End-on Mode Research Articles

Unveiling O2 adsorption on non-metallic active site for selective photocatalytic H2O2 production

Photocatalytic oxygen reduction reaction (ORR) offers a promising pathway for sustainable hydrogen peroxide (H2O2) production but faces challenges in developing catalysts with good ORR selectivity. Herein, we report that tailoring O2 adsorption on non-metallic active sites can optimize ORR selectivity. This concept is demonstrated on three carbon nitrides with different atomic configurations: polymeric carbon nitride (PCN), lithium-poly triazine imide (Li-PTI), and sodium-poly heptazine imide (Na-PHI). Na-PHI emerges as a strong candidate for H2O2 production due to the end-on adsorption mode and suitable adsorption strength with O2. Synthesized Na-PHI, PCN, and Li-PTI are characterized, with Na-PHI showing superior light absorption, charge carrier separation, and remarkable selectivity (92 %) for two-electron ORR. Consequently, Na-PHI achieves a high H2O2 generation rate of 3.48 mmol g−1 h−1, surpassing Li-PTI and PCN by 9.2 and 33 times, respectively. This study underscores the importance of O2 adsorption on non-metallic active sites for selective photocatalytic H2O2 generation.

Si-C atomic line achieving efficient electrocatalytic nitrogen reduction reactions

In this study, the concept of a Si-C atomic line (SCAL) featuring fully exposed atomic sites is introduced for the first time, and the SCAL serves as a highly efficient electrocatalyst for nitrogen reduction reactions (NRR). Thanks to the strong binding strength of the Si-C bonds (polar covalent bonds), the SCAL exhibits exceptional structural stability at 298.15 K. With a band gap of 1.86 eV characterized by a semiconductor, SCAL exhibits relatively high conductivity which is advantageous for electrocatalytic processes. N2 is adsorbed on the C sites in an end-on mode due to the most negative adsorption energy (–0.39 eV), and the nature of adsorption is s-p orbital hybridization. Based on the end-on N2 adsorption, the entire NRR pathway is simulated and shows a relatively low energy barrier of 0.50 eV, which is relatively low compared to reported metal-free NRR electrocatalysts. The charge transfer mechanism reveals that the active sites (C atoms) are responsible for charge transfer, while other parts of SCAL act as storage warehouses for charge. Moreover, SCAL demonstrates a preference for NRR over hydrogen evolution reaction (HER), underscoring its excellent electrocatalytic selectivity. This study opens new avenues for designing high-performance catalysts.

Exploring hydrogen binding and activation on transition metal-modified circumcoronene

AbstractGraphene-based materials modified with transition metals, and their potential utilization as hydrogen storage devices, are extensively studied in the last decades. Despite this widespread interest, a comprehensive understanding of the intricate interplay between graphene-based transition metal systems and H2 molecules remains incomplete. Beyond fundamental H2 adsorption, the activation of H2 molecule, crucial for catalytic reactions and hydrogenation processes, may occur on the transition metal center. In this study, binding modes of H2 molecules on the circumcoronene (CC) decorated with Cr or Fe atoms are investigated using the DFT methods. Side-on (η2-dihydrogen bond), end-on and dissociation modes of H2 binding are explored for high (HS) and low (LS) spin states. Spin state energetics, reaction energies, QTAIM and DOS analysis are considered. Our findings revealed that CC decorated with Cr (CC-Cr) emerges as a promising material for H2 storage, with the capacity to store up to three H2 molecules on a single Cr atom. End-on interaction in HS is preferred for the first two H2 molecules bound to CC-Cr, while the side-on LS is favored for three H2 molecules. In contrast, CC decorated with Fe (CC-Fe) demonstrates the capability to activate H2 through H–H bond cleavage, a process unaffected by the presence of other H2 molecules in the vicinity of the Fe atom, exclusively favoring the HS state. In summary, our study sheds light on the intriguing binding and activation properties of H2 molecules on graphene-based transition metal systems, offering valuable insights into their potential applications in hydrogen storage and catalysis. Graphical abstract

Selective Adsorption of Oxygen from Humid Air in a Metal-Organic Framework with Trigonal Pyramidal Copper(I) Sites.

