Isomerically Pure α1-Monosubstituted Tungstodiphosphates: Synthesis, Characterization and Stability in Aqueous Solutions

Abstract

Isomerically pure samples of α 1 -P 2 W 17 O 61 M were prepared, in which M represents Ca II and mainly the first-row transition metal cations: Mn II , Fe III , Co II , Ni II , Cu II , Zn II . The formula is α 1 -P 2 W 17 O 62 M for V V and Mo VI . The compounds were characterised by elemental analysis, IR, UV/Vis and 31 P NMR spectroscopy. The stability of these complexes was monitored by cyclic voltammetry and/or UV/Vis spectroscopy. All the compounds proved to be stable for at least 24 h in a pH = 3 medium, even in the presence of 0.2 M Na + , except for the precursor lacunary species itself and the Ca II -substituted derivative. In this medium, the transformation of the lacunary heteropolyanion yielded a mixture of α-[P 2 W 18 O 62 ] 6− and

Europium(III) Reduction and Speciation within a Wells−Dawson Heteropolytungstate

“…The data of part a of Figure (solid black line) for the 0.25 mM Ln-free lacunary anion shows three well-resolved processes with E 1/2 = −0.22, −0.47, and −0.81 V (identified as I, II, and III), which are attributed to W-based redox chemistry involving three successive two-electron couples . The response is essentially the same as reported beforehand for 0.25−0.5 mM solutions of K 9 Li[α-1-P 2 W 17 O 61 ] in 0.2 M Na 2 SO 4 aqueous electrolytes of pH 3.0. – Repetitive sweeps between −0.90 and +0.20 V showed reproducible behavior even though the original, colorless solution changed to light blue during the course of experimentation with different scan rates (Figure S0, Supporting Information). The blue color arises from the reductive electrochemistry and delocalization of the added electrons in the LUMOs that consist of W (α-1, belt site of Figure , left) and O character. – …”

“…Despite the availability of such structural detail, the exact speciation of Eu(III) in terms of the identity, nature, and number of different species is impossible to ascertain. The EXAFS data are consistent with a combination of P-containing species that are known decomposition products of α-1 and chelants of Eu, including [P 2 W 18 O 62 ] 6− , [α-2-P 2 W 17 O 61 ] 10− , [H 2 P 2 W 12 O 48 ] 12− , as well as Eu phosphate/(sulfate) materials. , Additional spectroscopic evidence obtained by use of optical luminescence and 31 P NMR spectroscopy was applied to disentangle the identities of the individual species produced following the complete reduction and subsequent oxidation of Eu-α-1. This combination of techniques, wherein luminescence opens a window on the speciation of Eu only, and NMR on P speciation, provides information that complements and is otherwise not available from CV and Eu XANES.…”

“…These include the original Eu-α-1 complex and the free α-1 ligand as well as one product that results from isomerization and complexation, [Eu(α-2-P 2 W 17 O 61 ) 2 ] 17− , and three products that result from fragmentation and reconstitution, [(H 2 O) n Eu(PW 11 O 39 )] 4− , [Eu(PW 11 O 39 ) 2 ] 11− , and α-[P 2 W 18 O 62 ] 6− . In view of the known chemical instabilities of the α-1 ligand, the transformations to the Eu-α-2 and plenary Wells−Dawson anions are not unexpected. It is the formation of the two lacunary Keggin complexes of Eu(III) that are unusual and possibly driven by the combined Eu- and ligand-centered reductive electrochemistry of [(H 2 O) 4 Eu(III)(α-1-P 2 W 17 O 61 )] 7− .…”

Europium(III) Reduction and Speciation within a Wells−Dawson Heteropolytungstate

“…The data of part a of Figure (solid black line) for the 0.25 mM Ln-free lacunary anion shows three well-resolved processes with E 1/2 = −0.22, −0.47, and −0.81 V (identified as I, II, and III), which are attributed to W-based redox chemistry involving three successive two-electron couples . The response is essentially the same as reported beforehand for 0.25−0.5 mM solutions of K 9 Li[α-1-P 2 W 17 O 61 ] in 0.2 M Na 2 SO 4 aqueous electrolytes of pH 3.0. – Repetitive sweeps between −0.90 and +0.20 V showed reproducible behavior even though the original, colorless solution changed to light blue during the course of experimentation with different scan rates (Figure S0, Supporting Information). The blue color arises from the reductive electrochemistry and delocalization of the added electrons in the LUMOs that consist of W (α-1, belt site of Figure , left) and O character. – …”

