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The peculiarities of the optical properties of 2-aryl-1,2,3-triazole acids and their sodium salts were investigated in different solvents (1,4-dioxane, dimethyl sulfoxide DMSO, methanol MeOH) and in mixtures with water. The results were discussed in terms of the molecular structure formed by inter- and intramolecular noncovalent interactions (NCIs) and their ability to ionize in anions. Theoretical calculations using the Time-Dependent Density Functional Theory (TDDFT) were carried out in different solvents to support the results. In polar and nonpolar solvents (DMSO, 1,4-dioxane), fluorescence was provided by strong neutral associates. Protic MeOH can weaken the acid molecules’ association, forming other fluorescent species. The fluorescent species in water exhibited similar optical characteristics to those of triazole salts; therefore, their anionic character can be assumed. Experimental 1H and 13C-NMR spectra were compared to their corresponding calculated spectra using the Gauge-Independent Atomic Orbital (GIAO) method and several relationships were established. All these findings showed that the obtained photophysical properties of the 2-aryl-1,2,3-triazole acids noticeably depend on the environment and, therefore, are good candidates as sensors for the identification of analytes with labile protons.

S-formylglutathione hydrolases (SFGHs) catalyze the hydrolysis of S-formylglutathione to formate and glutathione using the conserved serine hydrolase catalytic triad residues (Ser-His-Asp). SFGHs have broad substrate specificity, including, for example, ester bond-containing substrates. Here, we report the crystal structure of Burkholderiaceae sp. SFGH (BuSFGH) at 1.73 Å resolution. Structural analysis showed that the overall structure of BuSFGH has a typical α/β hydrolase fold, with a central β-sheet surrounded by α-helices. Analytical ultracentrifugation analysis showed that BuSFGH formed a stable dimer in solution. The enzyme activity assay indicated that BuSFGH has a high preference for short-chain p-nitrophenyl esters, such as p-nitrophenyl acetate. The activity of BuSFGH toward p-nitrophenyl acetate was five times higher than that of p-nitrophenyl butylate. Molecular modeling studies on the p-nitrophenyl acetate-bound BuSFGH structure indicate that Gly52, Leu53, Trp96, His147, Ser148, Trp182, Phe228, and His259 residues may be crucial for substrate binding. Collectively, these results are useful for understanding the substrate-binding mechanism and substrate specificity of BuSFGH. They can also provide useful insights for designing modified BuSFGHs with different substrate specificities.

In recent years, a number of achiral liquid crystal dimer molecules have been shown to exhibit nematic–nematic phase transitions. The lower temperature phase has been identified as the NTB phase, which demonstrates emergent chirality in the spontaneous formation of a heliconical structure. Recent fully atomistic simulations of the molecule CB7CB (1,7-bis-4-(4′-cyanobiphenyl) heptane), a dimer with an odd number of carbon spacers between the mesogenic parts of the molecule, have captured the NTB–N–I phase sequence, providing a picture of the order at a molecular level. In this paper, we use atomistic simulations of CB7CB to develop a coarse-grained model using systematic coarse graining in the NTB phase. We use both force matching (in the form of the MS-CG method) and iterative Boltzmann inversion (IBI) methodologies. Both techniques capture the heliconical order within the NTB phase. Moreover, the model developed via force matching is shown to provide an excellent representation of the atomistic simulation reference model and, remarkably, demonstrates good transferability across temperatures, allowing the NTB–N and N–I phase transitions to be simulated. We also compare results with those of a Martini 3-based coarse-grained model.