High or enriched-purity O2 is used in numerous industries and is predominantly produced from the cryogenic distillation of air, an extremely capital- and energy-intensive process. There is significant interest in the development of new approaches for O2-selective air separations, including the use of metal-organic frameworks featuring coordinatively unsaturated metal sites that can selectively bind O2 over N2 via electron transfer. However, most of these materials exhibit appreciable and/or reversible O2 uptake only at low temperatures, and their open metal sites are also potential strong binding sites for the water present in air. Here, we study the framework CuI-MFU-4l (CuxZn5-xCl4-x(btdd)3; H2btdd = bis(1H-1,2,3-triazolo[4,5-b],[4',5'-i])dibenzo[1,4]dioxin), which binds O2 reversibly at ambient temperature. We develop an optimized synthesis for the material to access a high density of trigonal pyramidal CuI sites, and we show that this material reversibly captures O2 from air at 25 °C, even in the presence of water. When exposed to air up to 100% relative humidity, CuI-MFU-4l retains a constant O2 capacity over the course of repeated cycling under dynamic breakthrough conditions. While this material simultaneously adsorbs N2, differences in O2 and N2 desorption kinetics allow for the isolation of high-purity O2 (>99%) under relatively mild regeneration conditions. Spectroscopic, magnetic, and computational analyses reveal that O2 binds to the copper(I) sites to form copper(II)-superoxide moieties that exhibit temperature-dependent side-on and end-on binding modes. Overall, these results suggest that CuI-MFU-4l is a promising material for the separation of O2 from ambient air, even without dehumidification.

Insights into Glyphosate Adsorption in Aqueous Solutions Using Zn-Al Layered Double Oxide

AbstractContamination of surface and groundwater with glyphosate, used widely on crops to control weeds, can cause severe environmental damage. Processes for glyphosate removal from water bodies have been developed, but few are effective and all are expensive. This objective of the present study was to investigate the use of a layered double oxide as a potentially effective and inexpensive material to remove glyphosate from water. Equilibrium, kinetics, and adsorption mechanisms were evaluated, in addition to the effects of competing anions and temperature on glyphosate adsorption. Up to 95% of glyphosate was removed from a synthetic solution in 50 min by Zn2Al-LDO (layered double oxide in Zn/Al ratio of 2:1) at pH 10. The adsorption isotherms were type L and the Langmuir model best fitted the experimental data, with a qmax value of 191.96 μg mg–1 at 25°C. The XRD pattern did not support the hypothesis of intercalation of glyphosate anions, whereas Fourier-transform infrared and solid-state 13C and 31P magic angle spinning nuclear magnetic resonance confirmed the adsorption of glyphosate anions on the Zn2Al-LDO surface, through carboxylate and phosphonate moiety interactions with end-on and side-on modes. The degree of removal of glyphosate increased with increasing temperature and decreased with increasing concentration of competing anions, with carbonate anions having the most prominent effect on the inhibition of glyphosate adsorption. The adsorption kinetics fitted a pseudo-first order law. Moreover, the intraparticle diffusion model suggested that the adsorption process depends on the formation and thickness of the film at the solution/solid interface.

Surface oxygen vacancy-dependent molecular oxygen activation for propane combustion over α-MnO2

Oxygen vacancies (OV), as the sites of molecular oxygen adsorption and activation, play an important role in the catalytic combustion process of volatile organic compounds (VOCs). Revealing the relationship between OV concentration and molecular oxygen activation behavior is of significance to construct the efficient catalysts. Herein, α-MnO2 with different OV concentrations was prepared to investigate the molecular oxygen activation for C3H8 combustion. It is disclosed that the enhanced OV concentration in α-MnO2 induced the reconfiguration of surface metal atoms, resulting in the transformation of oxygen activation configuration from end-on mode to side-on mode. Oxygen molecules in side-on mode possessed more localized electron density and weaker coordination bond strength with surrounding Mn atoms, which were more favorable to adsorb C3H8 molecules and activate C-H bond for the improved combustion performance. This work provides a new understanding to reveal that the increased OV concentration contributes to more efficient VOCs combustion.

