Photocatalytic conversion of CO2 to CO by Ru(II) and Os(II) octahedral complexes: a DFT/TDDFT study.

The reaction mechanisms of the photocatalytic reduction of CO2 to CO catalyzed by [(en)M(CO)3Cl] complexes (M = Ru, Os, en = ethylenediamine) in the presence of triethanolamine (TEOA), R3N (R = -CH2CH2OH), in DCM and DMF solvents, were studied by means of DFT/TDDFT electronic structure calculations. The geometric and free energy reaction profiles for two possible reaction pathways were calculated. Both reaction pathways studied, start with the 17e-, catalytically active intermediate, [(en)M(CO)3]˙+ generated from the first triplet excited state, T1 upon reductive quenching by TEOA which acts as a sacrificial electron donor. In the first possible pathway, TEOA- anion binds to the metal center of the catalytically active intermediate, [(en)M(CO)3]˙+ followed by CO2 insertion into the M-OCH2CH2NR2 bond. The latter upon successive protonations releases a metal 'free' [R2NCH2CH2OC(O)(OH)] intermediate which starts a new and final catalytic cycle, leading to the formation of CO and H2O while regenarating TEOA. In the second possible pathway, the 17e-, catalytically active intermediate, [(en)M(CO)3]˙+ captures CO2 molecule, forming an η1-CO2 complex. Upon 2H+/2e- successive protonations and reductions, CO product is obtained along with regenarating the catalytically active intermediate [(en)M(CO)3]˙+. The nature of the proton donor affects the reaction profiles of both mechanisms. The nature of the solvent does not affect significantly the reaction mechanisms under study. Finally, since photoexcitation and T1 reductive quenching are common to both pathways, we have srutinized the photophysical properties of the [(en)M(CO)3Cl] complexes along with their T1 excited states reduction potentials, . The [(en)M(CO)3Cl] complexes absorb mainly in the UV region while the absolute are in the range 6.4-0.9 eV.

Experimental and Theoretical Investigation of the Mechanism of the Reduction of O2 from Air to O22- by VIVO2+-N,N,N-Amidate Compounds and Their Potential Use in Fuel Cells.

The two-electron reductive activation of O2 to O22- is of particular interest to the scientific community mainly due to the use of peroxides as green oxidants and in powerful fuel cells. Despite of the great importance of vanadium(IV) species to activate the two-electron reductive activation of O2, the mechanism is still unclear. Reaction of VIVO2+ species with the tridentate-planar N,N,N-carboxamide (ΗL) ligands in solution (CH3OH:H2O) under atmospheric O2, at room temperature, resulted in the quick formation of [VV(═O)(η2-O2)(κ3-L)(H2O)] and cis-[VV(═O)2(κ3-L)] compounds. Oxidation of the VIVO2+ complexes with the sterically hindered tridentate-planar N,N,N-carboxamide ligands by atmospheric O2 gave only cis-[VV(═O)2(κ3-L)] compounds. The mechanism of formation of [VV(═O)(η2-O2)(κ3-L)(H2O)] (I) and cis-[VV(═O)2(κ3-L)] (II) complexes vs time, from the interaction of [VIV(═O)(κ3-L)(Η2Ο)2]+ with atmospheric O2, was investigated with 51V, 1H NMR, UV-vis, cw-X-band EPR, and 18O2 labeling IR and resonance Raman spectroscopies revealing the formation of a stable intermediate (Id). EPR, MS, and theoretical calculations of the mechanism of the formation of I and II revealed a pathway, through a binuclear [VIV(═O)(κ3-L)(H2O)(η1,η1-O2)VIV(═O)(κ3-L)(H2O)]2+ intermediate. The results from cw-EPR, 1H NMR spectroscopies, cyclic voltammetry, and the reactivity of the complexes [VIV(═O)(κ3-L)(Η2Ο)2]+ toward O2 reduction fit better to an intermediate with a binuclear nature. Dynamic experiments in combination with computational calculations were undertaken to fully elucidate the mechanism of the O2 reduction to O22- by [VIV(═O)(κ3-L)(Η2Ο)2]+. The galvanic cell {Zn|VIII,VII||Id, [VIVO(κ3-L)(H2O)2]+|O2|C(s)} was manufactured, demonstrating the important applicability of this new chemistry to Zn|H2O2 fuel cells technology generating H2O2 in situ from the atmospheric O2.

