Speciation of Main-Group Metal Ions by Electrospray Mass Spectrometry. 1. Investigation of Aqueous Polyselenide Species and Effects of Cations and pH

Abstract

Polyselenide anion speciation in aqueous solution has been investigated by electrospray mass spectrometry (ESMS). Two methods of control over this speciation are reported: countercation substitutions and pH adjustments. The countercation has been found to affect the degree of disproportionation or comproportionation. Solutions of sodium tetraselenide displayed numerous Se n 2and HSe n -species in neutral and basic soluions. In potassium solutions, the dominant species was Se 4 2-‚H 2 O. Solutions of cesium pentaselenide also showed preference for higher-order polyselenides. The pH dependence has been analyzed in terms of the percent Se n (n ) 2-5) present. Di-, tri-, tetra-, and pentaselenide species were present over the entire pH range investigated, and trends in selenide species versus pH were developed. For example, at pH > 9, tetraselenide species were dominant.

Organic Cation and Complex Cation‐Stabilized (Poly‐)Selenides, [Cation]x(Sey)z: Diversity in Structures and Properties

“…The existence of a (Se 5 ) 2– species in solution was determined by electrospray ionization mass spectroscopy (ESI‐MS) and further studies on pH dependencies and the impact of different counterions were elucidated by Dorhout and co‐workers 74. However, further mass spectrometric data have not been reported to date.…”

Hexacaesium nonaselenidotetraantimonate(III) hemihydrate

“…We now report the preparation and structure of Cs 6 Sb 4 Se 9 Á0.5H 2 O, which contains the novel discrete [Sb 4 Se 9 ] 6À chain anion ( Fig. 1) not found by Raymond et al (1997) for the K + /Sb/Se system. Three caesium selenidoantimonates, CsSbSe 2 (Kanishcheva et al, 1980), CsSb 2 Se 4 (Sheldrick & Kaub, 1986) and Cs 3 Sb 5 Se 9 (Sheldrick & Hä usler, 1988) had been structurally characterized prior to this study.…”

“…Although electrospray mass spectrometric measurements on the K + /Sb/Se system in dimethylformamide (DMF) have confirmed the presence of the corner-bridged oligomeric anions [Sb 2 Se 5 ] 4À (Raymond et al, 1997) 6À , only the first of these selenidoantimonate(III) anions has been characterized in the solid state. Both [Fe(en) 3 ] 2 Sb 2 Se 5 (en = ethylenediamine) (Chen et al, 2000) and [Mn(en) 3 ] 2 Sb 2 Se 5 (Nä ther et al, 2003) contain discrete [Sb 2 Se 5 ] 4À anions comprising two corner-bridged SbSe 3 pyramids.…”

Specific Induced Circular Dichroism and Enhanced B to Z Transitions of Duplexes Stabilized by Chromophore‐Linked Alkynylnucleoside Residues

“…On dissolving selenium to saturation under anoxic conditions, the major aqueous species are the HSe – anion at 5 < pH < 8 and Se 4 2– at 9 < pH < 13 in the presence of Na + ions 44. Electrospray MS studies45 have indicated that Se 5 2– anions may also be present at low concentrations in saturated aqueous polyselenide solutions above pH 9 and have confirmed Se 4 2– as the dominant species, regardless of the nature of the alkali metal cation (A = Na + , K + , Cs + ). Individual selenium atoms of an Se n 2– anion can be readily probed by 77 Se NMR, as their chemical shifts increase with distance from the chain end and lie within the wide δ range of 192–860 relative to δ(Me 2 Se) = 0 46.…”