Rational Design of Heterogeneous Dual-Atom Catalysts for CO2 Electroreduction Reactions

One of the strategies to mitigate the concentration of CO2 in the atmosphere and reduce the global warming effect is to capture CO2 and convert it to synthetic fuels and fine chemicals. Although CO2 is structurally and chemically stable, the electrochemical transformation has attracted much attention because it offers mild reaction conditions regarding temperature, pressure, and process controllability. Among various electrocatalysts, dual-atom catalysts (DACs) have been extensively developed in the past few years due to their unique features for the electrochemical reactions of small molecules. The catalytic activity of DACs in the electrochemical CO2 reduction reaction (eCO2RR) has surpassed single-atom catalysts (SACs) by providing a higher metal loading, two active sites (cf. one active site for SACs), a synergistic effect of adjacent metal atoms, the possibility of tuning the electronic state (adjusting the d-band center), and more possible configuration modes (side-on and side-bridge) for adsorption of CO2 (cf. only end-on and end-bridge modes for SACs). As a result, both higher reactivity and selectivity in eCO2RR can be achieved by breaking scaling relationships with more possible interactions between intermediates and active sites. This review highlights and discusses the recent progress in applying homo- and heteronuclear DACs for eCO2RR focusing on the synthesis, characterization, and electrochemical catalytic performance.

Stabilization of Dinuclear Rhodium and Iridium Clusters on Layered Titanate and Niobate Supports.

Atomically dispersed organometallic clusters can provide well-defined nuclearity of active sites for both fundamental studies as well as new regimes of activity and selectivity in chemical transformations. More recently, dinuclear clusters adsorbed onto solid surfaces have shown novel catalytic properties resulting from the synergistic effect of two metal centers to anchor different reactant species. Difficulty in synthesizing, stabilizing, and characterizing isolated atoms and clusters without agglomeration challenges allocating catalytic performance to atomic structure. Here, we explore the stability of dinuclear rhodium and iridium clusters adsorbed onto layered titanate and niobate supports using molecular precursors. Both systems maintain their nuclearity when characterized using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Statistical analysis of HAADF-STEM images revealed that rhodium and iridium dimers had mean cluster-to-cluster distances very similar to what is expected from a random distribution of atoms over a large area, indicating that they are dispersed without aggregation. The stability of dinuclear rhodium clusters supported on titanate nanosheets was also investigated by X-ray absorption fine structure (EXAFS), DRIFTS, and first-principles calculations. Both X-ray absorption spectroscopy and HAADF-STEM simulations, guided by density functional theory (DFT)-optimized structure models, suggested that rhodium dimers adsorb onto the nanosheets in an end-on binding mode that is stable up to 100 °C under reducing conditions. This study highlights that crystalline nanosheets derived from layered metal oxides can be used as model supports to selectively stabilize dinuclear clusters, which could have implications for heterogeneous catalysis.

Theoretical prediction on stability, electronic and activity properties of single-atom catalysts anchored graphene and boron phosphide heterostructures

