A Facile Molecular Approach to Amorphous Nickel Pnictides and Their Reconstruction to Crystalline Potassium-Intercalated γ-NiOOHx Enabling High-Performance Electrocatalytic Water Oxidation and Selective Oxidation of 5-Hydroxymethylfurfural.

The low-temperature molecular precursor approach can be beneficial to conventional solid-state methods, which require high temperatures and lead to relatively large crystalline particles. Herein, a novel, single-step, room-temperature preparation of amorphous nickel pnictide (NiE; EP, As) nanomaterials is reported, starting from NaOCE(dioxane)n and NiBr2 (thf)1.5 . During application for the oxygen evolution reaction (OER), the pnictide anions leach, and both materials fully reconstruct into nickel(III/IV) oxide phases (similar to γ-NiOOH) comprising edge-sharing (NiO6 ) layers with intercalated potassium ions and a d-spacing of 7.27 Å. Remarkably, the intercalated γ-NiOOHx phases are nanocrystalline, unlike the amorphous nickel pnictide precatalysts. This unconventional reconstruction is fast and complete, which is ascribed to the amorphous nature of the nanostructured NiE precatalysts. The obtained γ-NiOOHx can effectively catalyse the OER for 100 h at a high current density (400 mA cm-2 ) and achieves outstandingly high current densities (>600 mA cm-2 ) for the selective, value-added oxidation of 5-hydroxymethylfurfural (HMF). The NiP-derived γ-NiOOHx shows a higher activity for both processes due to more available active sites. It is anticipated that the herein developed, effective, room-temperature molecular synthesis of amorphous nickel pnictide nanomaterials can be applied to other functional transition-metal pnictides.

Evolution of Carbonate-Intercalated γ-NiOOH from a Molecularly Derived Nickel Sulfide (Pre)Catalyst for Efficient Water and Selective Organic Oxidation.

The development of a competent (pre)catalyst for the oxygen evolution reaction (OER) to produce green hydrogen is critical for a carbon-neutral economy. In this aspect, the low-temperature, single-source precursor (SSP) method allows the formation of highly efficient OER electrocatalysts, with better control over their structural and electronic properties. Herein, a transition metal (TM) based chalcogenide material, nickel sulfide (NiS), is prepared from a novel molecular complex [NiII (PyHS)4 ][OTf]2 (1) and utilized as a (pre)catalyst for OER. The NiS (pre)catalyst requires an overpotential of only 255 mV to reach the benchmark current density of 10 mA cm-2 and shows 63 h of chronopotentiometry (CP) stability along with over 95% Faradaic efficiency in 1 m KOH. Several ex situ measurements and quasi in situ Raman spectroscopy uncover that NiS irreversibly transformed to a carbonate-intercalated γ-NiOOH phase under the alkaline OER conditions, which serves as the actual active structure for the OER. Additionally, this in situ formed active phase successfully catalyzes the selective oxidation of alcohol, aldehyde, and amine-based organic substrates to value-added chemicals, with high efficiencies.

Spectroscopic Properties of a Biologically Relevant [Fe2 (µ-O)2 ] Diamond Core Motif with a Short Iron-Iron Distance.

Diiron cofactors in enzymes perform diverse challenging transformations. The structures of high valent intermediates (Q in methane monooxygenase and X in ribonucleotide reductase) are debated since Fe-Fe distances of 2.5-3.4 Šwere attributed to "open" or "closed" cores with bridging or terminal oxido groups. We report the crystallographic and spectroscopic characterization of a FeIII 2 (µ-O)2 complex (2) with tetrahedral (4C) centres and short Fe-Fe distance (2.52 Å), persisting in organic solutions. 2 shows a large Fe K-pre-edge intensity, which is caused by the pronounced asymmetry at the TD FeIII centres due to the short Fe-µ-O bonds. A ≈2.5 ŠFe-Fe distance is unlikely for six-coordinate sites in Q or X, but for a Fe2 (µ-O)2 core containing four-coordinate (or by possible extension five-coordinate) iron centres there may be enough flexibility to accommodate a particularly short Fe-Fe separation with intense pre-edge transition. This finding may broaden the scope of models considered for the structure of high-valent diiron intermediates formed upon O2 activation in biology.

Deoxygenation of Nitrous Oxide and Nitro Compounds Using Bis(N-Heterocyclic Silylene)Amido Iron Complexes as Catalysts.

