Pendyala Srinivas

First reported synthesis of ammonium hexafluorodioxouranate(VI), (NH4)4[UO2F6]

Abstract Bis(acetylacetonato)dioxouranium(VI) dihydrate, UO2(C5H7O2)2·2H2O, reacts with NH4F in the presence of an excess of acetylacetone and a trace of water to produce (NH4)4[UO2F6] in high yield. The results of chemical analyses, molar conductance, IR and laser Raman spectroscopic studies have been used for characterisation of the compound.

Fluoride-assisted stabilisation of amino acid complexes of vanadium Synthesis and characterisation

Abstract Fluoride amino acid complexes of vanadium(IV) of the type A[VOF 2 L(H 2 O)] (A = Naor NH 4 , L = cysteinate) and A[VOF 3 L(H 2 O)] (A = NH 4 for L = alanine and A = Na, NH 4 or K for L = serine) have been synthesised. The compounds have been characterised by chemical analyses, chemical determination of the oxidation state of vanadium, solution electrical conductance and magnetic susceptibility measurements, ESR, IR and electronic spectral studies. The vibrational spectra of the complexes indicate coordination of the amino acids through their carboxylate group to the metal centre. Also, the sulphydryl functionality provides an additional coordination site in cysteine-containing complexes. Fluoride appears to act as a stabilising ligand which helps in the solid-state isolation of the complexes.

Synthesis and spectroscopic characterization of mixed-fluoro complexes of UO22+ containing amino acids, acetylacetonate or acetate as the co-ligands and the first report on the heptafluoroxioxouranate(VI) complex [UO2F7]5−

Abstract The synthesis of mixed-ligand fluoro complexes of UO 2 2+ of the types A 3 [UO 2 (GlyH) 2 F 5 ] · 3H 2 O [A = K (1) or NH 4 + (2)], K 3 [UO 2 (AlanH) 2 F 5 · 2H 2 O (3), (NH 4 ) 5 [UO 2 (CysH) 2 F 5 ]·2H 2 O (4), [UO 2 (acac)F(H 2 O) 2 ] · 3H 2 O (6), K 2 [UO 2 (acac)F 3 ] (8) and [UO 2 (CH 3 COO)F(H 2 O) 2 ] (9) (GlyH = glycine, AlanH = alanine, CysH − = cysteinate and acac − = acetylacetonate) is described. The complexes have been characterized by a combination of chemical analyses, solution conductance measurements and spectroscopic studies. Vibrational spectroscopy has been used for their structural assessment. Laser Raman spectrum could be recorded only for K 2 [UO 2 (acac)F 3 ] (8), while an extensive fluorescence foiled such attempts on the other complexes. Each of the three amino acid co-ligands acts in a unidentate manner, being coordinated to UO 2 2+ through the caroxylate oxygen atom. While glycine and alanine occur in the zwitter-ionic form, cysteine seems to be present as a uninegative ligand. The reaction of [UO 2 (acac)F(H 2 O) 2 ]·3H 2 O (6) with aqueous HF produced [UO 2 F 2 ] · 3H 2 O (7). Treatment of K 3 [UO 2 (GlyH) 2 F 5 ] · 3H 2 O (1) with water afforded the hitherto unreported potassium heptafluorodioxouranate(VI) dihydrate, K 5 [UO 2 F 7 · 2H 2 O (5), in a high yield with satisfactory ana measurement (590 Ω −1 cm 2 mil −1 ). IR and laser Raman spectra provide clear evidence for the presence of trans -linked OUO and coordinated fluoride. The solution Raman spectrum of 5 is similar to that of its solid indicating that the structure in aqueous solution is the same as the solid. Scanning electron microscopy has been used to ascertain its homogeneity and crystalline nature.

Complex fluorouranates (VI). Synthesis characterization and structural assessment of new mixed-fluoro complexes of UO22+ containing phosphate, nitrate or hydrazine as the co-ligands

Abstract New mixed-fluoro complexes of UO 2 2+ of the types A 2 [UO 2 (PO 4 )F(H 2 O) 3 ]·3H 2 O [A = K ( 1 ), Na ( 2 ) or NH 4 + ( 3 )], A 2 [UO 2 (NO 3 ) 3 F] · 3H 2 O [A = K ( 4 ), Na ( 5 ) or NH 4 + ( 6 ) and [UO 2 (N 2 H 4 ) 2 F 2 ] · 2H 2 O ( 7 ) have been synthesized. The compounds have been characterized by analyses, electrical conductance measurements and electronic, IR and laser Raman (IR) spectroscopic studies. The occurrence of trans -linked (OUO), coordinated fluoride and bidentate co-ligands are the common features of complexes 1 – 7 . Typically, the scanning electron micrographs of 2 and 7 provide evidence for their crystallinity and homogeneity. The laser Raman spectra of the aqueous solutions of the systems 1 – 6 and the solid complexes 1 – 7 were recorded separately. While for the reaction solutions (cf. 1 – 6 ) the symmetric stretching frequency of OUO was observed at ca 840 cm −1 , the band was found to occur at ca 900 cm −1 for the solids 1 – 7 . This has been interpreted in terms of the decrease in the hydration number of the coordination shell of UO 2 2+ of the solid complexes.

