Back-donation Research Articles

Adsorption and magnetic properties of Cu11MO12 (M = Cu, Ni and Co): Ab initio study

Abstract Hydrazine is toxic material that is recently used in wide scale and so we need to develop efficient sensing systems with high flexibility, and low capital cost for control recognition the adsorption of such materials. The structural stability, electronic and magnetic properties of nanocomposite of Cu11MO12 (M = Cu, Ni and Co) have been analyzed in the present work. By employing the density functional theory DFT based on ab initio approach, we studied the effect of hydrazine on the magnetic and electronic properties of Cu11MO12 (M = Cu, Ni and Co). The interaction between N2H4 molecules with the sorbent clusters is attributed to the donation – back donation mechanism. Ni and Co doping may lead to increase in electric conductivity of the CuO nanocluster. The total magnetic moments (μ) showed that the magnetic moment of our clusters depends on the spin of electrons in 3d orbital and there is increase in the magnetic moment with substitution of Ni and Co. There is no change in the total magnetic moment as a result of the adsorption of hydrazine for Cu12O12 and Cu11NiO12 clusters while the change occurred only in Cu11CoO12 cluster.

First Principles Study of Molecular O2 Adsorption on the PdO(101) Surface

Interactions of O2 with the PdO(101) surface were studied using spin-dependent density-functional theory (DFT) with both the PBE and the non-local hybrid HSE exchange–correlation functional. The adsorption energies are strongly overestimated (by 40–60 kJ/mol) with PBE, whereas HSE predicts adsorption energies that are within ~5 kJ/mol of values derived from temperature programmed desorption (TPD) experiments. A detailed partial density of states analysis indicates that the band gap between the PdO d-band center and the LUMO of O2 plays an important role in determining the adsorption strength. This gap is larger for the HSE functional and leads to a decrease in the back donation of the metal d-states to the O2 LUMO orbital resulting in weaker adsorption. Based on the DFT–HSE calculations, three adsorption minima are found to be stable. The most favored configuration, with an adsorption energy of −67 kJ/mol, consists of an O2 molecule lying flat and interacting with two coordinatively unsaturated Pd (Pdcus) surface atoms. The other two configurations have weaker adsorption energies of about −25 kJ/mol and bind to a single Pdcus atom with the O2 molecule oriented away from the surface. The HSE results can be correlated with the observed TPD spectra, which shows only one type of O2 configuration at low coverages with a subsequently lower temperature (more weakly bound) peak evolving at higher coverages associated with the singly coordinated O2 adsorption configurations that start to populate when two adjacent Pdcus sites start to become unavailable.

Infrared Photodisssociation Spectroscopy of Boron Carbonyl Cation Complexes

The boron carbonyl cation complexes B(CO)3+, B(CO)4+ and B2(CO)4+ are studied by infrared photodissociation spectroscopy and theoretical calculations. The B(CO)4+ ions are characterized to be very weakly bound complexes involving a B(CO)3+ core ion, which is predicted to have a planar D3h structure with the central boron retaining the most favorable 8-electron configuration. The B2(CO)4+ cation is determined to have a planar D2h structure involving a B−B one and half bond. The analysis of the B-CO interactions with the EDA-NOCV method indicates that the OC→B σ donation is stronger than the B→CO π back donation in both ions.

NATURE OF Mδ+···δ+C-Oδ-INTERACTIONS IN METAL CARBONYLS. AN ELECTRONIC STUDY BASED ON THE TOPOLOGY OF THE ELECTRON CHARGE DENSITY DISTRIBUTION AND ITS LAPLACIAN FUNCTION

Fil: Buralli, Gabriel Jesus. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura. Departamento de Ecologia de Anfibios; Argentina

Spectroscopic and computational investigations on the origin of charge transfer between included neutral guest molecules and a functionalized anionic layered host.

