 41 The unusual stability of the different oxidation states of Np in a hydrophilic RTIL (namely Hbet.NTf 2 ) was reported by Long et al 42 A hydrolysis-stable complex of Np( iv ), i.e. , [BuMeIm] 2 [NpCl 6 ] (where BuMeIm + is 1- n -butyl-3-methylimidazolium) in a hydrophobic RTIL 43 was reported by Nikitenko et al .…”