Electrospray ionization mass spectrometry of the cerium(III)-phosphomolybdate complex (NH 4 ) 11 Ce(PMo 11 O 39 ) 2
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Electrospray ionization mass spectrometry of the cerium(III)-phosphomolybdate complex (NH4)11Ce(PMo11O39)2 Travis H. Bray, Roy Copping, David K. Shuh, and John K. Gibson Chemical Sciences Division, The Glenn T. Seaborg Center, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., MS 70A-1150, Berkeley, California, 94720 USA ABSTRACT Electrospray ionization quadrupole ion trap mass spectrometry of the ammonium lanthanide(III) phosphomolybdate complex (NH4)11Ce(III)(PMo11O39)2 has been conducted revealing the Ce-POM complexes H2Ce(III)P2Mo22O753- and Ce(III)PMollO382- as the primary Ce species in 10 mM solutions. From the complex isotopic fingerprints produced through the assembly of multiple molybdenum atoms, a transition metal with seven naturally occurring isotopes, the identities of larger ions were confirmed via successive collision induced dissociation (CID) studies of the gas phase ions. The result of these CID studies was the production of smaller ions with reduced molybdenum content, allowing for comparison between calculated and experimental isotopic distributions. CID studies also provided insights into favored fragmentation pathways. These studies provide a basis to explore speciation and ESI behavior of actinide cluster complexes. INTRODUCTION The photophysical, catalytic, and magnetic properties of lanthanide polyoxometalate (LnPOM) complexes have been extensively studied, yielding potential applications in many fields, including medicine, materials science, imaging and sensing, and industrial processes [1]. The potential presence of Keggin-based phosphomolybdate anions in nuclear waste spurred systematic solution and solid state investigations into their complexation of trivalent lanthanides [2, 3]. The structure of the dumbbell-shaped bis-complex (NH4)11Ce(PMo11O39)2 has been identified as a Ce(III) metal ion residing in the vacancies of two lacunary phophomolybdates (Fig. 1). A comparison of solution and solid-state IR and 31P NMR spectra show good correlation between both P-O band splitting and chemical shift, respectively. These results provide evidence that this complex is stable in solution, as well as the solid-state. While effort has been devoted to studying trivalent Ln-POMs, as well as the complexation of the tetravalent metals Ce, Th, Zr, and Hf, in the condensed phase [4, 5], little has been reported with regard to the gas-phase chemistry of POM-coordinated f–block metal complexes. However, electrospray ionization mass spectrometry (ESI/MS) analyses of related complexes have been reported
Fig. 1. Polyhedral representation of the 2:1 Ce-phosphomolybdate complex [Ce(PMo11O39)2]11-.
outlining the complex behavior of iso- and heteropolyoxometalates during transference from solution to gas [6 - 15]. The recent seminal work of Ma, et al. established a systematic approach to studying the collision induced dissociation (CID) gas fragmentation of lacunary and plenary Keggin phosphotungstates, as well as the mixed metal Keggin derivatives Co(II)PW11O382- and Fe(III)PW11O392-, the Daw
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