Hafnium(IV) Chemistry with Imide-Dioxime and Catecholate-Oxime Ligands: Unique {Hf5} and Metalloaromatic {Hf6}-Oxo Clusters Exhibiting Fluorescence.

Hafnium(IV) molecular species have gained increasing attention due to their numerous applications ranging from high-resolution nanolithography, heterogeneous catalysis, and electronics to the design of molecule-based building blocks in metal-organic frameworks (MOFs), with applications in gas separation, sorption, luminescence sensing, and interim storage of radioactive waste. Despite great potential, their chemistry is relatively underdeveloped. Here, we use strong chelators (2Z-6Z)-piperidine-2,6-dione (H3pidiox) and 2,3-dihydroxybenzaldehyde oxime (H3dihybo) to synthesize the first ever reported pentanuclear {Hf5/H3pidiox} and hexanuclear {Hf6/H3dihybo} clusters (HfOCs). The {Hf6} clusters adopt unique core structures [Hf6IV(µ3-O)2(µ-O)3] with a trigonal-prismatic arrangement of the six hafnium atoms and have been characterized via single-crystal X-ray diffraction analysis, UV-vis spectroscopy in the solid state, NMR, fluorescence spectroscopy, and high-resolution mass spectrometry in solution. One-dimensional (1D) and two-dimensional (2D) 1H NMR and mass spectroscopies reveal the exceptional thermodynamic stability of the HfOCs in solution. Interestingly, the conjunction of the oxime group with the catechol resulted in the remarkable reduction of the clusters' band gap, below 2.51 eV. Another prominent feature is the occurrence of pronounced metalloaromaticity of the triangular {Hf3} metallic component revealed by its NICSzz scan curve calculated by means of density functional theory (DFT). The NICSzz(1) value of -44.6 ppm is considerably higher than the -29.7 ppm found at the same level of theory for the benzene ring. Finally, we investigated the luminescence properties of the clusters where 1 emits light in the violet region despite the lack of fluorescence of the free H3pidiox ligand, whereas the {Hf6} 3 shifts the violet-emitting light of the H3dihybo to lower energy. DFT calculations show that this fluorescence behavior stems from ligand-centered molecular orbital transitions and that HfIV coordination has a modulating effect on the photophysics of these HfOCs. This work not only represents a significant milestone in the construction of stable low-band-gap multinuclear HfIV clusters with unique structural features and metal-centered aromaticity but also reveals the potential of Hf(IV) molecule-based materials with applications in sensing, catalysis, and electronic devices.

A Combined Experimental and Theoretical Investigation of Oxidation Catalysis by cis-[VIV(O)(Cl/F)(N4)]+ Species Mimicking the Active Center of Metal-Enzymes.

Reaction of VIVOCl2 with the nonplanar tetradentate N4 bis-quinoline ligands yielded four oxidovanadium(IV) compounds of the general formula cis-[VIV(O)(Cl)(N4)]Cl. Sequential treatment of the two nonmethylated N4 oxidovanadium(IV) compounds with KF and NaClO4 resulted in the isolation of the species with the general formula cis-[VIV(O)(F)(N4)]ClO4. In marked contrast, the methylated N4 oxidovanadium(IV) derivatives are inert toward KF reaction due to steric hindrance, as evidenced by EPR and theoretical calculations. The oxidovanadium(IV) compounds were characterized by single-crystal X-ray structure analysis, cw EPR spectroscopy, and magnetic susceptibility. The crystallographic characterization showed that the vanadium compounds have a highly distorted octahedral coordination environment and the d(VIV-F) = 1.834(1) Å is the shortest to be reported for (oxido)(fluorido)vanadium(IV) compounds. The experimental EPR parameters of the VIVO2+ species deviate from the ones calculated by the empirical additivity relationship and can be attributed to the axial donor atom trans to the oxido group and the distorted VIV coordination environment. The vanadium compounds act as catalysts toward alkane oxidation by aqueous H2O2 with moderate ΤΟΝ up to 293 and product yields of up to 29% (based on alkane); the vanadium(IV) is oxidized to vanadium(V), and the ligands remain bound to the vanadium atom during the catalysis, as determined by 51V and 1H NMR spectroscopies. The cw X-band EPR studies proved that the mechanism of the catalytic reaction is through hydroxyl radicals. The chloride substitution reaction in the cis-[VIV(O)(Cl)(N4)]+ species by fluoride and the mechanism of the alkane oxidation were studied by DFT calculations.

