A series of molecular gallium compounds were analyzed using X-ray photoelectron spectroscopy (XPS). Specifically, the Ga 2p3/2 and Ga 3d5/2 photoelectron binding energies and the Ga L3M45M45 Auger electron kinetic energies of compounds with gallium in a range of assigned oxidation numbers and with different stabilizing ligands were measured. Auger parameters were calculated and used to generate multiple chemical speciation (or Wagner) plots that were subsequently used to characterize the novel gallium-cryptand[2.2.2] complexes that possess ambiguous oxidation numbers for gallium. The results presented demonstrate the ability of widely accessible XPS instruments to experimentally determine the chemical state of gallium centers and, as a consequence, provide deeper insights into reactivity compared to assigned oxidation and valence numbers.
Ultrawideline 35Cl solid-state
nuclear magnetic resonance
(SSNMR) spectra of a series of 12 tin chlorides were recorded. The
magnitude of the 35Cl quadrupolar coupling constant (C
Q) was shown to consistently indicate the chemical
state (oxidation number) of the bound Sn center. The chemical state
of the Sn center was independently verified by tin Mössbauer
spectroscopy. C
Q(35Cl) values
of >30 MHz correspond to Sn(IV), while C
Q(35Cl) readings of <30 MHz indicate that Sn(II) is
present. Tin-119 SSNMR experiments would seem to be the most direct
and effective route to interrogating tin in these systems, yet we
show that ambiguous results can emerge from this method, which may
lead to an incorrect interpretation of the Sn oxidation number. The
accumulated 35Cl NMR data are used as a guide to assign
the Sn oxidation number in the mixed-valent metal complex Ph3PPdImSnCl2. The synthesis and crystal structure
of the related Ph3PPtImSnCl2 are
reported, and 195Pt and 35Cl SSNMR experiments
were also used to investigate its Pt–Sn bonding. Plane-wave
DFT calculations of 35Cl, 119Sn, and 195Pt NMR parameters are used to model and interpret experimental data,
supported by computed 119Sn and 195Pt chemical
shift tensor orientations. Given the ubiquity of directly bound Cl
centers in organometallic and inorganic systems, there is tremendous
potential for widespread usage of 35Cl SSNMR parameters
to provide a reliable indication of the chemical state in metal chlorides.
The NH activation of ammonia by tetramesityldisilene takes place in three steps: formation of the anti-ammonia-disilene adduct, inversion at the β-silicon, and intramolecular syn-transfer of the proton to give the syn-product.
The synthesis and characterization of two bimetallic, cationic low-valent gallium-cryptand[2.2.2] complexes is reported. The reaction of cryptand[2.2.2] with Ga2Cl4 gave two different cations, [Ga3Cl4 (crypt-222)](+) (1) or [Ga2Cl2 (crypt-222)](2+) (2), depending on whether or not trimethylsilyl triflate (Me3SiOTf) was added as a co-reagent. Complexes 1 and 2 are the first examples of bimetallic cryptand[2.2.2] complexes, as well as the first low-valent gallium-cryptand[2.2.2] complexes. Computational methods were used to evaluate the bonding in the gallium cores.
The
synthesis and reactivity of a gallium(I) cationic complex using
[12]crown-4 as a stabilizing ligand were explored. The synthesis of
[Ga([12]crown-4)][GaCl4] was achieved in one
step from commercially available starting materials. Anion exchange
was utilized to replace the reactive tetrachlorogallate anion for
the perfluorophenylborate anion. [Ga([12]crown-4)][B(C6F5)4] was analyzed using XPS, which
allowed for the classification of the gallium(I)-crown ether complex
as electron-deficient. Reactions of the gallium(I)-crown ether complex
with Cp*K and cryptand[2.2.2] demonstrated the facile synthesis of
a known gallium(I) compound as well as the generation of new gallium(I)
complexes, highlighting the use of the gallium(I)-crown ether complex
as an effective starting material for new gallium(I) complexes.
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