A comprehensive study of saturated vapors of 4-n-propyloxybenzoic acid (POBA) by gas electron diffraction (GED) and mass spectrometric (MS) methods supplemented by quantum chemical (QC) calculations was carried out for the first time. An attempt was made to detect dimeric forms of the acid in the gaseous state. It has been established that at the temperature of GED experiment, vapor over a solid sample contains up to 20 mol.% of cyclic dimers with two O-H...O hydrogen bonds. The main geometrical parameters of gaseous monomers and dimers of POBA are obtained. The distance r(O…O) = 2.574(12) Å in the cyclic fragment of the gaseous dimer is close to that in the crystal structure (2.611 Å). In the mass spectrum of the POBA recorded the ions of low intensity with a mass exceeding the molecular mass of the monomer were detected. The presence of ions, whose elemental composition corresponds to the dissociative ionization of the dimer, confirms the results of the GED experiment on the presence of POBA dimers in the gas state. The results of GED studies of acetic acid, benzoic acid, and POBA were compared. It is shown that the COOH fragment saves its geometric structure in monomers, as well as the COOH...HOOC fragment with two hydrogen bonds in dimers of different acids. The intermolecular interaction energy in considered acid dimers was estimated using QC calculations (B97D/6-311++G **). The significant value of last (>84 kJ/mol) is the reason for the noticeable presence of dimers in the gas phase.

Metal string complexes, linearly aligned transition metal arrays coordinated with the multidentate organic ligands, have gained much attention both in unique electronic/structural properties and in potential applications as conductive molecular nanowires. Here we report on a dimerized NiII trinuclear complex, [Ni6Cl2(dpa)8](I5)2·0.25I2 (dpa- = 2,2'-dipyridylamide anion). X-ray structural analysis revealed that two trinuclear moieties are bridged by a Cl anion to form a dimerized string structure. This is the first example of two Ni string complexes that are connected. In the electronic absorption and Raman spectra, characteristic absorption bands and a vibration mode based on the dimer string structure were observed. In the solid state, dimer complexes align in one dimension in an MMMXMMMX (M = metal, X = halogen) manner, leading to the intra- and interdimer antiferromagnetic interactions.

The Lewis acid-base adducts MoF5(NC5H5)n and MoOF4(NC5H5)n (n = 1, 2) were synthesized from the reactions of MoF5 and MoOF4 with C5H5N and structurally characterized by X-ray crystallography. Whereas the crystal structures of MoF5(NC5H5)2 and MoOF4(NC5H5)2 are isomorphous containing pentagonal-bipyramidal molecules, the fluorido-bridged, heptacoordinate [MoF5(NC5H5)]2 dimer differs starkly from monomeric, hexacoordinate MoOF4(NC5H5). For the weaker Lewis base CH3CN, only the 1:1 adduct, MoF5(NCCH3), could be isolated. All adducts were characterized by Raman spectroscopy in conjunction with vibrational frequency calculations. Multinuclear NMR spectroscopy revealed an unprecedented isomerism of MoOF4(NC5H5)2 in solution, with the pyridyl ligands occupying adjacent or nonadjacent positions in the equatorial plane of the pentagonal bipyramid. Paramagnetic MoF5(NC5H5)2 was characterized by electron paramagnetic resonance (EPR) spectroscopy as a dispersion in solid adamantane as well as in a diamagnetic host lattice of MoOF4(NC5H5)2; EPR parameters were computed using ZORA with the BPW91 functional using relativistic all-electron wave functions for Mo and simulated using EasySpin. Density functional theory calculations (B3LYP) and natural bond orbital analyses were conducted to elucidate the distinctive bonding and structural properties of all adducts reported herein and explore fundamental differences observed in the Lewis acid behavior of MoF5 and MoOF4.

Two Ni(II) carboxyphosphonates, namely [Ni(H4L)2] (1) and [Ni(H3L)(H2O)]·2H2O (2) (H5L=HOOCC6H4CH2N(CH2PO3H2)2), have been hydrothermally synthesized. Structural analyses reveal that 1 shows a two-dimensional (2D) inorganic layer structure, and the layers are further packed into a three-dimensional (3D) supramolecular structure through the interlayer hydrogen-bonding interactions. In 2, two adjacent {NiO5N} polyhedra are connected to form a {Ni2O8N2} dimer, and these dimers are further linked by {CPO3} tetrahedra to form a one-dimensional (1D) chain. Consecutive chains are further connected by the intermolecular hydrogen-bonding interactions, resulting in a 2D supramolecular layer structure. Magnetic analyses exhibited that 1 shows major antiferromagnetic behavior, whereas 2 displays ferromagnetic interactions at low temperatures. Meanwhile, the magnetic properties of 1 and 2 have also been quantified using the Curie–Weiss law and the PHI program package, respectively. Two nickel(II) carboxyphosphonates with different structures showed different magnetic behaviors. Meanwhile, the magnetic properties of 1 and 2 have also been quantified using the Curie–Weiss law and the PHI program package.