DFT insights into the photocatalytic reduction of CO2 to CO by Re(I) complexes: the crucial role of the triethanolamine "magic" sacrificial electron donor.

The reaction mechanism for the photocatalytic reduction of CO2 to CO catalyzed by the [Re(en)(CO)3Cl] complex in the presence of triethanolamine, R3N (R = CH2CH2OH) abbreviated as TEOA, in DMF solution was studied in-depth with the aid of DFT computational protocols by calculating the geometric and free energy reaction profiles for several possible reaction pathways. The reaction pathways studied start with the "real" catalytic species [Re(en)(CO)3], [Re(en)(CO)3]- and/or [Re(en)(CO)2Cl]- generated from the excited triplet T1 state upon single and double reductive quenching by a TEOA sacrificial electron donor or photodissociation of a CO ligand. The first step in all the catalytic cycles investigated involves the capture of either CO2 or the oxidized R2NCH2CH2O˙ radical. In the latter case, the CO2 molecule is captured (inserted) by the Re-OCH2CH2NR2 bond forming stable intermediates. Next, successive protonations (TEOA also acts as a proton donor) lead to the release of CO either from the energy consuming 2e- reduction of [Re(en)(CO)4]+ or [Re(en)(CO)2Cl]+ complexes in the CO2 capture pathways or from the released unstable diprotonated [R2NCH2CH2OC(OH)(OH)]+ species regenerating TEOA and the catalyst. The CO2 insertion reaction pathway is the favorable pathway for the photocatalytic reduction of CO2 → CO catalyzed by the [Re(en)(CO)3Cl] complex in the presence of TEOA manifesting its crucial role as an electron and proton donor, capturing CO2 and releasing CO.

Anomeric and Perlin Effect Ladders for 2-Substituted 2-Fluorotetrahydro-2H-pyrans Using Sensitive Structural, Energetic, and NMR Probes.

A comprehensive exploration of the anomeric and Perlin effects in a series of 2-substituted-2-fluorotetrahydro-2H-pyrans employing sensitive structural, energetic, and NMR probes calculated by density functional theory (DFT) and natural bond orbital (NBO) approaches is undertaken. We used a wide variety of X substituents exhibiting diverse electronic features (σ-donors, σ-donors/π-donors, and σ-donors/π-acceptors). It is noteworthy that a group of 8 substituents (NHMe, SCN, OBr, NO3, OCl, Cl, OF, and Br) favor the axial conformations, while a group of 13 substituents (NO2, NF2, NH2, CN, SH, H, N3, B(OH)2, OMe, BH2, OH, Me, and Ph) favor the equatorial conformations. Interestingly, a group of 6 substituents (NH2, NHMe, NF2, OF, OCl, and OBr) are responsible for the observed normal Perlin effect while the remaining 16 substituents induce the reverse Perlin effect. An exhaustive investigation of possible correlations of anomeric and Perlin effect descriptors with structural, energetic, one-bond 1JC-F couplings and the nucleophilicity of X descriptors demonstrated the general relationship of the Perlin and anomeric effects and manifested their common stereoelectronic origin.