Layered double hydroxides (LDHs) or anionic clays are an important class of ion-exchange materials, well known for drug and gene delivery and several other applications including catalysis, bioactive nanocomposite, electroactive and photoactive materials. Their structure is based on positively charged brucite-like inorganic sheets with the interlamellar space being occupied by charge-compensating exchangeable anions. In spite of having a vast scope many of the applications of LDHs are restricted as their host-guest chemistry is limited to ion-exchange reactions. Recently we have shown for the first time that charge-transfer interactions can be used as a driving force for the insertion of neutral guest molecules (ortho- and para-chloranil) within the galleries of an Mg-Al LDH by forming a charge-transfer complex with aniline pre-intercalated as p-aminobenzoate anion. Here, we have performed quantum chemical calculations in combination with molecular dynamics simulations to elucidate the nature of interactions, arrangement and the evaluation of electronic and Raman spectral signatures of the chloranil charge-transfer complex included within the galleries of the Mg-Al LDH. The natural bond orbital (NBO) analysis has been used to understand the nature and origin of the unidirectional charge-transfer that lead to the unusual insertion of chloranil in the galleries of the Mg-Al LDH. The NBO analysis reveals that a considerable amount of electronic charge redistribution occurs from the p-aminobenzoate to the chloranil during latter's insertion within the LDH galleries with a very negligible amount of back donation. This work is expected to pave the way for understanding the host-guest chemistry and targeted and controlled delivery of poorly soluble drugs.

Structure and Bonding of an Intergrowth Phase Ca7Ag2+xGe7–x (x ≈ 2/3) Featuring a Zintl‐Type Polyanionic Chain

AbstractSingle crystals of a new ternary phase, Ca7Ag2+xGe7–x [x = 0.48(3)], were obtained from as side‐product of high‐temperature solid‐state reactions, and its crystal structure determined by X‐ray diffraction methods. Following the Zintl concept, the anionic substructure consists of a novel pentameric Zintl anion [Ge5]12– with C2v local symmetry, as well as [AgxGe2–x](6–3x)– units accounting for [Ge2]6– dimers and isolated Ge4– (and Ag+) species sharing the same atomic sites. DFT‐level band structure calculations were carried out on a hypothetical, fully ordered model (x = 0). We found that the electronic structure associated with the planar W‐shaped [Ge5]12– polyanions is more suited to optimize the structure's stability than the helical configuration of the isoelectronic [Se5]2–, in the context of incomplete charge transfer from the electropositive metal Ca. Thus, the antibonding states at the Fermi level that are centered on the two [Gen](2n+2)– oligomers can be depopulated by means of Ge‐to‐Ca electron back donation, strengthening at the same time the Ge–Ge bonds. These antibonding states also endow the system with substantial electronic flexibility, which may result in some phase width. Finally, plausible local ordering models of Ag/Ge mixing in [AgxGe2–x](6–3x)– units for x = 2/3, as expected from the Zintl concept, are briefly discussed within the “coloring problem” approach.

Encapsulation of sulfur, oxygen, and nitrogen mustards by cucurbiturils: a DFT study

A density functional theory analysis on the encapsulation of sulphur mustard (HD), oxygen mustard (OM), and nitrogen mustard (N1) by cucurbit[7]uril (CB[7]) molecule was carried out using the dispersion corrected B3LYP-D/6-311+G(d,p) method. The encapsulation of HD, OM and N1, have favorable interaction energy and are found to be functional dependent. Amongst the encapsulated molecules, N1@CB[7] has the least highest occupied molecular obitual- lowest unoccupied molecular orbital gap, which indicates that nitrogen mustard can be reversible stored inside CB[7]. Molecular electrostatic potential studies shows that charge transfer occurs between the host and guest molecule during the complexation process. Atoms-in-molecules analysis at the intermolecular bond critical points, have positive charge density, negative Laplacian and close to zero value of total energy density, indicating the depletion of electronic charge along the bond paths, which implies an electrostatic nature of bonding. The natural bond order analysis of N1@CB[7] complex with highest strongest second order perturbation energies are due to the donation of lone pair nitrogen of CB molecule to the guest molecule and the back donation of charge, leads to the high interaction energy. Non covalent index isosurface clearly show the existence of hydrogen bonding and van der Walls intermolecular interaction between the guest molecule and the host CB[7].