“…Despite the availability of such structural detail, the exact speciation of Eu(III) in terms of the identity, nature, and number of different species is impossible to ascertain. The EXAFS data are consistent with a combination of P-containing species that are known decomposition products of α-1 and chelants of Eu, including [P 2 W 18 O 62 ] 6− , [α-2-P 2 W 17 O 61 ] 10− , [H 2 P 2 W 12 O 48 ] 12− , as well as Eu phosphate/(sulfate) materials. , Additional spectroscopic evidence obtained by use of optical luminescence and 31 P NMR spectroscopy was applied to disentangle the identities of the individual species produced following the complete reduction and subsequent oxidation of Eu-α-1. This combination of techniques, wherein luminescence opens a window on the speciation of Eu only, and NMR on P speciation, provides information that complements and is otherwise not available from CV and Eu XANES.…”

“…These include the original Eu-α-1 complex and the free α-1 ligand as well as one product that results from isomerization and complexation, [Eu(α-2-P 2 W 17 O 61 ) 2 ] 17− , and three products that result from fragmentation and reconstitution, [(H 2 O) n Eu(PW 11 O 39 )] 4− , [Eu(PW 11 O 39 ) 2 ] 11− , and α-[P 2 W 18 O 62 ] 6− . In view of the known chemical instabilities of the α-1 ligand, the transformations to the Eu-α-2 and plenary Wells−Dawson anions are not unexpected. It is the formation of the two lacunary Keggin complexes of Eu(III) that are unusual and possibly driven by the combined Eu- and ligand-centered reductive electrochemistry of [(H 2 O) 4 Eu(III)(α-1-P 2 W 17 O 61 )] 7− .…”

99Tc and Re Incorporated into Metal Oxide Polyoxometalates: Oxidation State Stability Elucidated by Electrochemistry and Theory

“…These data are consistent with the formation of a dative metal–metal bond between Tc(V) and the nearest tungsten atom in the α1 lacunary POM. This structure is likely a consequence of the highly basic oxygen positioned in the α1 defect compared to the lower basicity oxygen atoms in the α2 defect. ,− ,− 183 W NMR data are consistent with this structural assignment. The 183 W NMR of Re V O-α1 suggests a similar structure.…”

Synthesis, Structure Elucidation, and Redox Properties of99Tc Complexes of Lacunary Wells−Dawson Polyoxometalates: Insights into Molecular99Tc−Metal Oxide Interactions

“…In this study, CV has been conducted in aqueous 0.1 M NaCOOCH 3 buffer solutions containing 0.5 M NaSO 4 at pH 5. The stability of both transition metal-substituted α1/α2 complexes and α1/α2 ligands with this combination of supporting electrolyte and pH has been previously demonstrated. ,, …”

Europium(III) Reduction and Speciation within a Wells−Dawson Heteropolytungstate

“…The data of part a of Figure (solid black line) for the 0.25 mM Ln-free lacunary anion shows three well-resolved processes with E 1/2 = −0.22, −0.47, and −0.81 V (identified as I, II, and III), which are attributed to W-based redox chemistry involving three successive two-electron couples . The response is essentially the same as reported beforehand for 0.25−0.5 mM solutions of K 9 Li[α-1-P 2 W 17 O 61 ] in 0.2 M Na 2 SO 4 aqueous electrolytes of pH 3.0. – Repetitive sweeps between −0.90 and +0.20 V showed reproducible behavior even though the original, colorless solution changed to light blue during the course of experimentation with different scan rates (Figure S0, Supporting Information). The blue color arises from the reductive electrochemistry and delocalization of the added electrons in the LUMOs that consist of W (α-1, belt site of Figure , left) and O character. – …”

“…Despite the availability of such structural detail, the exact speciation of Eu(III) in terms of the identity, nature, and number of different species is impossible to ascertain. The EXAFS data are consistent with a combination of P-containing species that are known decomposition products of α-1 and chelants of Eu, including [P 2 W 18 O 62 ] 6− , [α-2-P 2 W 17 O 61 ] 10− , [H 2 P 2 W 12 O 48 ] 12− , as well as Eu phosphate/(sulfate) materials. , Additional spectroscopic evidence obtained by use of optical luminescence and 31 P NMR spectroscopy was applied to disentangle the identities of the individual species produced following the complete reduction and subsequent oxidation of Eu-α-1. This combination of techniques, wherein luminescence opens a window on the speciation of Eu only, and NMR on P speciation, provides information that complements and is otherwise not available from CV and Eu XANES.…”

“…These include the original Eu-α-1 complex and the free α-1 ligand as well as one product that results from isomerization and complexation, [Eu(α-2-P 2 W 17 O 61 ) 2 ] 17− , and three products that result from fragmentation and reconstitution, [(H 2 O) n Eu(PW 11 O 39 )] 4− , [Eu(PW 11 O 39 ) 2 ] 11− , and α-[P 2 W 18 O 62 ] 6− . In view of the known chemical instabilities of the α-1 ligand, the transformations to the Eu-α-2 and plenary Wells−Dawson anions are not unexpected. It is the formation of the two lacunary Keggin complexes of Eu(III) that are unusual and possibly driven by the combined Eu- and ligand-centered reductive electrochemistry of [(H 2 O) 4 Eu(III)(α-1-P 2 W 17 O 61 )] 7− .…”