Synthesis, Structural, and Physicochemical Characterization of a Ti6 and a Unique Type of Zr6 Oxo Clusters Bearing an Electron-Rich Unsymmetrical {OON} Catecholate/Oxime Ligand and Exhibiting Metalloaromaticity.

The chelating catechol/oxime ligand 2,3-dihydroxybenzaldehyde oxime (H3dihybo) has been used to synthesize one titanium(IV) and two zirconium(IV) compounds that have been characterized by single-crystal X-ray diffraction and 1H and 13C NMR, solid-state UV-vis, and ESI-MS spectroscopy. The reaction of TiCl4 with H3dihybo and KOH in methanol, at ambient temperature, yielded the hexanuclear titanium(IV) compound K2[TiIV6(µ3-O)2(µ-O)3(OCH3)4(CH3OH)2(µ-Hdihybo)6]·CH3OH (1), while the reaction of ZrCl4 with H3dihybo and either nBu4NOH or KOH also gave the hexanuclear zirconium(IV) compounds 2 and 3, respectively. Compounds 1-3 have the same structural motif [MIV6(µ3-Ο)2(µ-Ο)3] (M = Ti, Zr), which constitutes a unique example with a trigonal-prismatic arrangement of the six zirconium atoms, in marked contrast to the octahedral arrangement of the six zirconium atoms in all the Zr6 clusters reported thus far, and a unique Zr6 core structure. Multinuclear NMR solution measurements in methanol and water proved that the hexanuclear clusters 1 and 3 retain their integrity. The marriage of the catechol moiety with the oxime group in the ligand H3dihybo proved to be quite efficient in substantially reducing the band gaps of TiO2 and ZrO2 to 1.48 and 2.34 eV for the titanium and zirconium compounds 1 and 3, respectively. The application of 1 and 3 in photocurrent responses was investigated. ESI-MS measurements of the clusters 1 and 3 revealed the existence of the hexanuclear metal core and also the initial formation of trinuclear M3 (M = Ti, Zr) building blocks prior to their self-assembly into the hexanuclear M6 (M = Ti, Zr) species. Density functional theory (DFT) calculations of the NICSzz scan curves of these systems revealed that the triangular M3 (M = Ti, Zr) metallic ring cores exhibit pronounced metalloaromaticity. The latter depends upon the nature of the metallic center with NICSzz(1) values equal to -30 and -42 ppm for the Ti (compound 1) and Zr (compound 2) systems, respectively, comparable to the NICSzz(1) value of the benzene ring of -29.7 ppm calculated at the same level of theory.

cis- and trans-Ligand Effects on the Inverse trans-Influence in [UVI(O)(L)Cl4]0/- (L = Unidentate Ligand) Complexes.

A comprehensive exploration of the inverse trans-influence (ITI) phenomenon in a series of cis-[UVI(O)(L)Cl4]0/- and trans-[UVI(O)(L)Cl4]0/- complexes involving a wide variety of neutral and anionic unidentate ligands L, using relativistic density functional theory, threw light on the still-intriguing physics of ITI, elucidated its origin, and deployed the ligands L in cis- and trans-ITI sequences (ladders). ITI is produced for the complete set of L in both series of [U(O)(L)Cl4]0/- complexes, but this is not reflected in the thermodynamic stability of the [U(O)(L)Cl4]0/- isomers. In effect the hard and strong σ-donor anionic ligands stabilize the trans isomers, but the opposite is true for the soft σ-donor/π-donor neutral and anionic ligands that stabilize the cis isomers. According to the ITI%(U-L) metrics the hard strong σ-donor anionic ligands exert stronger ITI than the soft σ-donor/π-donor neutral ones, while according to the ITI%(U-O) metrics ITI is produced only for the more stable trans-[U(O)(L)Cl4]0/- isomers involving the anionic ligands. In contrast the neutral ligands in the more stable cis-[U(O)(L)Cl4]0/- isomers produce the normal cis influence (CI). Furthermore, the more electronegative ligands produce stronger ITI. ITI%(U-O) cis- and trans-philicity ladders are also built for both series of complexes employing the isotropic σiso(SO) 17O NMR shielding constants as a sensitive metric of the ITI phenomenon. The NMR ITI%(U-O) metrics are consistent with the ITI%(U-O) ones illustrating that the isotropic 17O NMR shifts are sensitive metrics of the covalency of the multiple U-O bonding mode and, hence, of the ITI phenomenon. Interestingly the 2σ BD(U-O) natural bond orbitals play a key role in tuning the bond length and covalency of the U-O bond through the 2σ(U≡O) → 2σ*(U≡O) hyperconjugative interactions. The assessment of the magnitude of the ITI in the [UVI(O)(L)Cl4]0/- complexes and the recognition of the factors affecting ITI dispose a guide to experimentalists working in the area of uranium chemistry to develop strategies for stabilizing uranium-ligand linkages.