Application of scapula osteomyocutaneous flap in the repair of maxillary defect

Preliminary study on free scapula osteomyocutaneous flap to repair maxillary defect. Central maxillofacial soft and hard tissue defect after nasal sinus or oral tumor surgery was repaired with free scapual osteomyocutaneous flap in 4 patients to reconstruct their maxillofacial functions. The primary tumors included an ameloblastoma, a recurrent low-grade mucous epidermoid carcinoma a jaw sarcoma and a squamous cell carcinoma. All the 4 cases had good wound healing within 2 weeks after surgery, with no complications, could take in semifluid food after 3 weeks, and had clear language communication after 1 month. Three cases wore denture after 2 months and recovered maxillofacial contour and partial chewing function, and had no tumor recurrences with the follow-up of 37, 25 and 10 months respectively. One case of maxilla sarcomas had recurrence with invasion of parapharyngeal space and skull base and pulmonary metastasis 9 months after surgery, who gave up further treatment and died 1 year later. No obvious dysfunction occurred in shoulder and back donation sites and well blood supply in transplanted bones were showed with CT and bone scan. Scapula osteomyocutaneous flap has some advantages including reliable blood supply, hidden incision and little affect on the donation site, and it can apply with multiple tissues including bone, muscle, and skin for repair. This flap also has good shape adaptability and availability. So scapula osteomyocutaneous flap is a satisfactory method for the repair of facial maxillary complex defects. But some limitations exist in the flap, by which less amount of bone can be applied and more operation time is required due to the changes of patient's body position during surgery.

Rhodium(I) and Iridium(I) Complexes of the Conformationally Rigid IBioxMe4 Ligand: Computational and Experimental Studies of Unusually Tilted NHC Coordination Geometries

Computational methods have been used to analyze distorted coordination geometries in a coherent range of known and new rhodium(I) and iridium(I) complexes containing bioxazoline-based NHC ligands (IBiox). Such distortions are readily placed in context of the literature through measurement of the Cnt(NHC)–CNCN–M angle (ΘNHC; Cnt = ring centroid). On the basis of restricted potential energy calculations using cis-[M(IBioxMe4)(CO)2Cl] (M1; M = Rh, Ir), in-plane (yawing) tilting of the NHC was found to incur significantly steeper energetic penalties than orthogonal out-of-plane (pitching) movement, which is characterized by noticeably flat potential energy surfaces. Energy decomposition analysis (EDA) of the ground-state and pitched structures of M1 indicated only minor differences in bonding characteristics. In contrast, yawing of the NHC ligand is associated with a significant increase in Pauli repulsion (i.e., sterics) and reduction in M→NHC π back donation, but is counteracted by supplemental stabilizing bonding interactions only possible due to the closer proximity of the methyl substituents with the metal and ancillary ligands. Aided by this analysis, comparison with a range of carefully selected model systems and EDA, distorted coordination modes in trans-[M(IBioxMe4)2(COE)Cl] (M2; M = Rh, Ir) and [M(IBioxMe4)3]+ (M3; M = Rh, Ir) have been rationalized. Steric interactions were identified as the major contributing factor and are associated with a high degree of NHC pitching. In the case of Rh3, weak agostic interactions also contribute to the distortions, particularly with respect to NHC yawing, and are notable for increasing the bond dissociation energy of the distorted ligands. Supplementing the computational analysis, an analogue of the formally 14 VE Rh(I) species Rh3 bearing the cyclohexyl-functionalized IBiox6 ligand ([Rh(IBiox6)3]+, Rh3-Cy) was prepared and found to exhibit an exceptionally distorted NHC ligand (ΘNHC = 155.7(2)°) in the solid state.

The Triple‐Bond Metathesis of Aryldiazonium Salts: A Prospect for Dinitrogen Cleavage

AbstractThe {N2} unit of aryldiazonium salts undergoes unusually facile triple‐bond metathesis on treatment with molybdenum or tungsten alkylidyne ate complexes endowed with triphenylsilanolate ligands. The reaction transforms the alkylidyne unit into a nitrile and the aryldiazonium entity into an imido ligand on the metal center, as unambiguously confirmed by X‐ray structure analysis of two representative examples. A tungsten nitride ate complex is shown to react analogously. Since the bonding situation of an aryldiazonium salt is similar to that of metal complexes with end‐on‐bound dinitrogen, in which {N2}→M σ donation is dominant and electron back donation minimal, the metathesis described herein is thought to be a conceptually novel strategy toward dinitrogen cleavage devoid of any redox steps and, therefore, orthogonal to the established methods.

