Electrochemical and Theoretical Investigations of the Role of the Appended Base on the Reduction of Protons by [Fe2(CO)4(κ2‐PNPR)(μ‐S(CH2)3S] (PNPR={Ph2PCH2}2NR,R=Me,Ph)

The behavior of [Fe₂(CO)₄(κ²‐PNP^R)(μ‐pdt)] (PNP^R=(Ph₂PCH₂)₂NR, R=Me ( 1 ), Ph ( 2 ); pdt=S(CH₂)₃S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP^R appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF₃SO₃H or CH₃SO₃H; the cation with a bridging hydride ligand, 1 μH⁺ (R=Me) or 2 μH⁺ (R=Ph) is obtained rapidly. Only 1 μH⁺ can be protonated at the nitrogen atom of the PNP chelate by HBF₄?Et₂O or CF₃SO₃H, which results in a positive shift of the proton reduction by approximately 0.15 V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η²‐H₂ species in the Fe^IFe^II state. When R=Ph, the bridging hydride cation 2 μH⁺ cannot be protonated at the amine function by HBF₄?Et₂O or CF₃SO₃H, and protonation at the N atom of the one‐electron reduced analogue is also less favored than that of a S atom of the partially de‐coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2 μH⁺ . The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 (k_obs≈4–7 s^?1) because of the slow intramolecular proton migration and H₂ release steps identified by the theoretical study.     

Interface‐Engineered Ni(OH)2/β‐like FeOOH Electrocatalysts for Highly Efficient and Stable Oxygen Evolution Reaction

Iron‐based (oxy)hydroxides are especially attractive electrocatalysts for the oxygen evolution reaction (OER) owing to their earth abundance, low cost, and nontoxicity. However, poor OER kinetics on the surface restricts the performance of the FeOOH electrocatalyst. Herein, a highly efficient and stable Ni(OH)₂/β‐like FeOOH electrocatalyst is obtained by facile electroactivation treatment. The activated Ni(OH)₂/β‐like FeOOH sample indicates an overpotential of 300 mV at 10 mA cm⁻² for the OER, and no clear current decay after 50 h of testing; this is comparable to the most efficient nickel‐ and cobalt‐based electrocatalysts on planar substrates. Furthermore, studies suggest that β‐like FeOOH plays a key role in remarkably enhancing the performance during the electroactivation process owing to its metastable tunnel structure with a lower barrier for interface diffusion of Ni²⁺ ions between the bilayer electrocatalyst. This study develops a new strategy to explore efficient and low‐cost electrocatalysts and deepens understanding of bilayer electrocatalysts for the OER.     

Synthesis,Characterization, and Highly Selective Ethylene Dimerization to 1‐Butene of [O−NX]Ni(II) Complexes

A series of nickel(II) complexes have been synthesized and characterized. Molecular structure analysis exhibits that a square planar geometry around nickel is adopted. Upon activation with MAO, these nickel(II) complexes are efficient in catalyzing the ethylene dimerization, providing 1‐butene with an activity of up to 1.4×10⁷ g/(mol·h·atm). The heteroatoms of the sidearm in the complexes were proved to have great impact on the activity and selectivity of 1‐butene.     

Triangular Nickel Complexes Derived from 2‐Pyridylcyanoxime: An Approach to the Magnetic Properties of the [Ni3(μ3‐OH){pyC(R)NO}3]2+ Core

A series of nickel complexes with nuclearity ranging from Ni₃ to Ni₆ have been obtained by treatment of a variety of nickel salts with the 2‐pyridylcyanoxime ligand. The reported compounds have as a common structural feature the triangular arrangement of nickel cations bridged by a central μ₃‐oxo/alkoxo ligand. These compounds are simultaneously the first nickel derivatives of the 2‐pyridylcyanoxime ligand and the first examples of isolated, μ₃‐O triangular pyridyloximate nickel complexes. Magnetic measurements reveal antiferromagnetic interactions promoted by the μ₃‐O and oximato superexchange pathways and comparison of the experimental structural and magnetic data with DFT calculations give an in‐depth explanation of the factors that determine the magnetic interaction in this kind of system.     

