Spectroscopic studies of Ln(III) complexes with polyoxometalates in solids, and aqueous and non‐aqueous solutions

Abstract

Chosen polyoxometalate (POM) anions and their lanthanide(III) complexes, LnPOM, have been synthesized and spectroscopically characterized in solid state, aqueous and non-aqueous solutions. POMs, such as Keggin's, Dawson's and Anderson's type,Na9EuW10O36, compositions that function as inorganic cryptands ([(Na)P5W30O110]14−-Preyssler anion, and [(Na)As4W40O140]27−), containing inorganic(Na+,K+,NH4+)or organic (tetrabutylammonium,NBu4+) counter cations were obtained and their Ln(III) complexes (sandwiched and encapsulated) studied. The synthesized compounds were identified using elemental and thermogravimetric analysis, UV-Vis spectrophotometry and FTIR spectroscopy. The complexation studies were carried out with the use Nd(III) and Er(III) optical absorption and Eu(III) luminescence spectroscopy. Luminescence characterization, including results of intensity, quantum yields and luminescence lifetimes of EuPOM complexes in aqueous, non-aqueous solutions (DMF, DMSO, acetonitryle) and solid are discussed. Based on luminescence lifetime measurements of the Eu(III) ion the hydration numbers of its sandwiched (efficient emitters) and encrypted complexes have been determined and quenching effect discussed. The Eu(III) complexes entrapped in a xerogel matrix have been studied as luminescent materials. Luminescence intensity, lifetime and quantum yield of the EuPOM materials and their photochemical stability, during continuous UV irradiation, were tested.

Synthesis and spectroscopic characterisation of chosen heteropolyanions and their Ln(III) complexes containing tetrabutylammonium counter ion

“…The Eu(III) luminescence lifetimes, measured both for solids and non-aqueous solvents (CH 3 CN, DMF), indicate that the tetrabutylammonium salt of the Preyssler Eu(III) encrypted complex has a smaller number of water molecules in the Eu((III) inner coordination sphere [34] than the potassium compound [12]. This observation confirms also a higher luminescence quantum yield measured for NBuEuP 5 W 30 in acetonitrile (1.1 × 10 −4 ) in comparison to that obtained for K 12 [EuP 5 W 30 O 110 ] in water solution (9.6×10 −5 ) [18]. These results indicate that one or two water molecules not completely encrypted in the heteropolyanion, is/are expelled from vacancy during the extraction procedure.…”

“…The highest intensity and quantum yield was obtained for NBuEuPW 11 (similarly for potassium salt of this complex in aqueous solution [14,18]) after excitation at 394 nm. However, in the DMF solution an important role bring the charge-transfer band (320-340 nm) present in mixed tungstomolibdate complexes [14][15][16].…”

“…Potassium salts of the POMs studied were synthetised and characterised as published earlier [12][13][14][15][16][17][18] according to procedures described in [19][20][21][22][23][24]. The tetrabutylammonium salts (NBu 4 POM) were obtained using the modified procedure [25] developed by Finke and co-workers [26].…”

“…In our previous study the POM anions and its europium complexes were prepared and spectroscopically (UV-Vis, FTIR, EPR and luminescence spectroscopy) characterised in solid (as potassium salt and in xerogel matrix) and in aqueous media [12][13][14][15][16][17][18]. Therefore, it is great interest to know, what occurs if the POMs anion has transferred to non-aqueous media.…”

Synthesis and sol–gel assembly of nanophosphors

“…On the other hand, stability study in temperature and under UV irradiation showed larger thermal and photochemical degradation compared with the systems with lower organic content. Similar studies have been conducted involving Eu 2 [TeMo 6 O 24 ] and [EuW 10 O 36 ] 9À anions and the resulting materials showed enhanced emission intensity and luminescence quantum yield compared with the corresponding POM in solution [51,52].…”