The Triple-Bond Metathesis of Aryldiazonium Salts: A Prospect for Dinitrogen Cleavage.

The {N2 } unit of aryldiazonium salts undergoes unusually facile triple-bond metathesis on treatment with molybdenum or tungsten alkylidyne ate complexes endowed with triphenylsilanolate ligands. The reaction transforms the alkylidyne unit into a nitrile and the aryldiazonium entity into an imido ligand on the metal center, as unambiguously confirmed by X-ray structure analysis of two representative examples. A tungsten nitride ate complex is shown to react analogously. Since the bonding situation of an aryldiazonium salt is similar to that of metal complexes with end-on-bound dinitrogen, in which {N2 }→M σ donation is dominant and electron back donation minimal, the metathesis described herein is thought to be a conceptually novel strategy toward dinitrogen cleavage devoid of any redox steps and, therefore, orthogonal to the established methods.

Adsorption states of typical intermediates on Ag/Al2O3 catalyst employed in the selective catalytic reduction of NOx by ethanol

The adsorption of ethanol and important intermediates onto Ag/Al2O3 catalyst employed in the selective catalytic reduction of NOx by ethanol was simulated by density functional theory. Considering the interaction between Ag metal and Al2O3 support, typical Ag–O–Al entities, i.e., Ag–O–Altetra and Ag–O–Alocta, (tetra = tetrahedral and octa = octahedral refer to the coordination sites of Al), were selected as potential adsorption sites on the surface of the catalyst. Ethanol, and enolic and isocyanate species were preferentially adsorbed and activated by Ag–O–Altetra entities rather than by Ag–O–Alocta entities. The strong Lewis acidity of Altetra in the Ag–O–Altetra entity was very important, enabling the entity to accept an electron via forward donation from either the C–O σ bond in ethanol or the N–C σ bond in the –NCO species. Moreover, the hybridization of the Ag and Al orbitals was critical for electron back donation from the Ag–O–Altetra entity to the C–C π bond in the enolic species or N–C π bond in the –NCO species. The significant activation of the N–C bond in –NCO on the Ag–O–Altetra sites facilitated cleavage of –NCO to form N2. Thus, we can conclude that the acidity of the Al site and the interaction between Ag and Al play key roles in the selective catalytic reduction of NOx by ethanol over Ag/Al2O3.

Adsorption and dissociation of H2S on Mo2C(001) surface-A first-principle study

The adsorption and decomposition reaction mechanisms of H2S on Mo2C(001) has been systematically studied using self-consistent periodic density functional theory. Results show that the molecular of H2S is adsorbed either on the Mo top site or bridge site. Mulliken population analysis and density of states for H2S/Mo-terminated Mo2C(001) adsorption system are examined to confirm the adsorption mechanism of H2S with the Mo2C(001) surface, which can involve the donation of charge from the “s lone pair electrons” that are LUMO orbitals into the surface and the back donation of electrons from the surface into the HOMO orbital. The optimal pathway for the dissociation of H2S on the Mo2C(001) surface can be H2Stop→SHfcc+Hfcc→Sfcc+Hfcc+Hfcc. The first step is the rate-determining step because it has the smallest rate constant among the possible reactions pathways.

Inter-ligand azo (N=N) unit formation and stabilization of a Co(II)-diradical complex via metal-to-ligand dπ-pπ* back donation: synthesis, characterization, and theoretical study.

An azide (-N3) group attached at the -ortho carbon atom to the aniline moiety of 2-anilino-4,6-di-tert-butylphenol formed a diradical-containing Co(II) complex via inter-ligand azo (N=N) bond formation. Metal-to-ligand (azo), dπ-to-pπ* back donation stabilized the metal in its lower oxidation state.