Direct synthesis of anhydrous alkali-metal tetrafluorodioxouranates(VI), A2[UO2F4], and the first synthesis of alkali-metal diaquatetrafluorodioxouranate(VI) monohydrates, A2[UO2F4(H2O)2]·H2O (A = Na, K or NH4)

Anhydrous alkali-metal tetrafluorodioxouranates(VI), A2[UO2F4](A = Na, K or NH4), have been synthesised directly from the reaction of [UO2(O2)]·2H2O with aqueous HF and alkali-metal fluorides AF (A = Na, K or NH4). The yellow product obtained by addition of an alkali to an aqueous solution of [UO2(NO3)2]·6H2O yielded, with aqueous HF and alkali-metal carbonates, the alkali-metal diaquatetrafluorodioxouranate(VI) monohydrates, A2[UO2F4(H2O)2]·H2O (A = Na, K or NH4). The compounds are crystalline. Infrared and laser Raman spectroscopic investigations provided the basis of their structural assessment. The solution electrical conductance (ca. 242 Ω–1 cm2 mol–1) attests to their 2 : 1 ionic nature and stability in aqueous solution. Pyrolysis of [NH4]2[UO2F4(H2O)2]·H2O at 120 °C followed by deuteriation and IR spectroscopy of the product provided evidence for the occurrence of a molecule of lattice water and two aqua ligands.

Occurrence of a manganese(III) intermediate in the [MnO4]––SO2 redox reaction

Evidence for a manganese(III) intermediate, previously implicated in the [MnO4]––SO2 electron-transfer process, has been obtained by conducting the reaction in the presence of F–. A combination of in situ EPR and electronic absorption spectroscopies was used to follow the reaction course and physico-chemical techniques were used to ascertain the identity of the isolated manganese(III) products. The evidence suggests that in the presence of F– manganese(VII) is directly reduced to manganese(III) and thence to manganese(II).

Reactivity investigations of some chosen peroxo-vanadium(V), manganese(III) and chromium(VI) compounds

An interpretative account of the results of reactions in aqueous medium of a highly peroxygenated vanadium(V) complex, K [V(O23]·3H2O, with different organic and inorganic substrates is presented. The reactions were monitored by solution EPR spectroscopy and isolation of products at different stages of the reactions. Redox reactions between diperoxide, K[VO(O2)2(H2O)] and VOSO4 were conducted. The results of the investigation suggest that secondary oxygen exchange-reaction occurs which not only depends on but also utilises the intermediates in the primary reaction during diperoxovanadate-dependent oxidation of VOSO4.In an interesting reactiontris(acetylacetonato)-manganese(III), Mn(acac)3, on being reacted with a hydrogen peroxide adduct, KF·H2O2, and bpy and phen afforded crystalline [Mn(acac)2(bpy)] and [Mn(acac)2(phen)], respectively. The X-ray structural analysis of [Mn(acac)2(phen)] showed that the compound crystallised in orthorhombic space groupPbcn. The structure consists of a pseudooctahedral Mn(II) ion being bound to two acac−(C5H5O2−) and a phen ligand with the molecule lying on two-fold axis.Reactivity profiles of two new chromium(VI) reagents viz., pyridinium fluorochromate, C5H5NH[CrO3F] (PFC), and quinolinium fluorochromate C9H7NH [CrO3F] (QFC), have been presented. The compounds are capable of acting as both electron-transfer and oxygen-atom-transfer agents. The X-ray analysis of PFC crystals reveals that the compound crystallises in the orthorhombic space group CmcZ1. The structure consists of discrete pyridinium cations and CrO3 F anions with no significant hydrogen bonding. This results in total disorder of the pyridinium cation. The tetrahedral [CrO3 F]− ion lies on a crystallographic mirror plane.

A simple synthesis ofbis(acetylacetonato)dioxouranium(VI) dihydrate, UO2(C5H7O2)2·2H2O

A new and direct route tobis(acetylacetonato)dioxouranium(VI) dihydrate, UO2(C5H7O2)2·2H2O, based upon the reaction of UO3·4H2O with acetylacetone (C5H8O2), is described.

Fluoride assisted stabilization of vanadium(III) and manganese(III) in aqueous medium and efficacy of new fluorochromate(VI) oxidants

Abstract The importance of F − as a stabilizing ligand for V(III) and Mn(III) , both in aqueous solution as well as in solid compounds has been emphasized. A multitude of fluoro and mixed-fluoro complexes have been synthesized from aqueous solution and their structural motif expounded [1]. Routes to VF(C 5 H 7 O 2 ) 2 , Na 3 VF 6 and K 3 VF 6 have been developed based on electron-transfer processes involving vanadium(V) and sacrificial reductants. The coligands for the fluoromanganates(III) have been drawn from SO 4 2− , C 2 O 4 2− , EDTA, HPO 4 2− , glycine, 2,2′-bpy, 1,10-phen, and urea. An internal comparison of the empirical magnetic moments has enabled a magnetostructural correlationship. Pyrolysis of [MnF 3 (urea) 2 ]. 3H 2 O at ca. 500°C affords a potential fluorinating agent, MnF 3 . Efficient and efficacious fluoro-metal oxidants-pyridinium and quinolinium fluorochromates(VI), C 5 H 5 NHCrO 3 F(PFC) [2] and C 9 H 7 NHCrO 3 F(QFC)- have been developed. Typically, PFC in CH 2 Cl 2 oxidizes primary, secondary, and a tricyclic alcohol to the corresponding aldehydes, ketones and a tricyclic enone, benzoin to benzil, and anthracene and phenanthrene to anthraquinone and phenanthrene-9,10-quinone, respectively. Significantly, PFC selectively oxidizes secondary alcohols in the presence of primary ones, participates also in oxygen-transfer reactions (eg. PPh 3 to OPPh 3 ), and qualifies as a valuable new oxidant.