Herein, we report the efficient degradation of N2 O with a well-defined bis(silylene)amido iron complex as catalyst. The deoxygenation of N2 O using the iron silanone complex 4 as a catalyst and pinacolborane (HBpin) as a sacrificial reagent proceeds smoothly at 50 °C to form N2 , H2 , and (pinB)2 O. Mechanistic studies suggest that the iron-silicon cooperativity is the key to this catalytic transformation, which involves N2 O activation, H atom transfer, H2 release and oxygenation of the boron sites. This approach has been further developed to enable catalytic reductions of nitro compounds, producing amino-boranes with good functional-group tolerance and excellent chemoselectivity.

Boosting homogeneous chemoselective hydrogenation of olefins mediated by a bis(silylenyl)terphenyl-nickel(0) pre-catalyst.

The isolable chelating bis(N-heterocyclic silylenyl)-substituted terphenyl ligand [SiII(Terp)SiII] as well as its bis(phosphine) analogue [PIII(Terp)PIII] have been synthesised and fully characterised. Their reaction with Ni(cod)2 (cod = cycloocta-1,5-diene) affords the corresponding 16 VE nickel(0) complexes with an intramolecular η 2-arene coordination of Ni, [E(Terp)E]Ni(η 2-arene) (E = PIII, SiII; arene = phenylene spacer). Due to a strong cooperativity of the Si and Ni sites in H2 activation and H atom transfer, [SiII(Terp)SiII]Ni(η 2-arene) mediates very effectively and chemoselectively the homogeneously catalysed hydrogenation of olefins bearing functional groups at 1 bar H2 pressure and room temperature; in contrast, the bis(phosphine) analogous complex shows only poor activity. Catalytic and stoichiometric experiments revealed the important role of the η2-coordination of the Ni(0) site by the intramolecular phenylene with respect to the hydrogenation activity of [SiII(Terp)SiII]Ni(η 2-arene). The mechanism has been established by kinetic measurements, including kinetic isotope effect (KIE) and Hammet-plot correlation. With this system, the currently highest performance of a homogeneous nickel-based hydrogenation catalyst of olefins (TON = 9800, TOF = 6800 h-1) could be realised.

Evolving Highly Active Oxidic Iron(III) Phase from Corrosion of Intermetallic Iron Silicide to Master Efficient Electrocatalytic Water Oxidation and Selective Oxygenation of 5-Hydroxymethylfurfural.

In a green energy economy, electrocatalysis is essential for chemical energy conversion and to produce value added chemicals from regenerative resources. To be widely applicable, an electrocatalyst should comprise the Earth's crust's most abundant elements. The most abundant 3d metal, iron, with its multiple accessible redox states has been manifold applied in chemocatalytic processes. However, due to the low conductivity of FeIII Ox Hy phases, its applicability for targeted electrocatalytic oxidation reactions such as water oxidation is still limited. Herein, it is shown that iron incorporated in conductive intermetallic iron silicide (FeSi) can be employed to meet this challenge. In contrast to silicon-poor iron-silicon alloys, intermetallic FeSi possesses an ordered structure with a peculiar bonding situation including covalent and ionic contributions together with conducting electrons. Using in situ X-ray absorption and Raman spectroscopy, it could be demonstrated that, under the applied corrosive alkaline conditions, the FeSi partly forms a unique, oxidic iron(III) phase consisting of edge and corner sharing [FeO6 ] octahedra together with oxidized silicon species. This phase is capable of driving the oxyge evolution reaction (OER) at high efficiency under ambient and industrially relevant conditions (500 mA cm-2 at 1.50 ± 0.025 VRHE and 65 °C) and to selectively oxygenate 5-hydroxymethylfurfural (HMF).

Well-Defined, Silica-Supported Homobimetallic Nickel Hydride Hydrogenation Catalyst.

There is an increasing interest to replace precious metal-based catalysts by earth-abundant nonprecious metals due to higher costs, toxicity, and declining availability of the former. Here, the synthesis of a well-defined supported nickel hydrogenation catalyst prepared by surface organometallic chemistry is reported. For this purpose, [LNi(µ-H)]2 (L = HC(CMeNC6H3(iPr)2)2) was grafted on partially dehydroxylated silica to give a homobimetallic H- and O(silica)-bridged Ni2 complex. The structure of the latter was confirmed by infrared spectroscopy, X-ray absorption near-edge structure, and extended X-ray absorption fine structure analyses as well as hydride titration studies. The immobilized catalyst was capable of hydrogenating alkenes and alkynes at low temperatures without prior activation. As an example, ethene can be hydrogenated with an initial turnover frequency of 25.5 min-1 at room temperature.