The adducts between luminescent lanthanide tris(β-diketonate)s and diimine or triimine ligands have been explored exhaustively for their exceptional photophysical properties. Their formation, stability, and structures in solution, together with the design of extended metallopolymers exploiting these building blocks, remain, however, elusive. The systematic peripheral substitution of tridentate 2,6-bis(benzimidazol-2-yl)pyridine binding units (Lk = L1-L5), taken as building blocks for linear oligomers and polymers, allows a fine-tuning of their affinity toward neutral [Ln(hfa)3] (hfa = hexafluoroacetylacetonate) lanthanide containers in the [LkLn(hfa)3] adducts. Two trends emerge with (i) an unusual pronounced thermodynamic selectivity for midrange lanthanides (Ln = Eu) and (ii) an intriguing influence of remote peripheral substitutions of the benzimidazole rings on the affinity of the tridentate unit for [Ln(hfa)3]. These trends are amplified upon the connection of several tridentate binding units via their benzimidazole rings to give linear segmental dimers (L6) and trimers (L7), which are considered as models for programming linear Wolf-Type II metallopollymers. Modulation of the affinity between the terminal and central binding units in the linear multitridentate ligands deciphers the global decrease of metal-ligand binding strengths with an increase in the length of the receptors (monomer → dimer → trimer → polymer). Application of the site binding model shed light onto the origin of the variation of the thermodynamic affinities: a prerequisite for the programmed loading of a polymer backbone with luminescent lanthanide β-diketonates. Analysis of the crystal structures for these adducts reveals delicate correlations between the chemical bond lengths measured in the solid state (or bond valence parameters) and the metal-ligand affinities operating in solution.

The reduction of [(nacnac)MnCl]2 (1) (nacnac = HC(C(Me)N(2.6-i-Pr2C6H3))2) by potassium intercalated graphite KC8 in toluene and benzene is studied. It is established that in both cases, Mn(II) reduces to Mn(I), giving [(nacnac)Mn]2 dimer (2) with the Mn–Mn bond. In addition, solvent interaction products form. In the first case, the product of toluene meta-deprotonation [(nacnac)Mn(m-C6H4CH3)] (3) forms; in the second, the product of benzene reduction [{Mn(nacnac)}2(μ–η4:η4-C6H6)] C6H6 (4) forms. The structures of complexes 3 and 4 are determined by single crystal X-ray diffraction (XRD). A set of crystalline reaction products and their ratio is determined by quantitative powder XRD using the Rietveld method: in the case of toluene, 2, 3, and [(nacnac)MnH]2 are in a 1:1:4 ratio; in the case of benzene, 2, 4·C6H6, and 1 are in a 3:8.5:1 ratio, and also trace amounts of a crystalline phase with an unknown structure.