Room Temperature Hydrogen Physisorption on Exposed Metals in A Highly Cross‐Linked Organo‐Iron Complex

Room Temperature Hydrogen Physisorption on Exposed Metals in A Highly Cross‐Linked Organo‐Iron Complex

Changes in serum levels of purines in an experimental infection by Leptospira interrogans serovar Icterohaemorrhagiae

The aim of this study was to measure the levels of purines in serum of rats experimentally infected with Leptospira interrogans serovar Icterohaemorrhagiae. For this purpose, 24 adult male Wistar rats were divided into two groups: A, not infected (subgroups A1 and A2), and B, infected (subgroups B1 and B2), which were intraperitoneally inoculated (day 0) with 2 × 108 leptospires/animal. Blood samples were collected on days 15 (A1 and B1) and 30 PI (A2 and B2) for analysis of purine levels in serum (adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), adenosine, inosine, hypoxanthine, xanthine, and uric acid). The levels of ATP, AMP, adenosine, and xanthine increased (P < 0.015), while a reduction (P < 0.015) in the concentration of ADP and inosine occurred at day 15 PI. On day 30 PI, ATP, ADP, adenosine, and uric acid significantly increased (P < 0.015), while xanthine level was reduced (P < 0.015). The correlation among the infection and purine levels lead us to suggest the purinergic system as a compensatory mechanism during the leptospirosis infection, mainly due to the actions of ATP, which usually is involved in a pro-inflammatory response, followed by a protective action of ADP and adenosine on the clotting events, along with a protective cellular damage caused by the infection.

DFT study of CO oxidation over Au/TiO2(1 1 0): The extent of the reactive perimeter zone

O2 adsorption and CO oxidation on a Au/rutile TiO2(110) catalyst have been examined by DFT in order to define the extent of the reactive perimeter zone. O2 is found to adsorb on the fivefold coordinated Ti sites that are away from the perimeter as well as on those next to the perimeter. Both O2 show similar reactivity toward a gaseous CO. CO oxidation still occurs predominantly at the perimeter because O2 adsorption is strongest at the perimeter Ti site and because CO is activated on Au through back donation.

Vanadium Sandwich Complexes with Boroxine and Boronyl Boroxine Ligands

AbstractA DFT investigation on half‐sandwich‐type C3v B3O3X3V, full‐sandwich‐type D3d [B3O3X3]2V, and triple‐decker complexes [B3O3X3]3V2 (X = H, BO) containing B3O3H3 or B3O3(BO)3 ligands were performed. Both B3O3H3 and B3O3(BO)3 units serve as robust inorganic ligands in B3O3X3V, [B3O3X3]2V, and [B3O3X3]3V2 complex series. Effective d–π coordination interactions between the partially filled 3d orbitals of the transition‐metal center and the delocalized π orbitals of the B3O3X3 ligands maintain the stabilities of the complexes. The largest contributions to the orbital interactions in the B3O3X3V, [B3O3X3]2V, and [B3O3X3]3V2 complexes come from the V → B3O3X3 δ back donation. The thermodynamic stabilities and magnetic properties of these complexes were also investigated. These magnetic complexes were found to be particularly stable with respect to their reaction energy. The sandwich structural pattern developed in this work expands the structural domain of transition‐metal complexes by introducing inorganic B3O3H3 and B3O3(BO)3 into traditional sandwich‐type structures, and this pattern may be extended to [B3O3X3]nVn–1 sandwiches (n ≥ 4), which could act as linear magnetic wires.

Structure of a Reactive Gold Carbenoid

A formal gold-for-chromium transmetalation allowed the gold carbenoid species [Cy3 PAuCAr2 ]NTf2 (11) (Ar=pMeOC6 H4 -) to be obtained in crystalline form. The structure in the solid state suggests that there is only little back donation of electron density from gold to the carbene center of 11 and hence very modest AuC double-bond character; rather, it is the organic ligand framework that is responsible for stabilizing this species by resonance delocalization of the accumulated positive charge. Because 11 is capable of cyclopropanating p-methoxystyrene even at low temperature, the discussion of its structure is deemed relevant for a better understanding of the mechanisms of π-acid catalysis in general.

Structure of a Reactive Gold Carbenoid

AbstractA formal gold‐for‐chromium transmetalation allowed the gold carbenoid species [Cy3PAuCAr2]NTf2 (11) (Ar=pMeOC6H4‐) to be obtained in crystalline form. The structure in the solid state suggests that there is only little back donation of electron density from gold to the carbene center of 11 and hence very modest AuC double‐bond character; rather, it is the organic ligand framework that is responsible for stabilizing this species by resonance delocalization of the accumulated positive charge. Because 11 is capable of cyclopropanating p‐methoxystyrene even at low temperature, the discussion of its structure is deemed relevant for a better understanding of the mechanisms of π‐acid catalysis in general.