[FeFe] Hydrogenase: Protonation of {2Fe3S} Systems and Formation of Super‐reduced Hydride States

The synthesis and crystallographic characterization of a complex possessing a well‐defined {2Fe3S(μ‐H)} core gives access to a paramagnetic bridging hydride with retention of the core geometry. Chemistry of this 35‐electron species within the confines of a thin‐layer FTIR spectro‐electrochemistry cell provides evidence for a unprecedented super‐reduced Fe^I(μ‐H)Fe^I intermediate.     

Two tetranuclear zinc clusters, [Zn4(μ3‐OEt)2(μ2‐MalO)4Et2] and [Zn4(μ3‐GueO)2(μ2‐GueO)2(μ2‐MalO)2(MalO)2]·2C7H8, containing defective dicubane core geometries (MalOH is maltol and GueOH is guethol)

The zinc alkoxide molecules in di‐μ₃‐ethanolato‐diethyltetrakis(μ₂‐2‐methyl‐4‐oxo‐4H‐pyran‐3‐olato‐κ³O³,O⁴:O³)tetrazinc(II), [Zn₄(C₂H₅)₂(C₂H₅O)₂(C₆H₅O₃)₄], (I), and bis(μ₃‐2‐ethoxyphenolato‐κ⁴O¹,O²:O¹:O¹)bis(μ₂‐2‐ethoxyphenolato‐κ³O¹,O²:O¹)bis(μ₂‐2‐methyl‐4‐oxo‐4H‐pyran‐3‐olato‐κ³O³,O⁴:O³)bis(2‐methyl‐4‐oxo‐4H‐pyran‐3‐olato‐κ²O³,O⁴)tetrazinc(II) toluene disolvate, [Zn₄(C₆H₅O₃)₄(C₈H₉O₂)₄]·2C₇H₈, (II), lie on crystallographic centres of inversion. The asymmetric units of (I) and (II) contain half of the tetrameric unit and additionally one molecule of toluene for (II). The Zn^II atoms are four‐ and six‐coordinated in distorted tetrahedral and octahedral geometries for (I), and six‐coordinated in a distorted octahedral environment for (II). The Zn^II atoms in both compounds are arranged in a defect dicubane Zn₄O₆ core structure composed of two EtZnO₃ tetrahedra and ZnO₆ octahedra for (I), and of four ZnO₆ octahedra for (II), sharing common corners. The maltolate ligands exist mostly in a μ₂‐bridging mode, while the guetholate ligands prefer a higher coordination mode and act as μ₃‐ and μ₂‐bridges.     

Reversible Electrocatalytic Activity of Carbon‐Supported PtxNi1−x in Hydrogen Reactions

Hydrogen oxidation and evolution reactions (HOR and HER) are studied on Pt_xNi_1?x/C materials synthesized by the bromide anion exchange method. Physicochemical characterization shows that this surfactant‐free method enables the preparation of well‐dispersed and effective catalysts for the processes involved in the anode of H₂/O₂ fuel cells (HOR) and the cathode of water electrolyzers (HER). The Pt‐based materials are modified with different Ni contents to decrease the amount of costly precious metal in the electrode materials. These modified Pt‐based materials are found to be electroactive for both reactions without additional overpotential. Kinetic parameters such as the Tafel slope, exchange (j₀) and kinetic current densities, and the rate‐determining steps of the reaction mechanisms are determined for each Pt–Ni catalyst and compared to those obtained at the Pt/C surface in alkaline medium. The high j₀ values that are obtained indicate a probable contribution of the surface structure of the catalysts due to their roughness and the presence of oxygenated Ni species even at low potentials.     