A variety of lithiated calix[n]arenes, for which n = 6 or 8, have been isolated, structurally characterized, and evaluated as catalysts for the ring-opening polymerization (ROP) of the cyclic esters e-caprolactone (e-CL), δ-valerolactone (δ-VL), and rac-lactide (r-LA). In particular, interaction of p-tert-butylcalix[6]areneH6 (L6H6) with LiOtBu in THF led to the isolation of [Li14(L6H)2(CO3)2(THF)6(OH2)6]·14THF (1·14THF), the core of which has a chain of five Li2O2 diamonds. Similar use of p-tert-butylcalix[8]areneH8 (L8H8) afforded [Li10(L8)(OH)2(THF)8]·7THF (2·7THF), where the core is composed of a six-rung Li-O ladder. Use of debutylated calix[8]areneH8 (deBuL8H8) led to an elongated dimer [Li18(deBuL8)2(OtBu)2(THF)14]·4THF (3·4THF) in which the calix[8]arenes possess a wavelike conformation forming bridges to link three separate LixOy clusters (where x and y = 6, ignoring the THF donor oxygens). Interaction of L8H8 with LiOH·H2O afforded [Li4(L8H4)(OH2)4(THF)6]·5.5THF (4·5.5THF), where intramolecular H-bond interactions involving Li, O, and H construct a cage in the core of the structure with six- and eight-membered rings. Lastly, addition of Me3Al to the solution generated from L8H8 and LiOtBu led to the isolation of [(AlMe2)2Li20(L8H2)2(OH2)4(O2-)4(OH)2(NCMe)12]·10MeCN (5·10MeCN) in which Li, O, Al, and N centers build a polyhedral core. These complexes have been screened for their potential to act as precatalysts in the ring-opening polymerization (ROP) of e-CL, δ-VL, and r-LA. For the ROP of e-CL, δ-VL, and r-LA, systems 1-4 exhibited moderate activity at 130 °C over 8 h. In the case of ROP using the mixed-metal (Li/Al) system 5, better conversions and high molecular weight polymers were achieved. In the case of the ROP of ω-pentadecalactone (ω-PDL), the systems proved to be inactive under the conditions employed herein.

Complexes of sodium dodecyl sulfate dimer (SDS)2 with β-alanyl-3-methyl-L-histidine dipeptide (balenine) in zwitterionic and cationic forms are simulated by the quantum chemical method DFT/B97D using the 6-311++G(3d,3p) basis set. The most stable configurations of these complexes are found. The complexes are shown to be stabilized by electrostatic forces and hydrogen bonds between the peptide and the dimer. Energy changes and hydrogen bond characteristics during complexation are analyzed. It is established that complexes with cationic balenine are more energy preferable. Balenine complexes and complexes formed by the isomeric peptide β-alanyl-1-methyl-L-histidine (anserine) are compared. As far as the formation of H-bonds with the dimer, position 1 of the balenine imidazole ring is more sterically favorable for the NH group than position 3 in the anserine ring. Structural changes in the peptide during the complexation are analyzed.

Two Ni-substituted polyoxometalates (NiSPs), [Ni6(Py)6(H2O)5(μ3-OH)3(PW9O34)]2·10H2O (1), [Ni7(Py)6(Im)(H2O)5O(WO4)(μ3-OH)3(H2PW9O34)]·3H2O (2) (Py = pyridine, Im = imidazole), were successfully hydrothermally synthesized. Compounds 1 and 2 have significantly different configurations by introducing different amounts of imidazole ligands. For compound 1, two malposed {Ni6(Py)6PW9} units that are face to face are bridged by two Ni-O-W bonds to constitute an isolated dimeric structure. Differently, the {Ni7(Py)6(Im)PW9}2 dimer in compound 2 connects with four adjacent dimers by four {WO4} groups in an interesting two-dimensional (2-D) arrangement. The magnetism of compounds 1 and 2 was studied, and magnetic test results demonstrated that both compounds have ferromagnetic interactions between the nickel centers. Meanwhile, the third-order nonlinear optical (NLO) measurements indicated that compound 1 can serve as potential nonlinear optical materials.