Introduction of graphene-like heterostructures supported single-atom catalysts (SACs) has been considered as a promising strategy for generating sustainable energy sources. By using first-principles calculation, different kinds of single transition metal (TM = Mn, Fe, Co and Ni) atoms anchored boron phosphide (BP-TM) and the effects of added graphene substrate on its electronic property and sensitivity toward the gas reactants are comparably investigated. The graphene support can provide the transferred electron to BP sheet and then regulate the adsorption strength and electronic structure of TM atoms anchored systems (BP-gra-TM). Besides, the adsorption of N2 molecule (parallel and end-on modes) on BP-gra-TM (including pristine and single vacancy (SV) within BP, i.e., BP-gra-SV-TM) are more stable than those on BP-TM and BP-SV-TM sheets, and then induce the change in electronic and magnetic properties of supported systems. Furthermore, the potential catalytic performances of four reactive substrates (BP-TM, BP-gra-TM, BP-SV-TM and BP-gra-SV-TM) are systematically explored for nitrogen reduction reaction (NRR). It is found that the NRR processes on BP-gra-Mn via enzymatic pathways and BP-gra-Fe via distal mechanism have lower limiting potential (0.52 V and 0.63 V) than other ones, indicating that the introduction of graphene can improve the surface activity of BP-TM sheets, which would provide useful guidance to design two-dimensional heterostructure-based SACs with high activity, efficiency and selectivity for the NRR.

Graphyne supported Co13, Fe13 and Ni13 nano-cluster as efficient electrocatalysts for nitrogen reduction reaction: A first principles study

A systematic first principles study is carried out to probe into the activity of graphyne supported Co13, Fe13 and Ni13 nano-clusters (NCs) towards the reduction of nitrogen (N2) into ammonia (NH3). Graphyne is found to highly stabilize the metal nano-clusters on its large pores through an exothermic chemisorption process. Adsorption of N2 on the graphyne supported NCs are detected to be highly exothermic in both end-on and side-on mode configurations. N2 becomes more activated via a higher amount of N-N bond stretching when adsorbed in side-on configuration. The activation of the N-N bond is shown to be directly proportional to the amount of charge transfer to the adsorbed N2 molecule. Thorough analysis of the nitrogen reduction reaction (NRR) on each graphyne supported metal NC reveals that NRR starting from side-on mode N2 adsorbed configuration prefers the enzymatic pathway though other pathways are possible at the cost of relatively higher overpotential. Only the distal pathway is energetically favoured following the end-on mode N2 adsorbed configuration. Graphyne supported Co13, Fe13 and Ni13 NCs are shown to carry out NRR with substantially low overpotential values of 0.24 V, 0.28 V and 0.37 V respectively. The active sites located far from the graphyne substrate are found to be more selective towards NRR with low overpotential than hydrogen evolution reaction. The NCs maintain their structural stability on the graphyne surface throughout the whole reaction process via different pathways showing that graphyne is a potentially very promising substrate material to stabilize the NC electrocatalysts and to improve their electrocatalytic activities towards NRR.

Prediction of single-boron anchored on MXene catalysts for high-efficient electrocatalytic nitrogen reduction reaction

The design of efficient catalysts plays an important role in the development of electrochemical nitrogen reduction reaction (NRR). 2D materials MXene can be used as promising catalyst substrates in NRR due to their superior chemical stability and conductivity. Here, using density functional theory calculations, 9 kinds of single-atom catalysts (SACs) B@M3C2O2-x (M = Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W) were constructed by anchoring electron-deficient non-metal boron atom on M3C2O2-x with one terminal-O vacancy. All SACs have good thermodynamic and electrochemical stability. The strong acceptor-donor interaction between B atom and N2 molecule leads to the activation of N2, thus promoting NRR. We adopted the screening strategies, including comparing the free energy of N2 adsorption, the free energy changes for the first and last electrochemical steps of NRR, and the selectivity of hydrogen evolution reaction (HER). Finally, five candidate catalysts (B@V3C2O2-x, B@Cr3C2O2-x, B@Nb3C2O2-x, B@Mo3C2O2-x and B@W3C2O2-x) were screened out. Starting from the end-on adsorption mode of N2, NRR proceeds through a mixed mechanism on each SAC. Our results show that these five SACs have excellent catalytic performance with the limiting potentials ranging from -0.32 to -0.48 V, which may be promising NRR electrocatalysts.