Facile Access to an Active γ-NiOOH Electrocatalyst for Durable Water Oxidation Derived From an Intermetallic Nickel Germanide Precursor.

Identifying novel classes of precatalysts for the oxygen evolution reaction (OER by water oxidation) with enhanced catalytic activity and stability is a key strategy to enable chemical energy conversion. The vast chemical space of intermetallic phases offers plenty of opportunities to discover OER electrocatalysts with improved performance. Herein we report intermetallic nickel germanide (NiGe) acting as a superior activity and durable Ni-based electro(pre)catalyst for OER. It is produced from a molecular bis(germylene)-Ni precursor. The ultra-small NiGe nanocrystals deposited on both nickel foam and fluorinated tin oxide (FTO) electrodes showed lower overpotentials and a durability of over three weeks (505 h) in comparison to the state-of-the-art Ni-, Co-, Fe-, and benchmark NiFe-based electrocatalysts under identical alkaline OER conditions. In contrast to other Ni-based intermetallic precatalysts under alkaline OER conditions, an unexpected electroconversion of NiGe into γ-NiIII OOH with intercalated OH- /CO3 2- transpired that served as a highly active structure as shown by various ex situ methods and quasi in situ Raman spectroscopy.

Immobilization of an Iridium Pincer Complex in a Microporous Polymer for Application in Room-Temperature Gas Phase Catalysis.

An iridium dihydride pincer complex [IrH2 (POCOP)] is immobilized in a hydroxy-functionalized microporous polymer network using the concepts of surface organometallic chemistry. The introduction of this novel, truly innocent support with remote OH-groups enables the formation of isolated active metal sites embedded in a chemically robust and highly inert environment. The catalyst maintained high porosity and without prior activation exhibited efficacy in the gas phase hydrogenation of ethene and propene at room temperature and low pressure. The catalyst can be recycled for at least four times.

Cycloaddition Chemistry of a Silylene-Nickel Complex toward Organic π-Systems: From Reversibility to C-H Activation.

The versatile cycloaddition chemistry of the Si-Ni multiple bond in the acyclic (amido)(chloro)silylene→Ni0 complex 1, [(TMS L)ClSi→Ni(NHC)2 ] (TMS L=N(SiMe3 )Dipp; Dipp=2,6-iPr2 C6 H4 ; NHC=C[(iPr)NC(Me)]2 ), toward unsaturated organic substrates is reported, which is both reminiscent of and expanding on the reactivity patterns of classical Fischer and Schrock carbene-metal complexes. Thus, 1:1 reaction of 1 with aldehydes, imines, alkynes, and even alkenes proceed to yield [2+2] cycloaddition products, leading to a range of four-membered metallasilacycles. This cycloaddition is in fact reversible for ethylene, whereas addition of an excess of this olefin leads to quantitative sp2 -CH bond activation, via a 1-nickela-4-silacyclohexane intermediate. These results have been supported by DFT calculations giving insights into key mechanistic aspects.

A soft molecular 2Fe-2As precursor approach to the synthesis of nanostructured FeAs for efficient electrocatalytic water oxidation.

An unprecedented molecular 2Fe-2As precursor complex was synthesized and transformed under soft reaction conditions to produce an active and long-term stable nanocrystalline FeAs material for electrocatalytic water oxidation in alkaline media. The 2Fe2As-centred ß-diketiminato complex, having an unusual planar Fe2As2 core structure, results from the salt-metathesis reaction of the corresponding ß-diketiminato FeIICl complex and the AsCO- (arsaethynolate) anion as the monoanionic As- source. The as-prepared FeAs phase produced from the precursor has been electrophoretically deposited on conductive electrode substrates and shown to act as a electro(pre)catalyst for the oxygen evolution reaction (OER). The deposited FeAs undergoes corrosion under the severe anodic alkaline conditions which causes extensive dissolution of As into the electrolyte forming finally an active two-line ferrihydrite phase (Fe2O3(H2O) x ). Importantly, the dissolved As in the electrolyte can be fully recaptured (electro-deposited) at the counter electrode making the complete process eco-conscious. The results represent a new and facile entry to unexplored nanostructured transition-metal arsenides and their utilization for high-performance OER electrocatalysis, which are also known to be magnificent high-temperature superconductors.

