Salt Cluster Attachment to Crown Ether Decorated Phthalocyanines in the Gas Phase

Crown ether decorated phthalocyanines were designed to form rigidly eclipsed aggregates with metal ions being sandwiched between the molecules. We studied tetra-[18]­crown-6 ether functionalized zinc phthalocyanine (ZnPcTetCr) in the presence of excess NaCl by electrospray ionization mass spectrometry. ZnPcTetCr was found to form aggregates in the gas phase to which several neutral NaCl molecules are attached. Collision-induced dissociation experiments revealed that the ions observed in the positive- and negative-ion modes possess remarkably different structures. Their fragmentation behavior indicates that the sodium ions providing the charge of the positively charged aggregates are strongly bound inside the crown ether moieties, while the neutral salt units are less strongly attached. However, in the negatively charged ions, none of the sodium ions is embedded in the crown ether moieties, and the NaCl molecules were found to be attached as one large, weakly bound cluster

Laser Desorption Mass Spectrometry of End Group-Protected Linear Polyynes: Evidence of Laser-Induced Cross-Linking

End group-protected linear polyynes of composition Tr*–(CC)_<i>n</i>–Tr* (with Tr* representing the super trityl group and <i>n</i> = 2, 4, 6, 8, 10) and <i>t</i>Bu–(CC)₆–<i>t</i>Bu (with <i>t</i>Bu being the tertiary butyl group) have been studied by laser desorption ionization (LDI) time-of-flight (ToF) mass spectrometry. <i>t</i>Bu-terminated polyyne molecules show considerably higher stability during laser activation than Tr*-end-capped polyyne molecules. A key feature is the abundant formation of oligomeric species upon laser activation. Tandem mass spectrometry reveals strong bonding within the oligomers which indicates cross-linking of the former polyynes within the oligomers. The process is more abundantly occurring and less energy demanding than the laser-induced coalescence of C₆₀. Cross-linking is more efficient with the smaller end group (<i>t</i>Bu), and larger oligomers are formed when the chain length of the polyyne increases, both a result of enhanced interaction of the triple bonds in neighboring chains. The presence of the matrix molecules in matrix-assisted (MA)­LDI hinders the polyyne interaction, and oligomer formation is markedly reduced

Formation of Singly Bonded Fullerene Dimers in Electrospray Mass Spectrometry

The K⁺ adducts of the crown ether–[60]­fullerene conjugate of the form (12cr4 – H)–C₆₀–H are investigated by electrospray mass spectrometry (ESI-MS), focusing on the dimeric species produced from two different solvent mixtures. A singly bonded fullerene dimer of the type (12cr4 – H)–C₆₀–C₆₀–(12cr4 – H)­K⁺ is generated in aprotic solvents, while in protic solvents, a metal-bridged, noncovalently bound dimer predominates. The dimerization reaction is proposed to occur during the ESI process via the radical intermediate (12cr4 – H)–C₆₀^•. The fragmentation behavior of the different dimers is studied by collision-induced dissociation (CID), showing characteristic product ions for each species

The Influence of Alkali Metal Cation Size on the Formation and Dissociation of Crown Ether Fullerene Dimers in Electrospray Mass Spectrometry

Crown ether fullerenes, C₆₀H­(cr – H), form two different dimers in electrospray ionization mass spectrometry, a noncovalently bound, metal-bridged dimer [C₆₀H­(cr – H)]₂M⁺, and a singly bonded fullerene dimer of the type (cr – H)–C₆₀–C₆₀–(cr – H)­M_<i>n</i>^<i>n</i>+, with <i>n</i> = 1, 2. In this work, the dependence of both the formation and the dissociation of these dimers on the respective sizes of the crown ether moiety (12cr4, 15cr5, 18cr6) and of the alkali metal ion (M⁺ = Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺) is studied. The size ratio of crown ether cavity to metal cation size has a profound influence on the formation of the noncovalent dimers, [C₆₀H­(cr – H)]₂M⁺. These are only formed if the cation is larger than the crown ether cavity. Also, the doubly charged, covalent dimers [C₆₀(cr – H)]₂M₂²⁺ show a dependence on the size ratio. The proposed formation mechanism involves the recombination of two C₆₀(cr – H)­M^•+ radical cations, which can only occur if the repulsion between the two charges is sufficiently reduced by encapsulating the metal cations within the crown ether moiety. Only the formation of the singly charged covalent dimer [C₆₀(cr – H)]₂M⁺ was found to be independent of the size ratio, in line with a radical-based dimerization mechanism. The fragmentation behavior, however, is strongly dependent on the size ratio, revealing the influence of intramolecular crown–metal–crown complexes

Aggregation of a Crown Ether Decorated Zinc–Phthalocyanine by Collision-Induced Desolvation of Electrospray Droplets

The aggregation of phthalocyanines is well-known in solution but has never before been studied in the gas phase. We investigated the tetra-[18]­crown-6 ether functionalized zinc–phthalocyanine (ZnPcTetCr, <b>M</b>) with electrospray ionization mass spectrometry (ESI-MS) in the absence of coordinating metal cations. Apart from the molecular ion <b>M</b>^+•, singly and multiply charged aggregates <b>M</b>_<i>n</i>^{<i>z</i>(+•)} were observed, bound together by electrostatic interactions, without alkali metal cations inside the crown ethers. Collision-induced dissociation (CID) experiments indicate that these clusters consist of stacked neutral <b>M</b> and radical cations <b>M</b>^+•. After the oxidation of individual molecules at the electrospray needle, the aggregation occurs during desolvation of the charged droplets created in the source. Complete evaporation of the solvent and detection of the aggregates was found to require an additional acceleration of the droplets in the transfer region of the instrument, the resulting collisions with neutral gas assisting the desolvation process