Concomitant dimorphism in poly[di-μ-azido-(5,5'-dimethyl-2,2'-bipyridine)iron(II)

The title metal-organic polymer, catena-poly[[(5,5'-dimethyl-2,2'-bipyridine-κ2N,N')iron(II)]-di-μ-azido-κ2N1:N3-[(5,5'-dimethyl-2,2'-bipyridine-κ2N,N')iron(II)]-di-μ-azido-κ2N1:N1], [Fe(N3)2(C12H12N2)]n, features alternating μ-1,1 (end-on mode of coordination) and μ-1,3 (end-to-end mode of coordination) double azide bridges, forming chains running in the [100] direction. The octahedral coordination geometry around the FeII centre is completed by a bidentate 5,5'-dimethyl-2,2'-bipyridine ligand. Two polymorphs for this compound were obtained from the crude reaction product, the first in the space group P-1 and the other in P21/c. The molecular and crystal structures are very similar for both forms, the main difference being that the eight-membered Fe(μ-1,3-N3)2Fe metallacycle formed with end-to-end azide ligands has a nearly flat conformation in the triclinic form and a chair conformation in the monoclinic form. In spite of this geometric difference, both forms have the same density, the same packing index and similar arrangements of the one-dimensional chains in the crystal. As a consequence, they also share very similar Hirshfeld surfaces and fingerprint plots. However, a density functional theory (DFT) computational study showed that the monoclinic form is more stable than the triclinic form by ca 30.5 kJ mol-1.

Efficient removal of glyphosate from aqueous solutions by adsorption on Mg-Al-layered double oxides: thermodynamic, kinetic, and mechanistic investigation.

Up to 90% of glyphosate was removed in 40 min by a 2:1 Mg2Al-layered double oxide (LDO) at pH 10, and the adsorption kinetics fitted a pseudo-second-order law. The adsorption isotherms were type L, and the Langmuir model best fitted the experimental data, with qmax of 158.22 μg/mg at 25 °C. The intraparticle diffusion model suggested that the adsorption process is dependent on the thickness and formation of the film at the solution/solid interface. The XRD results excluded the intercalation of glyphosate anions, and FTIR along with solid-state 13C and 31P MAS NMR confirmed that the glyphosate anions interact through the carboxylate and/or phosphonate moieties, both in end-on and side-on modes to the LDO surface. Glyphosate removal was also investigated in the presence of different anionic species, and simultaneous adsorption showed that carbonate and phosphate ions strongly influence glyphosate removal.

Nitrogen reduction to ammonia triggered by heterobimetallic uranium-group 10 metal complexes of phosphinoaryl oxides: A relativistic DFT study

The well-established Haber-Bosch process for ammonia synthesis suffers from extremely high energy consumption due to severe conditions of temperature and pressure, urging the need for active and case-specific catalysts. Herein, heterobimetallic uranium-transition metal complexes of phosphinoaryl oxide ligands, labelled as [IU-TM]z (TM = Ni, Pd and Pt; z = -2 ∼ +2), were comprehensively studied for N2 fixation and NH3 production by relativistic density functional theory. Of them, the neutral analogues were experimentally synthesized. It is shown that the U-Ni complexes are able to bind N2 in the end-on and side-on modes, but the Pd and Pt ones fail to adsorb the small molecule. Interestingly, the one-electron reduced species [IU-Ni]–, electrochemically accessible in experiment, gives off extraordinarily low free energies (-2.30 eV) for the end-on attachment. The first proton-electron pair addition is also exothermic (-0.94 eV) relative to the initial step. These steps enhance the selectivity for ammonia synthesis of our bimetallic system. With constantly updating the system using H+ + e– pairs, the nitrogen reduction reaction (NRR) follows a thermodynamically favored pathway regardless of taking alternating or distal mechanisms. Calculated electrochemical potentials and overpotentials offer the uranium-nickel complex potential application in NRR.