Boosting Electrocatalytic Hydrogen Evolution Activity with a NiPt3@NiS Heteronanostructure Evolved from a Molecular Nickel-Platinum Precursor.

A facile synthetic route to NiPt3@NiS heteronanostructures is reported, starting from a subsulfido bridged heterobimetallic nickel-platinum molecular precursor. Notably, the NiPt3@NiS on nickel foam displayed merely an overpotential of 12 mV at -10 mA cm-2, which is substantially lower than that of Pt or NiS, synthesized through a similar approach and represents the most active hydrogen evolution reaction (HER) electrocatalysts yet reported in alkaline solutions. NiPt3@NiS electrodes demonstrated an unceasing HER stability over 8 days, which is well over those reported for Pt-based catalysts signifying a capability of scaled hydrogen production.

Versatile Tautomerization of EH2-Substituted Silylenes (E = N, P, As) in the Coordination Sphere of Nickel.

The synthesis and tautomerization of a "half-parent" aminosilylene and its heavy P- and As-analogues (TMSLSi-EH2; E = N, P, As; TMSL = N(SiMe3)(2,6- iPr2C6H3)) in the coordination sphere of nickel(0) to give the corresponding side-on η2-RSi(H)═EH and RH2Si-E ("silylpnictinidene") nickel complexes are reported. These complexes can be accessed through salt metathesis reactions of the lithium dihydropnictides LiEH2 with the acyclic chlorosilylene nickel(0) complex 1, [TMSL(Cl)Si → Ni(NHC)2; NHC = :C[( iPr)NC(Me)]2). In addition, we report the facile E-H bond activation reactions of EH3 with 1, which furnished a silyl nickel(II) complex through NH3 activation, but phosphido and arsenido complexes in the activation of PH3 and AsH3, respectively. Notably, reaction of 1 with LiNH2 leads to the acyclic bis(amido)silylene complex [TMSL(H2N)Si → Ni(NHC)2] 5, which does not undergo N-H proton migration to silicon(II) under ambient conditions. The transformation of the P- and As-analogues of 1 furnishes directly the respective side-on Si═E Ni complexes (nickelacycles), [η2-{TMSL(H)Si═E(H)}Ni(NHC)2] (E = P, 6; E = As, 9). These nickelacycles show a vastly different stability in solutions. While 6 is stable for several days at ambient temperature, 9 undergoes further rearrangement processes within minutes of its formation. Given the high acidity of the As-H proton in 9, however, this moiety can be trapped as a highly charge separated metalated-η2-silaarsene nickel complex 12 that is best described as an [AsSiNi] nickelacycle with Si-As multiple bond character. Taken as a whole, these results give, for the first time, insights into the relative stability of the tautomeric forms of side-on silaldimine transition metal complexes. The electronic nature and the rearrangement processes of these compounds were also investigated by quantum chemical calculations.

From As-Zincoarsasilene (LZn-As=SiL') to Arsaethynolato (As≡C-O) and Arsaketenylido (O=C=As) Zinc Complexes.

The reactivity of the As-zincosilaarsene LZn-As=SiL' A (L=[CH(CMeNDipp)2 ]- , Dipp=2,6-i Pr2 C6 H3 , L'=[{C(H)N(2,6-i Pr2 -C6 H3 )}2 ]2- ) towards small molecules was investigated. Due to the pronounced zwitterionic character of the Si=As bond of A, it undergoes addition reactions with H2 O and NH3 , forming LZnAs(H)SiOH(L') 1 and LZnAs(H)SiNH2 (L') 2. Oxygenation of A with N2 O at -60 °C furnishes the deep blue 1,2-disiloxydiarsene, [LZnOSi(L')As]2 4, presumably via dimerization of the arsinidene intermediate LZnOSi(L')As 3. Oxygenation of A with CO2 leads to the monomeric arsaethynolato siloxido zinc complex LZnOSi(L')(OC≡As) 5, essentially trapping the intermediary arsinidene 3 with liberated CO following initial oxidation of the Si=As bond. DFT calculations confirm the ambident coordination mode of the anionic [AsCO] ligand in solution, with the O-arsaethynolato [As≡C-O].- in 5, and the As-arsaketenylido ligand mode [O=C=As]- present in LZnO-Si(L')(-As=C=O) 5' akin to the analogous phosphorus system, [PCO]- .