Initial reaction rate data for the direct esterification of 1-tetradecene with heptanoic acid on dry Amberlyst®15 catalyst permitted the identification of the surface reaction mechanism, as well as the adsorption coefficients of all reactants and products. Three different surface reaction mechanisms were considered, a two-site Langmuir–Hinshelwood mechanism and two single-site Eley–Rideal mechanisms. All the mechanisms considered competitive adsorption by all reactants and products. For each model, an error surface was calculated above the two-dimensional space of possible reactant adsorption coefficients. The error surface identified the best adsorption coefficients for each model and revealed the most likely mechanism for the surface reaction. The best mechanism was Eley–Rideal with adsorbed tetradecene reacting with heptanoic acid in the bulk phase. To explain initial rate responses to changes in initial reactant concentrations, both tetradecene and heptanoic acid must adsorb strongly to the active sites, and heptanoic acid must rapidly equilibrate between monomer and dimer forms. Data also revealed that adsorption and desorption rates were sometimes competitive with the rate of the surface reaction; equilibrium between adsorbed species and those in solution was not always maintained during short reaction times. Proper distinction between Langmuir–Hinshelwood and Eley–Rideal mechanisms required initial rate data for extreme ranges of initial reactant concentrations.

In the construction of metallosupramolecules, the reaction sequence in a three-reactant system (one ligand plus two metal ions) could be one of the controlling factors influencing the outcome of the reaction. In this work, the formation of supramolecular isomers (1 and 2) and an endo/exocyclic Cu+ complex (4) of the NS4-macrocycle (L) via different sequential metal addition protocols (routes I-III) is reported. In one-pot reactions of L with Cu(CH3CN)4PF6 in the absence (route I) and presence (route II) of CdI2, a cyclic dimer CuI complex, [Cu2(L)2](PF6)2 (1), and a one-dimensional coordination polymer, [Cu2(L)2]n·n[CdI4] (2), were obtained, respectively. Interestingly, the complex cations in 1 and 2 are supramolecular isomers formed via cyclization and polymerization upon complexation, respectively, probably due to different geometric and electronic complementarities, via the C-H···X- hydrogen bonds, between L and the counterion. In the two-step reaction (route III), an endocyclic Cd2+ complex, [Cd(L)I2] (3), obtained in the first step was utilized in the following reaction with Cu(CH3CN)4PF6, giving rise to an endo/exocyclic tetranuclear Cu+ complex, [Cu4(L)2(CH3CN)6](PF6)4 (4), via Cd2+ → 2Cu+ substitution, which is not accessible by conventional procedures. Solution studies by comparative NMR and electrospray ionization mass spectroscopy also support metal substitution by showing the stronger binding affinity of Cu+ over Cd2+. These results demonstrate that the metal substitution protocol could be useful for reaching novel metallosupramolecules difficult to obtain by other methods.

In this study, we report the synthesis and the equilibrium, kinetic, relaxation, and structural properties of two new GdIII complexes based on modified 10-(2-hydroxypropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (HPDO3A) designed to modulate the relaxivity at acidic and basic pH due to intra- and intermolecular proton exchange. The presence of a carboxylic or ester moieties in place of the methyl group of HPDO3A allowed differentiation of a protic and nonprotic functional group, highlighting the importance of the formation of an intramolecular hydrogen bond between the coordinated hydroxyl and the carboxylate groups for proton exchange (kH = 1.5 × 1011 M–1 s–1, kOH = 1.7 × 109 M–1 s–1). The determination of the thermodynamic stability and kinetic inertness of the GdIII complexes confirmed that the modification of peripheral groups does not significantly affect the coordination environment and thus the stability (log KGdL = 19.26, t1/2 = 2.14 × 107 hours, pH = 7.4, 0.15 M NaCl, 25 °C). The relaxivity (r1) was measured as a function of pH to investigate the proton exchange kinetics, and as a function of the magnetic field strength to extrapolate the relaxometric parameters (r1GdL1 = 4.7 mM–1 s–1 and r1GdL2 = 5.1 mM–1 s–1 at 20 MHz, 25 °C, and pH 7.4). Finally, the X-ray crystal structure of the complex crystallized at basic pH showed the formation of a tetranuclear dimer with alkoxide and hydroxide groups bridging the GdIII ions., The peripheral carboxylic moiety of a 2-hydroxypropanoic pendant arm of a GdHPDO3A-like complex forms an intramolecular hydrogen bond with the −OH group that allows both acid- and base-catalyzed proton exchange and thus a relaxivity enhancement. Conversely, the nonprotic ester group in the same position permits only the base-catalyzed mechanism.