Hydrogenation of pyridine and hydrogenolysis of piperidine over γ-Mo2N catalyst: a DFT study

Increasing demands on producing environmentally friendly products are becoming a driving force for designing highly active catalysts. Thus, surfaces that efficiently catalyse the nitrogen reduction reactions are greatly sought in moderating air-pollutant emissions. This contribution aims to computationally investigate the hydrodenitrogenation (HDN) networks of pyridine over the γ-Mo2N(111) surface using a density functional theory (DFT) approach. Various adsorption configurations have been considered for the molecularly adsorbed pyridine. Findings indicate that pyridine can be adsorbed via side-on and end-on modes in six geometries in which one adsorption site is revealed to have the lowest adsorption energy (–45.3 kcal/mol). Over a nitrogen hollow site adsorption site, initial HDN steps proceed by the stepwise hydrogenation of pyridine into piperidine followed by the Langmuir–Hinshelwood mechanism. The obtained findings are the first to theoretically model the hydrogenation pathways of pyridine to form piperidine and then the hydrogenolysis of piperidine producing C5H12 and NH3 over metal nitride. These paved the way for further investigations to better understanding such an important nitrogen removal reactions.

Lithium-Assisted Dinitrogen Reduction Mediated by Nb2LiNO1-4- Cluster Anions: Electron Donors or Structural Units.

Alkali atoms are usually used as promoters to significantly increase the catalytic activity of transition-metal catalysts in a wide range of reactions such as dinitrogen conversion reactions. However, the role of alkali metal atoms remains controversial. Herein, a series of quaternary cluster anions containing lithium atoms Nb2LiNO1-4- have been synthesized and reacted with N2 at room temperature. The detailed experimental and theoretical investigations indicate that Nb2LiNO- is capable to cleave the N≡N bond and the Li atoms in Nb2LiNO1,2- act as electron donors in the N2 reduction reaction. With the increase in the number of oxygen atoms, the reactivity toward N2 is reduced from adsorption via a side-on end-on mode in Nb2LiNO2- to the inertness of Nb2LiNO4-. In Nb2LiNO3,4- anions, the Li atoms are bonded with oxygen atoms, acting as structural units to stabilize structures. Therefore, the roles of alkali atoms are able to change with different chemical environments of active sites. For the first time, we reveal how the number of ligands (oxygen atoms herein) can be used to finely regulate the reactivity toward N2.

Structural and spectroscopic studies of spontaneously formed crystalline Eu(iii)-aliphatic dicarboxylates at room temperature.

Complexation of actinides and lanthanides with carboxylic organic ligands is a critical issue affecting radionuclide migration from deep geological disposal systems of spent nuclear fuel. A series of Eu(iii)–aliphatic dicarboxylate compounds, as chemical analogs of radioactive Am(iii) species, Eu2(Ox)3(H2O)6, Eu2(Mal)3(H2O)6, and Eu2(Suc)3(H2O)2, were synthesized and characterized using X-ray crystallography and time-resolved laser fluorescence spectroscopy to examine the ligand-dependent binding modes and the corresponding changes in spectroscopic properties. Powder X-ray crystallography results confirmed that all of the compounds presented a crystalline polymer structure with a trigonal prism square-face tricapped polyhedron geometry centered on Eu(iii) in a nine-coordinate environment involving nine oxygen atoms. This study captures the transition of the coordination modes of aliphatic dicarboxylate ligands from side-on to end-on binding as the carbon chain length increases. This transition is illustrated in malonate bindings involving a combination of side-on and end-on modes. Strongly enhanced luminescence, especially for the hypersensitive peak, indicates a low site symmetry in the formation of solid compounds. The number of remaining bound water molecules was estimated from the resultant increased luminescence lifetimes, which were in good agreement with crystal structures. The excitation–emission matrix spectra of these crystalline polymers suggest that Ox ligands promote the sensitized luminescence of Eu(iii), especially in the UV region. In the case of Mal and Suc ligands, charge transfer occurs in the opposite direction from Eu(iii) to the ligands under UV excitation, resulting in weaker luminescence.

