Unusual products observed in gas-phase WxOy−+H2O and D2O reactions

Abstract

Addition of H(2)O and D(2)O to small tungsten suboxide cluster anions W(x)O(y)(-) (x = 1-4; y < or = 3x) was studied using mass spectrometric measurements from a high-pressure fast flow reactor. Within the WO(y)(-) mass manifold, which also includes WO(4)H(-), product masses correspond to the addition of one to three H(2)O or D(2)O molecules. Within the W(2)O(y)(-) cluster series, product distributions suggest that sequential oxidation W(2)O(y)(-) + H(2)O/D(2)O --> W(2)O(y+1)(-) + H(2)/D(2) occurs for y < 5, while for W(2)O(5)(-), W(2)O(6)H(2)(-)/W(2)O(6)D(2)(-) is primarily produced. W(2)O(6)(-) does not appear reactive. For the W(3)O(y)(-) cluster series, sequential oxidation with H(2) and D(2) production occurs for y < 6, while W(3)O(6)(-) and W(3)O(7)(-) produce W(3)O(7)H(2)(-)/W(3)O(7)D(2)(-) and W(3)O(8)H(2)(-)/W(3)O(8)D(2)(-), respectively. Lower mass resolution in the W(4)O(y)(-) mass range prevents definitive product assignments, but intensity patterns suggest that sequential oxidation with H(2)/D(2) evolution occurs for y < 6, while W(4)O(y+1)H(2)(-)/W(4)O(y+1)D(2)(-) products result from addition to W(4)O(6)(-) and W(4)O(7)(-). Based on bond energy arguments, the H(2)/D(2) loss reaction is energetically favored if the new O-W(x)O(y)(-) bond energy is greater than 5.1 eV. The relative magnitude of the rate constants for sequential oxidation and H(2)O/D(2)O addition for the x = 2 series was determined. There are no discernable differences in rate constants for reactions with H(2)O or D(2)O, suggesting that the H(2) and D(2) loss from the lower-oxide/hydroxide intermediates is very fast relative to the addition of H(2)O or D(2)O.

Closed-Cage Tungsten Oxide Clusters in the Gas Phase

“…Our optimized geometrical parameters compare well with crystal structure suggesting that the tungsten cluster optimization is fairly accurate to derive the structural and thermodynamic parameters. The infrared spectrum of W 6 O 19 2-is shown in Figure 11 2-is shown in Figure 12a. The density plot clearly reveals the delocalization of the anionic electron density over three inequivalent subunits of W-O cluster moieties of the W 6 O 19 2-system.…”

“…16 Various kinds of metal-carbon cage clusters were explored in great detail by Guo et al 17 Molecular level details of small WO clusters on oxidative catalysis have been reported by Johnson et al 18 recently. Rothgeb et al 19 reported the unusual reactivity of small anionic WO clusters with H 2 O and D 2 O.…”

RH and H2 Production in Reactions between ROH and Small Molybdenum Oxide Cluster Anions

“…Additionally, in Figure 4b, a low-intensity product peak with mass corresponding to Mo 4 36,37 To compare those rate constants to the rates of Mo x O y − + ROH reactions, the same analysis will be applied here. Individual oxide peaks in the x = 2 and 3 manifolds of Mo x O y − vary as a function of alcohol (ROH) number density present in the reactor.…”

“…The HO−H bond dissociation energy is 1.17 eV higher than the CH 3 −OH bond dissociation energy, which may explain why abstraction products were not observed in the cluster−water reactivity studies. 36,37 The most predominant product peak, …”

CexOy– (x = 2–3) + D2O Reactions: Stoichiometric Cluster Formation from Deuteroxide Decomposition and Anti-Arrhenius Behavior

“…11,30,31 Cluster anions were generated in an ablation source using the second harmonic output of a Nd:YAG laser (5 mJ/pulse) focused onto a target prepared from pressed cerium powder (Sigma-Aldrich Co., St. Louis, MO). The resulting plasma coalesced and cooled and was swept through the 2.5 cm long, 0.3 cm diameter reaction channel in a pulse of ultra-highpurity helium issued from a solenoid-type molecular beam valve (BV1), synchronized with the laser.…”