Solvation of neodymium(III) perchlorate and nitrate in organic solvents as determined by spectroscopic measurements

Add time:08/12/2019    Source:sciencedirect.com

The electronic absorption, emission spectra and fluorescence lifetimes of anhydrous and diluted (0.01–0.13 M) solutions of Nd(ClO4)3 and Nd(NO3)3 in CH3CN, (CH3)2CO, DMSO, and DMF are used to investigate the solvation of the Nd(III) ion. Both the oscillator strengths and the lifetimes depend strongly upon the solvent; these latter range from 300 ns in (CH3)2CO to 485 ns in DMF, 660 ns in CH3CN, 1850 ns in DMSO, and 2300 ns in CD3CN. Upon addition of nitrate to anhydrous solutions of Nd(ClO4)3 in poorly coordinating solvents, stable, innersphere complexes of formula [Nd(NO3)n](3−n)+ form, with n = 1–5. The oscillator strength of the hypersensitive 2G52, 4G72 ← 4I92 transition increases strongly and linearly with the concentration of added nitrate. The addition of DMSO to anhydrous solution of Nd(ClO4)3 in CH3CN results in the formation of an equilibrium between nona- and deca-coordinate species [Nd(DMSO)n]3+; the average number of coordinated DMSO molecules per Nd(III) ion is estimated to be 9.7±0.8 from the lifetime data. In DMF, inner sphere nitrato complexes also form upon addition of nitrate to Nd(ClO43 solutions; equilibria take place that involve mono-, di-, and, possibly, tri-nitrato complexes, [Nd(NO3)n](3−n)+ with n = 1, 2, 3. The apparent equilibrium ratio for n = 1 is K1 = 110±30 l·mol−1.The Ωλ parameters, derived from the Judd-Ofelt theory, are calculated and discussed; in particular, Ωλ is shown to increase linearly with the number of coordinated nitrate ions in the first coordination sphere. This number is estimated to be 1.5 for Nd(NO3)3 solutions 0.02 M in DMF. The relationship between Ωλ and crystal field operators is discussed.

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