Direct Covalent Coupling of Porphyrins to Graphene

Graphene–porphyrin nanohybrid materials with a direct covalent linkage between the graphene carbon network and the functional porphyrin unit have been successfully synthesized via a one-pot reductive diazotation approach. A graphite–potassium intercalation compound (KC₈) was dispersed in THF, and different isolated porphyrin–diazonium salts were added. The direct covalent binding and the detailed characterization of the functional hybrid material were carried out by Raman spectroscopy, TG-MS, UV/vis, and fluorescence spectroscopy. LDI-ToF mass spectrometry was introduced as a new versatile and sensitive tool to investigate covalently functionalized graphene derivatives and to establish the composition of the respective nanohybrid materials

Kinetic Studies of the Reduction of [Co(dmgH)₂(py)(Cl)] Revisited: Mechanisms, Products, and Implications

We report on a mechanistic investigation regarding the reduction of [Co^III(dmgH)₂­(py)­(Cl)] (dmg = dimethylglyoxime) by several complementary techniques. The reduction of [Co^III(dmgH)₂­(py)­(Cl)] was initiated by either electrochemical, photochemical, or pulse radiolytical techniques, and the corresponding products were analyzed by ESI mass spectrometry. In addition, all of the rate constants for each step were determined. We have found solid experimental as well as theoretical evidence for the appearance of a dinuclear complex [Co^IICo^III­(dmgH)₄­(py)₂­(H₂O)₂]⁺ to be the final product of reduction, implying the initially reduced form of [Co^III(dmgH)₂­(py)­(Cl)] undergoes a dimerization with the starting material in solution

Polyoxopalladates Encapsulating 8‑Coordinated Metal Ions, [MO₈Pd^II₁₂L₈]^<i>n</i>− (M = Sc³⁺, Mn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Lu³⁺; L = PhAsO₃^2–, PhPO₃^2–, SeO₃^2–)

A total of 16 discrete polyoxopalladates­(II) [MO₈Pd^II₁₂L₈]^<i>n</i>−, with a metal ion <b>M</b> encapsulated in a cuboid-shaped {Pd₁₂O₈L₈} cage, have been synthesized: the phenylarsonate-capped series (1) <b>L</b> = PhAsO₃^2–, <b>M</b> = Sc³⁺ (<b>ScPhAs</b>), Mn²⁺ (<b>MnPhAs</b>), Fe³⁺ (<b>FePhAs</b>), Co²⁺ (<b>CoPhAs</b>), Ni²⁺ (<b>NiPhAs</b>), Cu²⁺ (<b>CuPhAs</b>), Zn²⁺ (<b>ZnPhAs</b>); the phenylphosphonate-capped series: (2) <b>L</b> = PhPO₃^2–, <b>M</b> = Cu²⁺ (<b>CuPhP</b>), Zn²⁺ (<b>ZnPhP</b>); and the selenite-capped series (3) <b>L</b> = SeO₃^2–, <b>M</b> = Mn²⁺ (<b>MnSe</b>), Fe³⁺ (<b>FeSe</b>), Co²⁺ (<b>CoSe</b>), Ni²⁺ (<b>NiSe</b>), Cu²⁺, (<b>CuSe</b>), Zn²⁺ (<b>ZnSe</b>), Lu³⁺ (<b>LuSe</b>)). The polyanions were prepared in one-pot reactions in aqueous solution of [Pd₃(CH₃COO)₆] with an appropriate salt of the metal ion <b>M</b>, as well as PhAsO₃H₂, PhPO₃H₂, and SeO₂, respectively, and then isolated as hydrated sodium salts Na_<i>n</i>[MO₈Pd^II₁₂L₈]·<i>y</i>H₂O (<i>y</i> = 10–37). The compounds were characterized in the solid state by IR spectroscopy, single-crystal XRD, elemental and thermogravimetric analyses. The solution stability of the diamagnetic polyanions <b>ScPhAs</b>, <b>ZnPhAs</b>, <b>ZnPhP</b>, <b>ZnSe</b>, and <b>LuSe</b> was confirmed by multinuclear (⁷⁷Se, ³¹P, ¹³C, and ¹H) NMR spectroscopy. The polyoxopalladates <b>ScPhAs</b>, <b>MnPhAs</b>, <b>CoPhAs</b>, and <b>CuPhAs</b> were investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS). Electrochemical studies on the manganese- and iron-containing derivatives demonstrated that the redox properties of the Mn²⁺, Fe³⁺, and Pd²⁺ centers in the polyanions are strikingly influenced by the nature of the capping group. These results have subsequently been verified by density functional theory (DFT) calculations. Interestingly, electron paramagnetic resonance (EPR) measurements suggest that the coordination geometry around Mn²⁺ is dynamically distorted on the EPR time scale (∼10^–11 s), whereas it appears as a static ensemble with cubic symmetry on the X-ray diffraction (XRD) time-scale (10^–15 s). The octacoordinated Cu²⁺ cuboid is similarly distorted, in good agreement with DFT calculations. Interestingly, <i>g</i>_∥ is smaller than <i>g</i>_⊥, which is quite unusual, needing further theoretical development