Correction: DFT/TDDFT insights into the chemistry, biochemistry and photophysics of copper coordination compounds.

[This corrects the article DOI: 10.1039/C4RA04921G.].

Trans-philicity (trans-influence/trans-effect) ladders for square planar platinum(II) complexes constructed by 35 Cl NMR probe.

The unified term of trans-philicity is proposed to cover the trans-effect/trans-influence concepts. NMR trans-philicity ladders are built for a broad series of square planar trans-Pt(NH3 )2 (Cl)L and trans-Pt(CO)2 (Cl)L complexes employing 35 Cl NMR probe and quantified by calculation of NMR trans-philicity indicators. The trans-philicity is linearly correlated with the ligand electronic PL constant, a measure of the net donor power of the ligand. The nature of cis-ligands does not affect trans-philicity ladders but strongly affects trans-philicity strength. Solvent has significant effect on the σcalcd 35 Cl shielding constants, with the polar Dimethylformamide (DMF) solvent inducing downfield shifts relative to σcalcd 35 Cl with nonpolar benzene solvent. Good correlations between σcalcd 35 Cl shielding constants and the estimated R(Pt-Cl) bond distances demonstrate the relation of trans-philicity with trans-influence and trans-effect phenomena and put the grounds for the establishment of the new concept of trans-philicity in the realm of square planar Pt(II) and other transition metal complexes. © 2019 Wiley Periodicals, Inc.

Dinuclear and Mononuclear Rhenium Coordination Compounds upon Employment of a Schiff-Base Triol Ligand: Structural, Magnetic, and Computational Studies.

The 1:1 reaction of trans-[ReIIICl3(PPh3)2(MeCN)] with 2-(ß-naphthalideneamino)-2-hydroxymethyl-1-propanol, H3L, in toluene gave the dinuclear complex [ReIII2Cl4(HL)(PPh3)]·2C7H8 (1·2C7H8), while the 1:2 reaction led to the formation of complex [ReIVCl2(HL)(PPh3)] (2). In both species, the Schiff-base ligand exists in its doubly deprotonated form, HL2-, forming chelate rings around the metallic centers. In addition, 1·2C7H8 displays a unique triple metal-to-metal bond between the two trivalent rhenium ions separated at a 2.229(1) Å bond distance, while in complex [ReIVCl2(HL)(PPh3)] (2) the two aromatic ligands, HL2- and PPh3, occupy axial positions, with the terminal Cl- ions in the trans position. Investigation of the magnetic properties revealed a Curie paramagnetic behavior ( S = 1/2) with a pronounced temperature independent paramagnetism (TIP) for 1·2C7H8 and 2. Both the geometry and the electronic structure of both compounds have been studied by means of density functional theory (DFT) calculations, confirming the triplet and doublet spin ground state of the complexes and furthermore establishing an electron-rich σ2π4δ1δ*1 bond order of 3 for 1·2C7H8. In addition, the absorption spectrum of 1·2C7H8 in CH2Cl2 was simulated by means of DFT calculations and is in excellent agreement with both the crystallographic and theoretical studies. Complex 1·2C7H8 is the first dinuclear rhenium complex with a triple metal-metal bond between trivalent rhenium centers.