99Tc and Re Incorporated into Metal Oxide Polyoxometalates: Oxidation State Stability Elucidated by Electrochemistry and Theory

“…These data are consistent with the formation of a dative metal–metal bond between Tc(V) and the nearest tungsten atom in the α1 lacunary POM. This structure is likely a consequence of the highly basic oxygen positioned in the α1 defect compared to the lower basicity oxygen atoms in the α2 defect. ,− ,− 183 W NMR data are consistent with this structural assignment. The 183 W NMR of Re V O-α1 suggests a similar structure.…”

Synthesis, Structure Elucidation, and Redox Properties of99Tc Complexes of Lacunary Wells−Dawson Polyoxometalates: Insights into Molecular99Tc−Metal Oxide Interactions

“…In this study, CV has been conducted in aqueous 0.1 M NaCOOCH 3 buffer solutions containing 0.5 M NaSO 4 at pH 5. The stability of both transition metal-substituted α1/α2 complexes and α1/α2 ligands with this combination of supporting electrolyte and pH has been previously demonstrated. ,, …”

Europium(III) Reduction and Speciation within a Wells−Dawson Heteropolytungstate

“…The data of part a of Figure (solid black line) for the 0.25 mM Ln-free lacunary anion shows three well-resolved processes with E 1/2 = −0.22, −0.47, and −0.81 V (identified as I, II, and III), which are attributed to W-based redox chemistry involving three successive two-electron couples . The response is essentially the same as reported beforehand for 0.25−0.5 mM solutions of K 9 Li[α-1-P 2 W 17 O 61 ] in 0.2 M Na 2 SO 4 aqueous electrolytes of pH 3.0. – Repetitive sweeps between −0.90 and +0.20 V showed reproducible behavior even though the original, colorless solution changed to light blue during the course of experimentation with different scan rates (Figure S0, Supporting Information). The blue color arises from the reductive electrochemistry and delocalization of the added electrons in the LUMOs that consist of W (α-1, belt site of Figure , left) and O character. – …”

“…Despite the availability of such structural detail, the exact speciation of Eu(III) in terms of the identity, nature, and number of different species is impossible to ascertain. The EXAFS data are consistent with a combination of P-containing species that are known decomposition products of α-1 and chelants of Eu, including [P 2 W 18 O 62 ] 6− , [α-2-P 2 W 17 O 61 ] 10− , [H 2 P 2 W 12 O 48 ] 12− , as well as Eu phosphate/(sulfate) materials. , Additional spectroscopic evidence obtained by use of optical luminescence and 31 P NMR spectroscopy was applied to disentangle the identities of the individual species produced following the complete reduction and subsequent oxidation of Eu-α-1. This combination of techniques, wherein luminescence opens a window on the speciation of Eu only, and NMR on P speciation, provides information that complements and is otherwise not available from CV and Eu XANES.…”

“…These include the original Eu-α-1 complex and the free α-1 ligand as well as one product that results from isomerization and complexation, [Eu(α-2-P 2 W 17 O 61 ) 2 ] 17− , and three products that result from fragmentation and reconstitution, [(H 2 O) n Eu(PW 11 O 39 )] 4− , [Eu(PW 11 O 39 ) 2 ] 11− , and α-[P 2 W 18 O 62 ] 6− . In view of the known chemical instabilities of the α-1 ligand, the transformations to the Eu-α-2 and plenary Wells−Dawson anions are not unexpected. It is the formation of the two lacunary Keggin complexes of Eu(III) that are unusual and possibly driven by the combined Eu- and ligand-centered reductive electrochemistry of [(H 2 O) 4 Eu(III)(α-1-P 2 W 17 O 61 )] 7− .…”

99Tc and Re Incorporated into Metal Oxide Polyoxometalates: Oxidation State Stability Elucidated by Electrochemistry and Theory

“…These data are consistent with the formation of a dative metal–metal bond between Tc(V) and the nearest tungsten atom in the α1 lacunary POM. This structure is likely a consequence of the highly basic oxygen positioned in the α1 defect compared to the lower basicity oxygen atoms in the α2 defect. ,− ,− 183 W NMR data are consistent with this structural assignment. The 183 W NMR of Re V O-α1 suggests a similar structure.…”

Synthesis, Structure Elucidation, and Redox Properties of99Tc Complexes of Lacunary Wells−Dawson Polyoxometalates: Insights into Molecular99Tc−Metal Oxide Interactions

“…In this study, CV has been conducted in aqueous 0.1 M NaCOOCH 3 buffer solutions containing 0.5 M NaSO 4 at pH 5. The stability of both transition metal-substituted α1/α2 complexes and α1/α2 ligands with this combination of supporting electrolyte and pH has been previously demonstrated. ,, …”