Dual Iron Sites in Activation of N2 by Iron-Sulfur Cluster Anions Fe5S2- and Fe5S3.

Inspired by the fact that the active centers of natural nitrogenases are polynuclear iron-sulfur clusters, the reactivity of isolated iron-sulfur clusters toward N2 has received considerable attention to gain fundamental insights into the activation of the N≡N triple bond. Herein, a series of gas-phase iron-sulfur cluster anions FexSy- (x = 1-8, y = 0-x) were prepared and their reactivities toward N2 were investigated systematically by mass spectrometry. Among the 44 investigated clusters, only Fe5S2- and Fe5S3- showed superior reactivity toward N2. Theoretical results revealed that N2 binds molecularly to the iron sites of Fe5S2,3- in a common end-on coordination mode with an unprecedented back-donation interaction from the localized d-d bonding orbitals of Fe-Fe sites to the π* antibonding orbitals of N2. This is the first example to disclose the significant contribution of the dual metal sites rather than the single metal atom to N2 adsorption in the prevalent end-on binding mode.

Decomposition of nitrous oxide in hydrated cobalt(I) clusters: a theoretical insight into the mechanistic roles of ligand-binding modes.

Hydrated cobalt(i) cluster ions, [Co(H2O)n]+, can decompose the inert nitrous oxide molecule, N2O. Density functional theory suggests that N2O can anchor to Co+ of [Co(N2O)(H2O)n]+ through either O end-on (η1-OL) or N end-on (η1-NL) coordinate mode. The latter is thermodynamically more favorable resulting from a subtle π backdonation from Co+ to N2O. N2O decomposition involves two major processes: (1) redox reaction and (2) N-O bond dissociation. The initial activation of N2O through an electron transfer from Co+ to N2O yields anionic N2O-, which binds to the metal center of [Co2+(N2O-)(H2O)n] also through either O end-on (η1-O) or N end-on (η1-N) mode and is stabilized by water molecules through hydrogen bonding. From η1-O, subsequent N-O bond dissociation to liberate N2, producing [CoO(H2O)n]+, is straightforward via a mechanism that is commonplace for typical metal-catalyzed N2O decompositions. Unexpectedly, the N-O bond dissociation directly from η1-N is also possible and eliminates both N2 and OH, explaining the formation of [CoOH(H2O)n]+ as observed in a previous experimental study. Interestingly, formation of [CoO(H2O)n]+ is kinetically controlled by the initial redox process between Co+ and the O-bound N2O, the activation barriers of which in large water clusters (n ≥ 14) are higher than that of the unexpected N-O bond dissociation from the N-bound structure forming [CoOH(H2O)n]+. This theoretical discovery implies that in the present of water molecules, the metal-catalyzed N2O decomposition starting from an O-bound metal complex is not mandatory.

Synthesis and crystal structure of a phenolato, chlorido and end-on azido-cobridged tetranuclear copper(II) complex derived from 2-[(2-dimethylaminoethylimino)methyl]-4-methylphenol

A novel phenolato-, chlorido- and end-on azido-cobridged tetranuclear copper(II) complex, [Cu4(daemp)2Cl2(μ-Cl)2(μ1,1-N3)2(MeOH)2] (Hdaemp = 2-[(2-dimethylaminoethylimino)methyl]-4-methylphenol), was prepared and characterized by elemental analyses, IR and UV-Vis spectra, and single crystal X-ray diffraction study. The Schiff base ligands coordinate to the Cu atoms through phenolate O, imino N and amino N atoms. The adjacent Cu···Cu distances are 3.169(2) and 3.063(2) Å. Each Cu atom is in a square pyramidal coordination. The azido ligands link two Cu atoms with end-on bridging mode. There are two coordination modes for the Cl ligands, viz. terminal and bridging. In the crystal structure, the complex molecules are stack along the b axis.