Synthesis, structural and physicochemical characterization of a new type Ti6-oxo cluster protected by a cyclic imide dioxime ligand.

Reaction of the cyclic ligand (2Z,6Z)-piperidine-2,6-dione dioxime with TiCl4 and KOH yielded the hexanuclear cluster K6[TiIV6(µ3-O)2(µ2-O)3(CH3O)6(µ2-η1,η1,η2-Hpidiox-O,N,O')4(µ2-η1,η1,η2-pidiox-O,N,O')2]·7.5CH3OH possessing a new {Ti6O5} structural motif. The cluster core {Ti6O5} is wrapped by external tripodal imide dioxime ligands, showing good solubility and stability and thus, allowing its solution to be studied by means of electrospray ionization mass spectrometry, electrochemistry and 2D NMR, c. w. EPR and UV-vis spectroscopies. Density Functional Theory (DFT) calculations reveal that the cyclo-Ti3 metallic cores exhibit metallaromaticity which is expected to contribute to the stabilization of this system.

Investigation of dioxygen activation by copper(ii)-iminate/aminate complexes.

The activation of dioxygen by metal ions is critical in chemical and bio-chemical processes. A scientific challenge is the elucidation of the activation site of dioxygen in some copper metalloproteins, which is either the metal center or the substrate. In an effort to address this challenge, we prepared a series of new copper(ii) complexes (1·2H2O, 2·CH3OH, 3) with bio-inspired amidate ligands and investigated their activity towards dioxygen activation. The secondary amine group ligated to copper(ii) of the complex 1·2H2O in methyl alcohol is oxidized (2e-) by air dioxygen in a stepwise fashion to an imine group, affording complex 2. The copper(ii) complex 2 in methyl alcohol induces the 4e- oxidation by air dioxygen of the imine functionality ligated to copper(ii) to an azinate group, resulting in the isolation of a dinuclear azinate copper(ii) compound (4). Experimental and computational studies, including X-band c. w. EPR, UV-vis and ESI-MS spectroscopy and density functional theory computations, indicate a direct attack of the dioxygen on the -HC[double bond, length as m-dash]N- group ligated to copper(ii), and a possible mechanism of the oxidation of the -HC[double bond, length as m-dash]N- functionality ligated to copper(ii) to an azinate group is provided. This unprecedented activation of dioxygen by a copper substrate paves the way for further exploration of the O2 activation mechanisms in enzymes and the development of effective catalysts in O2-involved green organic synthesis.

Design and Assembly of Covalently Functionalised Polyoxofluorovanadate Molecular Hybrids.

Mixed-valent polyoxometalate (POM) clusters are one of the most interesting host species, showing a wide range of structural features and properties. The facile preparation and functionalisation of a mixed-valent polyoxofluorovanadates is reported, where two electrons are trapped to antipodal sites of the clusters. The first members of this family of clusters with the general formula, [VV12 VIV2 O16 (µ-O)10 (µ3 -O)10 (µ3 -F)2 (L)2 ]6- , where L: py=pyridine (1); pyr=pyrazine (2); im=imidazole (3), are unique organic-inorganic hybrids with the addition of a N-donor ligand at either end of the polyoxofluorovanadate. The composition and connectivity of 1-3 were characterised by single-crystal X-ray diffraction and electrospray ionisation mass spectrometry. Electron paramagnetic resonance spectroscopy revealed that the two well-separated VIV ions in each cluster are fully uncoupled with J=0, giving a degenerate singlet-triplet ground state. This attenuation of the exchange interaction is probed with density functional theoretical calculations that reveal that the inclusion of the fluoride ion in the cluster produces a bond pathway biased toward destructive interference between competing ferromagnetic and antiferromagnetic interactions. These robust molecular materials are the ideal combination of desirable electronic properties, with an organic handle with which they can be integrated into spintronic circuitry for molecular devices.