Four inorganic-organic hybrid octa-Cu cluster sandwiched polyoxotungstates (POTs), [Cu8(H2O)2(en)4(B-α-H2SiW9O34)2] (1), [Cu8(H2O)2(en)4(B-α-H2GeW9O34)2] (2), K2[Cu8(en)4(B-α-HSiW9O34)2]·6H2O (3), and K2[Cu8(en)4(B-α-HGeW9O34)2]·2H2O (4) (en = ethylenediamine), were hydrothermally made and characterized by single-crystal X-ray diffraction, infrared spectra, powder X-ray diffraction, and thermogravimetric analysis, respectively. Structure analysis reveals that the polyoxoanion of 1/2 is a discrete dimer built by two trivalent Keggin [B-α-XW9O34]10- (X = Si/Ge) fragments and one octa-Cu cluster, whereas 3 and 4 display a two-dimensional network built by octa-Cu-sandwiched POT units via substitution of coordinated water on polyanions of 1 and 2 and further expand into a three-dimensional framework via K cation bridges. Ultraviolet-visible diffuse reflectance spectra reveal that 1-4 are potential semiconductor materials. Moreover, its visible light-driven catalytic H2 evolution activity, electrochemical properties, catalysis for oxygenation reactions of thioethers, and magnetic behaviors have been investigated in detail.

The zwitterionic ring-opening polymerization of N-functionalized eight-membered cyclic carbonates with N-heterocyclic carbenes (NHC) in the absence of alcohol initiators generates cyclic polycarbonates of Mn ∼ 30–100 kDa. The polymerization behavior of these eight-membered cyclic azacarbonates depends sensitively on the nature of the nitrogen substituent. The N-benzyl-substituted eight-membered cyclic carbonate (8CCBn) polymerizes readily with 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene to generate cyclic polycarbonates with molecular weights of Mn = 14 000 to 96 000 Da. In contrast, the N-phenyl-substituted cyclic carbonate (8CCPh) catalytically dimerizes in the presence of the NHC to afford the crystalline cyclic dimer. The zwitterionic ring-opening copolymerization of δ-valerolactone (VL) and the cyclic carbonates afford gradient cyclic copolymers. The cyclic topology of both the homopolymers and copolymers was supported by MALDI-TOF MS and intrinsic viscosity measurements. 13C NMR and differential ...

A near-infrared (NIR) light induced controlled cationic polymerization is presented here. The halide abstraction reaction between the cyclopentadienyl iron dicarbonyl dimer (Fe2(Cp)2(CO)4) and an o...

Refluxing Mo(CO)6 in the presence of the phosphine-functionalized α-diimine ligand Ph2PPrDI allowed for substitution and formation of the dicarbonyl complex, (Ph2PPrDI)Mo(CO)2. Oxidation with I2 followed by heating resulted in further CO dissociation and isolation of the corresponding diiodide complex, (Ph2PPrDI)MoI2. Reduction of this complex under a N2 atmosphere afforded the corresponding bis(dinitrogen) complex, (Ph2PPrDI)Mo(N2)2. The solid-state structures of all three compounds were found to feature a tetradentate chelate and cis-monodentate ligands. Notably, the addition of CO2 to (Ph2PPrDI)Mo(N2)2 is proposed to result in head-to-tail CO2 coupling to generate the corresponding metallacycle and ultimately a mixture of (Ph2PPrDI)Mo(CO)2 and the bis(oxo) dimer, [(κ3-Ph2PPrDI)Mo(O)(μ-O)]2. Computational studies have been performed to gain insight into the reaction and evaluate the importance of cis-coordination sites for selective head-to-tail CO2 reductive coupling, CO deinsertion, disproportionation, and stepwise CO2 deinsertion.