Nucleophilic versus Electrophilic Reactivity of Bioinspired Superoxido Nickel(II) Complexes.

The formation and detailed spectroscopic characterization of the first biuret-containing monoanionic superoxido-NiII intermediate [LNiO2 ]- as the Li salt [2; L=MeN[C(=O)NAr)2 ; Ar=2,6-iPr2 C6 H3 )] is reported. It results from oxidation of the corresponding [Li(thf)3 ]2 [LNiII Br2 ] complex M with excess H2 O2 in the presence of Et3 N. The [LNiO2 ]- core of 2 shows an unprecedented nucleophilic reactivity in the oxidative deformylation of aldehydes, in stark contrast to the electrophilic character of the previously reported neutral Nacnac-containing superoxido-NiII complex 1, [L'NiO2 ] (L'=CH(CMeNAr)2 ). According to density-functional theory (DFT) calculations, the remarkably different behaviour of 1 versus 2 can be attributed to their different charges and a two-state reactivity, in which a doublet ground state and a nearby spin-polarized doublet excited-state both contribute in 1 but not in 2. The unexpected nucleophilicity of the superoxido-NiII core of 2 suggests that such a reactivity may also play a role in catalytic cycles of Ni-containing oxygenases and oxidases.

From zinco(ii) arsaketenes to silylene-stabilised zinco arsinidene complexes.

The decarbonylation of the first zinco(ii) arsaketene complexes LZnAsCO (2) and LZn(AsCO)(NHC) (4) (L = {CH(CMeNDipp)2}-, Dipp = 2,6-iPr2C6H3; NHC = [C(Me)N(iPr)]2C:) has been investigated in the presence of the N-heterocyclic silylenes, tBuNHSi (tBuNHSi = [C(H)N(tBu)]2Si:) and DippNHSi (DippNHSi = [C(H)N(2,6-iPr2-C6H3)]2Si:). Depending on the steric demand of the NHSi donor, dimers or monomers of silylene-stabilised arsinidenes are isolated. The bonding situations in all of the novel arsinidene complexes have been elucidated through X-ray diffraction analyses and theoretical calculations.

Bis(silylenyl)-substituted ferrocene-stabilized η6-arene iron(0) complexes: synthesis, structure and catalytic application.

Reaction of FeX2(thf)n (X = Cl n = 1.5, Br n = 2) with the chelating 1,1'-bis(silylenyl)-substituted ferrocene ligand SiFcSiA (Fc = ferrocendiyl, Si = PhC(NtBu)2Si:) furnishes the corresponding dihalido Fe(ii) complexes [(SiFcSi)FeX2] (X = Cl, 1 and X = Br, 2) in high yields. Reduction of the latter with an excess of KC8 in the presence of benzene and toluene leads to the unprecedented bis(silylene) stabilized Fe0 complexes [(SiFcSi)Fe-η6(C6H6)] 3 and [(SiFcSi)Fe-η6(C7H8)] 4, respectively. The 57Fe Mössbauer spectrum of 3 at 13 K exhibits parameters (σ = 0.3676 mm s-1; ΔEQ = 1.334 mm s-1) which are consistent with the presence of a pentacoordinated Fe0 atom in a pseudo trigonal-bipyramidal coordination environment, with two dative Si→Fe bonds and three coordination sites occupied by the η6-coordinated arene ligand. Results from DFT calculations, 57Fe Mössbauer parameters and the diamagnetic NMR spectra confirm the redox-innocent nature of these ligands and the zero oxidation state of the iron center. The catalytic ability of 3 was investigated with respect to ketone hydrogenation. In all cases, good to excellent yields to the corresponding alcohols were obtained at 50 °C and 50 bar H2 pressure. Electron-donating as well as -withdrawing substituents were tolerated with excellent to good yields. Conversions of bulkier ketones and unactivated aliphatic ketones lead merely to moderate yields. This represents the first example of a silylene-iron metal complex which has been utilized as a highly active precatalyst in the hydrogenation of ketones. The results underline the powerful ability of chelating bis(N-heterocyclic silylene) ligands acting as strong σ-donor ligands in stabilizing a new generation of low-valent, electron-rich transition metal complexes for catalytic transformations.