3d/4f Coordination Clusters as Cooperative Catalysts for Highly Diastereoselective Michael Addition Reactions.

Michael addition (MA) is one of the most well studied chemical transformation in synthetic chemistry. Here, we report the synthesis and crystal structures of a library of 3d/4f coordination clusters (CCs) formulated as [ZnII2YIII2L4(solv)X(Z)Y] and study their catalytic properties toward the MA of nitrostyrenes with barbituric acid derivatives. Each CC presents two borderline hard/soft Lewis acidic ZnII centers and two hard Lewis acidic YIII centers in a defect dicubane topology that brings the two different metals into a proximity of ∼3.3 Å. Density functional theory computational studies suggest that these tetrametallic CCs dissociate in solution to give two catalytically active dimers, each containing one 3d and one 4f metal that act cooperatively. The mechanism of catalysis has been corroborated via NMR, electron paramagnetic resonance, and UV-vis. The present work demonstrates for the first time the successful use of 3d/4f CCs as efficient and high diastereoselective catalysts in MA reactions.

Exploring possible reaction pathways for the o-atom transfer reactions to unsaturated substrates catalyzed by a [Ni-NO2 ] ↔ [Ni-NO] redox couple using DFT methods.

The (nitro)(N-methyldithiocarbamato)(trimethylphospane)nickel(II), [Ni(NO2 )(S2 CNHMe)(PMe3 )] complex catalyses efficiently the O-atom transfer reactions to CO and acetylene. Energetically feasible sequence of elementary steps involved in the catalytic cycle of the air oxidation of CO and acetylene are proposed promoted by the Ni(NO2 )(S2 CNHMe)(PMe3 )] ↔ Ni(NO2 )(S2 CNHMe)(PMe3 ) redox couple using DFT methods both in vacuum and dichloromethane solutions. The catalytic air oxidation of HC≡CH involves formation of a five-member metallacycle intermediate, via a [3 + 2] cyclo-addition reaction of HC≡CH to the Ni-N = O moiety of the Ni(NO2 )(S2 CNHMe)(PMe3 )] complex, followed by a ß H-atom migration toward the Cα carbon atom of the coordinated acetylene and release of the oxidation product (ketene). The geometric and energetic reaction profile for the reversible [Ni( κN1-NO2 )(S2 CNHMe)(PMe3 )] ⇌ [Ni( κO,O2-ONO)(S2 CNHMe)(PMe3 )] linkage isomerization has also been modeled by DFT calculations. © 2017 Wiley Periodicals, Inc.

Highly Efficient Sorption of Methyl Orange by a Metal-Organic Resin-Alginic Acid Composite.

The composite anion-exchange material MOR-1-HA (metal-organic resin-1-alginic acid) was investigated as sorbent for the capture of the methyl orange anion (MO- ) from aqueous solutions. MOR-1-HA shows a remarkably high sorption capacity (up to 859 mg g-1 ) and rapid sorption kinetics, the fastest among the reported metal-organic sorbents. It is capable of absorbing MO- over a wide pH range (1-8) and, in addition, it exhibits significant MO- sorption affinity even in the presence of large excesses of competing anions (e.g., Cl- , NO3 - , SO4 2- ). The exceptional MO- -sorption properties of MOR-1-HA arise not only from its highly porous structure and easily exchangeable Cl- anions, but also from a multitude of interaction effects, such as electrostatic interactions between MO- and the NH3 + groups of the material, hydration/dehydration, hydrophobicity/hydrophilicity, size and capacity of generating lateral interactions, and intercalation as revealed by theoretical studies. An ion-exchange column with a stationary phase containing MOR-1-HA and silica sand showed high efficiency for the removal of MO- from various types of aqueous samples. The column can be readily regenerated and reused for many runs with minimal loss (2.3-9.3 %) of its exchange capacity. The simplicity of the MOR-1-HA/sand column and its high regeneration capability and reusability make it particularly attractive for application in the remediation of MO- -contaminated industrial wastewater.

