Contribution of thermal energy to initial ion production in matrix-assisted laser desorption/ionization observed with 2,4,6-trihydroxyacetophenone.

RATIONALE: Although several reaction models have been proposed in the literature to explain matrix-assisted laser desorption/ionization (MALDI), further study is still necessary to explore the important ionization pathways that occur under the high-temperature environment of MALDI. 2,4,6-Trihydroxyacetophenone (THAP) is an ideal compound for evaluating the contribution of thermal energy to an initial reaction with minimum side reactions. METHODS: Desorbed neutral THAP and ions were measured using a crossed-molecular beam machine and commercial MALDI-TOF instrument, respectively. A quantitative model incorporating an Arrhenius-type desorption rate derived from transition state theory was proposed. Reaction enthalpy was calculated using GAUSSIAN 03 software with dielectric effect. Additional evidence of thermal-induced proton disproportionation was given by the indirect ionization of THAP embedded in excess fullerene molecules excited by a 450 nm laser. RESULTS: The quantitative model predicted that proton disproportionation of THAP would be achieved by thermal energy converted from a commonly used single UV laser photon. The dielectric effect reduced the reaction Gibbs free energy considerably even when the dielectric constant was reduced under high-temperature MALDI conditions. With minimum fitting parameters, observations of pure THAP and THAP mixed with fullerene both agreed with predictions. CONCLUSIONS: Proton disproportionation of solid THAP was energetically favorable with a single UV laser photon. The quantitative model revealed an important initial ionization pathway induced by the abrupt heating of matrix crystals. In the matrix crystals, the dielectric effect reduced reaction Gibbs free energy under typical MALDI conditions. The result suggested that thermal energy plays an important role in the initial ionization reaction of THAP.

Copper halide-incorporated tellurium-iron carbonyl complexes: transformation, electrochemical properties, and theoretical calculations.

When the tellurium-capped tri-iron carbonyl cluster [Et(4)N](2)[TeFe(3)(CO)(9)] was treated with 1 equiv of CuX in THF at 0 degrees C, CuX-incorporated clusters [Et(4)N](2)[TeFe(3)(CO)(9)CuX] (X = Cl, [Et(4)N](2)[1a]; Br, [Et(4)N](2)[1b]; I, [Et(4)N](2)[1c]) were formed, respectively. X-ray analysis showed that 1a-1c each exhibited a TeFe(3) core with one Fe-Fe bond bridged by one CuX fragment. When the reactions were carried out at a molar ratio of 1:2 (X = Cl, Br) or 1:3 (X = I) in tetrahydrofuran (THF) or MeCN at 0 degrees C, Cu(2)X(2)-incorporated clusters [Et(4)N](2)[TeFe(3)(CO)(9)Cu(2)X(2)] (X = Cl, [Et(4)N](2)[2a]; Br, [Et(4)N](2)[2b]; I, [Et(4)N](2)[2c]) were obtained, respectively. Cluster 2a was structurally characterized by X-ray analysis to display a TeFe(3) core, in which one TeFe(2) plane was asymmetrically bridged and capped by one mu(3)-CuCl and another mu(4)-CuCl with two Cu atoms bonded. Complexes 1a-1c underwent skeleton expansion to form Cu(3)X-incorporated di-TeFe(3) clusters [{TeFe(3)(CO)(9)}(2)Cu(3)X](2-) (X = Cl, 3a; Br, 3b; I, 3c), respectively, upon treatment with 1 equiv of [Cu(MeCN)(4)][BF(4)] at 0 degrees C. X-ray analysis showed that 3b and 3c each consisted of two TeFe(3) clusters that were linked by a Cu(3)X moiety. However, a similar reaction for 1a and 1b with 1 equiv of [Cu(MeCN)(4)][BF(4)] at room temperature produced Cu(4)X(2)-linked di-TeFe(3) clusters [{TeFe(3)(CO)(9)}(2)Cu(4)X(2)](2-) (X = Cl, 4a; Br, 4b). Cluster 4a was shown by X-ray analysis to have two TeFe(3) cores linked by a Cu(4)Cl(2) moiety. Clusters 4a and 4b were also produced directly from the reaction of [Et(4)N](2)[TeFe(3)(CO)(9)] with 4 equiv of CuX (X = Cl, Br) in THF. Furthermore, the nature, the formation, the cluster transformation, and the electrochemistry of the CuX-incorporated mono- or di-TeFe(3) clusters are explained in terms of the effects of tellurium, copper halide, and the size of the metal skeleton, all of which are elucidated by molecular calculations at the B3LYP level of density functional theory.

Semiconducting tellurium-iron-copper carbonyl polymers.

The unprecedented ternary Te-Fe-Cu chain polymers [{Et4N}{TeFe3(CO)9Cu}]infinity and [{TeFe3(CO)9Cu2}(mu-4,4'-dipyridyl)1.5]infinity were prepared from the self-assembly of [Et4N]2[TeFe3(CO)9] with [Cu(MeCN)4][BF4] in THF or in the presence of 4,4'-dipyridyl in THF. These two chain polymers, which can also be constructed from the precursor complex TeFe3(CO)9Cu2(MeCN)2, show semiconducting behaviors with low band gaps of 0.59 and 0.41 eV, respectively. In addition, their conductivity and the effect of the bridging ligand are further elucidated by theoretical calculations.