Divalent Silicon-Assisted Activation of Dihydrogen in a Bis(N-heterocyclic silylene)xanthene Nickel(0) Complex for Efficient Catalytic Hydrogenation of Olefins.

The first chelating bis(N-heterocyclic silylene)xanthene ligand [SiII(Xant)SiII] as well as its Ni complexes [SiII(Xant)SiII]Ni(η2-1,3-cod) and [SiII(Xant)SiII]Ni(PMe3)2 were synthesized and fully characterized. Exposing [SiII(Xant)SiII]Ni(η2-1,3-cod) to 1 bar H2 at room temperature quantitatively generated an unexpected dinuclear hydrido Ni complex with a four-membered planar Ni2Si2 core. Exchange of the 1,3-COD ligand by PMe3 led to [SiII(Xant)SiII]Ni(PMe3)2, which could activate H2 reversibly to afford the first SiII-stabilized mononuclear dihydrido Ni complex characterized by multinuclear NMR and single-crystal X-ray diffraction analysis. [SiII(Xant)SiII]Ni(η2-1,3-cod) is a strikingly efficient precatalyst for homogeneous hydrogenation of olefins with a wide substrate scope under 1 bar H2 pressure at room temperature. DFT calculations reveal a novel mode of H2 activation, in which the SiII atoms of the [SiII(Xant)SiII] ligand are involved in the key step of H2 cleavage and hydrogen transfer to the olefin.

From a Molecular 2Fe-2Se Precursor to a Highly Efficient Iron Diselenide Electrocatalyst for Overall Water Splitting.

A highly active FeSe2 electrocatalyst for durable overall water splitting was prepared from a molecular 2Fe-2Se precursor. The as-synthesized FeSe2 was electrophoretically deposited on nickel foam and applied to the oxygen and hydrogen evolution reactions (OER and HER, respectively) in alkaline media. When used as an oxygen-evolution electrode, a low 245 mV overpotential was achieved at a current density of 10 mA cm-2 , representing outstanding catalytic activity and stability because of Fe(OH)2 /FeOOH active sites formed at the surface of FeSe2 . Remarkably, the system is also favorable for the HER. Moreover, an overall water-splitting setup was fabricated using a two-electrode cell, which displayed a low cell voltage and high stability. In summary, the first iron selenide material is reported that can be used as a bifunctional electrocatalyst for the OER and HER, as well as overall water splitting.

Spectroscopic Characterization, Computational Investigation, and Comparisons of ECX- (E = As, P, and N; X = S and O) Anions.

Three newly synthesized [Na+(221-Kryptofix)] salts containing AsCO-, PCO-, and PCS- anions were successfully electrosprayed into a vacuum, and these three ECX- anions were investigated by negative ion photoelectron spectroscopy (NIPES) along with high-resolution photoelectron imaging spectroscopy. For each ECX- anion, a well-resolved NIPE spectrum was obtained, in which every major peak is split into a doublet. The splittings are attributed to spin-orbit coupling (SOC) in the ECX• radicals. Vibrational progressions in the NIPE spectra of ECX- were assigned to the symmetric and the antisymmetric stretching modes in ECX• radicals. The electron affinities (EAs) and SO splittings of ECX• are determined from the NIPE spectra to be AsCO•: EA = 2.414 ± 0.002 eV, SO splitting = 988 cm-1; PCO•: EA = 2.670 ± 0.005 eV, SO splitting = 175 cm-1; PCS•: EA = 2.850 ± 0.005 eV, SO splitting = 300 cm-1. Calculations using the B3LYP, CASPT2, and CCSD(T) methods all predict linear geometries for both the anions and the neutral radicals. The calculated EAs and SO splittings for ECX• are in excellent agreement with the experimentally measured values. The simulated NIPE spectra, which are based on the calculated Franck-Condon factors, and the SO splittings nicely reproduce all of the observed spectral peaks, thus allowing unambiguous spectral assignments. The finding that PCS• has the greatest EA of the three triatomic molecules considered here is counterintuitive based upon simple electronegativity considerations, but this finding is understandable in terms of the movement of electron density from phosphorus in the HOMO of PCO- to sulfur in the HOMO of PCS-. Comparisons of the EAs of PCO• and PCS• with the previously measured EA values for NCO• and NCS• are made and discussed.