195 Pt NMR parameters as strong descriptors in one-parameter QSAR models for platinum-based antitumor compounds.

Highly predictive one-parameter quantitative structure-activity relationship models have been developed for platinum-based anticancer drugs using the 195 Pt NMR parameters as strong descriptors. The developed quantitative structure-activity relationship models were applied in diverse homogeneous sets of antiproliferative Pt(II) and Pt(IV) compounds. These observations form the basis for making predictions of cytotoxicity for a broad range of platinum-based antitumor compounds just from inspection of calculated or experimentally determined 195 Pt NMR parameters. Copyright © 2016 John Wiley & Sons, Ltd.

Prediction of 195 Pt NMR of photoactivable diazido- and azine-Pt(IV) anticancer agents by DFT computational protocols.

195 Pt NMR chemical shifts for a series of large-sized photoactivable anticancer diazido-Pt(IV), homopiperizine-Pt(IV) and multifunctional azine-Pt(IV) complexes hardly to be probed experimentally and by sophisticated four-component and two-component relativistic calculations are predicted with high accuracy by density functional theory computational protocols. The calculated 195 Pt NMR chemical shifts constitute a crucial descriptor for making highly predictive one-parameter quantitative structure activity relationships models that help in designing photoactivable Pt(IV)-based antitumor agents with high cytotoxicity and selectivity. Copyright © 2016 John Wiley & Sons, Ltd.

Prediction of (195) Pt NMR chemical shifts of dissolution products of H2 [Pt(OH)6 ] in nitric acid solutions by DFT methods: how important are the counter-ion effects?

(195) Pt NMR chemical shifts of octahedral Pt(IV) complexes with general formula [Pt(NO3 )n (OH)6 - n ](2-) , [Pt(NO3 )n (OH2 )6 - n ](4 - n) (n = 1-6), and [Pt(NO3 )6 - n - m (OH)m (OH2 )n ](-2 + n - m) formed by dissolution of platinic acid, H2 [Pt(OH)6 ], in aqueous nitric acid solutions are calculated employing density functional theory methods. Particularly, the gauge-including atomic orbitals (GIAO)-PBE0/segmented all-electron relativistically contracted-zeroth-order regular approximation (SARC-ZORA)(Pt) ∪ 6-31G(d,p)(E)/Polarizable Continuum Model computational protocol performs the best. Excellent second-order polynomial plots of δcalcd ((195) Pt) versus δexptl ((195) Pt) chemical shifts and δcalcd ((195) Pt) versus the natural atomic charge QPt are obtained. Despite of neglecting relativistic and spin orbit effects the good agreement of the calculated δ (195) Pt chemical shifts with experimental values is probably because of the fact that the contribution of relativistic and spin orbit effects to computed σ(iso) (195) Pt magnetic shielding of Pt(IV) coordination compounds is effectively cancelled in the computed δ (195) Pt chemical shifts, because the relativistic corrections are expected to be similar in the complexes and the proper reference standard used. To probe the counter-ion effects on the (195) Pt NMR chemical shifts of the anionic [Pt(NO3 )n (OH)6 - n ](2-) and cationic [Pt(NO3 )n (OH2 )6 - n ](4 - n) (n = 0-3) complexes we calculated the (195) Pt NMR chemical shifts of the neutral (PyH)2 [Pt(NO3 )n (OH)6 - n ] (n = 1-6; PyH = pyridinium cation, C5 H5 NH(+) ) and [Pt(NO3 )n (H2 O)6 - n ](NO3 )4 - n (n = 0-3) complexes. Counter-anion effects are very important for the accurate prediction of the (195) Pt NMR chemical shifts of the cationic [Pt(NO3 )n (OH2 )6 - n ](4 - n) complexes, while counter-cation effects are less important for the anionic [Pt(NO3 )n (OH)6 - n ](2-) complexes. The simple computational protocol is easily implemented even by synthetic chemists in platinum coordination chemistry that dispose limited software availability, or locally existing routines and knowhow. Copyright © 2016 John Wiley & Sons, Ltd.