A trinuclear Mo-Fe-Mo cluster compound [Et_4N] { [Me_2dtcMo-O(μ-S)_2]_2Fe} containing dialkyldithiocarbamate ligand

A trinuclear linear Mo-Fe-Mo dialkyldithiocarbamate complex [Et4N] { [ Me2dtcMoO (μ-S)2 ]2Fe} has been obtained and structurally characterized, which contains two Me2dtcMoO-(μ-S)2 units coordinated to a central tetrahedral Fe atom. A comparison of the structural parameters indicates the metal oxidation states of 2Mo(v) Fe(III). The 1H NMR shows chemical shifts of Me2dtc ligands at 5 10.14 and 8 9.40 with the intensity ratio of 1:1. The cyclic voltammogram displays a reversible couple at - 1.41 V/ - 1.36 V responsible for 1-/2-anions of the complex and an irreversible oxidation at 0.5 V, which seems to show the apparent lack of stability for its neutral species (Me2dtcMoOS2)2Fe.     

The Disproportionation of [Ni(tacn)]2+ in Ni2+ and [Ni(tacn)2]2+ Crystallographically Demonstrated (tacn=1,4,7‐Triazacyclononane)

From an EtOH/H₂O solution, 0.3 M each of Ni²⁺ and cyclic triamine tacn ( 2 ; tacn=1,4,7‐triazacyclononane), after 10 min refluxing and cooling at room temperature, copious and comparable amounts of blue crystals (containing the complex [Ni(tacn)(H₂O)₃]²⁺) and pink crystals (containing in the same cell both [Ni(H₂O)₆]²⁺ and [Ni(tacn)₂]²⁺) precipitated. This unusual behaviour is ascribed to the fact that at the refluxing temperature the three species are present at the equilibrium in similar concentrations, which are frozen on cooling, due to the inertness of the macrocyclic complexes [Ni(tacn)(H₂O)₃]²⁺ and [Ni(tacn)₂]²⁺.     

Poly[aqua(μ3‐benzene‐1,2‐dicarboxylato)bis(μ3‐hydroxido)bis(μ2‐isonicotinato)dierbium(III) monohydrate] and the thulium analogue

The two isomorphous lanthanide coordination polymers, {[Ln₂(C₆H₄NO₂)₂(C₈H₄O₄)(OH)₂(H₂O)]·H₂O}_n (Ln = Er and Tm), contain two crystallographically independent Ln ions which are both eight‐coordinated by O atoms, but with quite different coordination environments. In both crystal structures, adjacent Ln atoms are bridged by μ₃‐OH groups and carboxylate groups of isonicotinate and benzene‐1,2‐dicarboxylate ligands, forming infinite chains in which the Er...Er and Tm...Tm distances are in the ranges 3.622 (3)–3.894 (4) and 3.599 (7)–3.873 (1) Å, respectively. Adjacent chains are further connected through hydrogen bonds and π–π interactions into a three‐dimensional supramolecular framework.     

Poly[bis[aquaneodymium(III)]‐μ2‐oxalato‐di‐μ4‐succinato]

In the title compound, [Nd₂(C₄H₄O₄)₂(C₂O₄)(H₂O)₂]_n, the flexible succinate anion assumes the gauche conformation and bridges the nine‐coordinate Nd atoms to generate two‐dimensional layers parallel to (010). The coordination polymer layers are linked into a three‐dimensional framework by the rigid oxalate ligands. The oxalate ions are located on a center of inversion.     

Heterodinukleare Komplexe: Synthese und Kristallstrukturen von [RuRh(μ‐CO)(CO)4(μ‐PtBu2)(tBu2PH)], [RuRh(μ‐CO)(CO)3(μ‐PtBu2)(μ‐Ph2PCH2PPh2)] und [CoRh(CO)4(μ‐H)(μ‐PtBu2)(tBu2PH)]

Heterobinuclear Complexes: Synthesis and X‐ray Crystal Structures of [RuRh(μ‐CO)(CO)₄(μ‐P^tBu₂)(^tBu₂PH)], [RuRh(μ‐CO)(CO)₃(μ‐P^tBu₂)(μ‐Ph₂PCH₂PPh₂)], and [CoRh(CO)₄(μ‐H)(μ‐P^tBu₂)(^tBu₂PH)] [Ru₃Rh(CO)₇(μ₃‐H)(μ‐P^tBu₂)₂(^tBu₂PH)(μ‐Cl)₂] ( 2 ) yields by cluster degradation under CO pressure as main product the heterobinuclear complex [RuRh(μ‐CO)(CO)₄(μ‐P^tBu₂)(^tBu₂PH)] ( 4 ). The compound crystallizes in the orthorhombic space group Pcab with a = 15.6802(15), b = 28.953(3), c = 11.8419(19) Å and V = 5376.2(11) ų. The reaction of 4 with dppm (Ph₂PCH₂PPh₂) in THF at room temperature affords in good yields [RuRh(μ‐CO)(CO)₃(μ‐P^tBu₂)(μ‐dppm)] ( 7 ). 7 crystallizes in the triclinic space group P 1 with a = 9.7503(19), b = 13.399(3), c = 15.823(3) Å and V = 1854.6 ų. Moreover single crystals of [CoRh(CO)₄(μ‐H)(μ‐P^tBu₂)(^tBu₂PH)] ( 9 ) could be obtained and the single‐crystal X‐ray structure analysis revealed that 9 crystallizes in the monoclinic space group P2₁/a with a = 11.611(2), b = 13.333(2), c = 18.186(3) Å and V = 2693.0(8) ų.     

Poly[diaqua[μ4‐4‐(isonicotinamido)phthalato]nickel(II)] displaying an sra topology

In the title compound, [Ni(C₁₄H₈N₂O₅)(H₂O)₂]_n, the Ni^II cation is six‐coordinate with a slightly distorted octahedral coordination geometry and the 4‐(isonicotinamido)phthalate ligand links the Ni^II centres into a three‐dimensional structure with sra topology. The structure is also stabilized by N—H...O hydrogen bonding between the uncoordinated amide groups of the ligand and extensive O—H...O hydrogen bonding between the two coordinated water molecules. The magnetic and thermal stability properties of the title compound are also discussed.     

Aktivierung von Schwefelkohlenstoff an Trirutheniumclustern: Synthese und Kristallstruktur von [Ru3(CO)5(μ‐H)2(μ‐PCy2)(μ‐Ph2PCH2PPh2){μ‐η2‐PCy2C(S)}(μ3‐S)] und [Ru3(CO)5(CS)(μ‐H)(μ‐PtBu2)(μ‐PCy2)2(μ3‐S)]

Activation of Carbon Disulfide on Triruthenium Clusters: Synthesis and X‐Ray Crystal Structure Analysis of [Ru₃(CO)₅(μ‐H)₂(μ‐PCy₂)(μ‐Ph₂PCH₂PPh₂){μ‐η²‐PCy₂C(S)}(μ₃‐S)] and [Ru₃(CO)₅(CS)(μ‐H)(μ‐P^tBu₂)(μ‐PCy₂)₂(μ₃‐S)] [Ru₃(CO)₆(μ‐H)₂(μ‐PCy₂)₂(μ‐dppm)] ( 1 ) (dppm = Ph₂PCH₂PPh₂) reacts under mild conditions with CS₂ and yields by oxidative decarbonylation and insertion of CS into one phosphido bridge the opened 50 VE‐cluster [Ru₃(CO)₅(μ‐H)₂(μ‐PCy₂)(μ‐dppm){μ‐η²‐PCy₂C(S)}(μ₃‐S)] ( 2 ) with only two M–M bonds. The compound 2 crystallizes in the triclinic space group P 1 with a = 19.093(3), b = 12.2883(12), c = 20.098(3) Å; α = 84.65(3), β = 77.21(3), γ = 81.87(3)° and V = 2790.7(11) ų. The reaction of [Ru₃(CO)₇(μ‐H)(μ‐P^tBu₂)(μ‐PCy₂)₂] ( 3 ) with CS₂ in refluxing toluene affords the 50 VE‐cluster [Ru₃(CO)₅(CS)(μ‐H)(μ‐P^tBu₂)(μ‐PCy₂)₂(μ₃‐S)] ( 4 ). The compound cristallizes in the monoclinic space group P 2₁/a with a = 19.093(3), b = 12.2883(12), c = 20.098(3) Å; β = 104.223(16)° and V = 4570.9(10) ų. Although in the solid state structure one elongated Ru–Ru bond has been found the complex 4 can be considered by means of the ³¹P‐NMR data as an electron‐rich metal cluster.