While the chemistry of trivalent rare-earth metal hydrido complexes has been well developed in the past 40 years, that of the divalent rare-earth metal hydrido complexes remains in its infancy because of the synthetic challenge of such complexes. In this paper, we report the synthesis and structural characterization of a divalent ytterbium hydrido complex supported by a bulky β-diketiminato-based tetradentate ligand. This hydrido complex is a dimer containing two μ-hydrogen ligands, and it easily undergoes a hydrido shift reaction to form a new divalent ytterbium hydrido complex that contains only one hydrido bridge. Furthermore, this hydrido complex reacts with pyridine and pyridine derivatives, showing versatile reactivity [Yb-H addition to pyridine, hydrido shift to ancillary ligand, and ytterbium(II)-center-induced redox reaction with bipyridine]. This hydrido complex reacts with Ph3P═O, resulting in a P-CPh cleavage of Ph3P═O and an elimination of C6H6; on the other hand, the reaction with Ph3P═S is a hydrido coupling-based redox reaction. The reactions of this hydrido complex with 1 and 2 equiv of PhSSPh clearly indicate that the hydrido coupling-based redox reaction is prior to the ytterbium(II) oxidation-based redox reaction.

Two crystalline diastereomorphs of rac-1-benzyl-3-bromo-5-hydroxy-4-[(4-methylphenyl)sulfanyl]-1,5-dihydro-2Н-pyrrole-2-one are obtained and characterized: the racemic compound (P21/c) and the normal conglomerate (P65, P61). The conglomerate is shown to be more thermodynamically preferred while the racemic compound is a metastable form in the entire temperature range studied. These two modifications are formed as a mixture during routine crystallization from a solution and characterized by a similar density, however, their structures significantly differ in the parameters of hydrogen bonds. A small difference in the free energies of two phases at room temperature, which is found by differential scanning calorimetry, explains the experimental availability of both forms during crystallization from the solution. The formation of a stronger hydrogen bond in the conglomerate crystals, which is detected by X-ray diffraction and solid-state vibrational spectroscopy, may be explained by a more favorable arrangement of donor and acceptor groups of the neighboring molecules in a homochiral helix of the conglomerate as compared with a heterochiral dimer, which is the main motif in crystals of the racemic compound.

Solid-state structures find a self-assembled tetrameric nickel cage with carboxylate linkages, [Ni(N2S'O)I(CH3CN)]4 ([Ni-I]40), resulting from sulfur acetylation by sodium iodoacetate of an [NiN2S]22+ dimer in acetonitrile. Various synthetic routes to the tetramer, best described from XRD as a molecular square, were discovered to generate the hexacoordinate nickel units ligated by N2Sthioether, iodide, and two carboxylate oxygens, one of which is the bridge from the adjacent nickel unit in [Ni-I]40. Removal of the four iodides by silver ion precipitation yields an analogous species but with an additional vacant coordination site, [Ni-Solv]+, a cation but with coordinated solvent molecules. This also recrystallizes as the tetramer [Ni-Solv]44+. In solution, dissociation into the (presumed) monomer occurs, with coordinating solvents occupying the vacant site [Ni(N2S'O)I(solv)]0, ([Ni-I]0). Hydrodynamic radii determined from 1H DOSY NMR data suggest that monomeric units are present as well in CD2Cl2. Evans method magnetism values are consistent with triplet spin states in polar solvents; however, in CD2Cl2 solutions no paramagnetism is evident. The abilities of [Ni-I]40 and [Ni-Solv]44+ to serve as sources of electrocatalysts, or precatalysts, for the hydrogen evolution reaction (HER) were explored. Cyclic voltammetry responses and bulk coulometry with gas chromatographic analysis demonstrated that a stronger acid, trifluoroacetic acid, as a proton source resulted in H2 production from both electroprecatalysts; however, electrocatalysis developed primarily from uncharacterized deposits on the electrode. With acetic acid as a proton source, the major contribution to the HER is from homogeneous electrocatalysis. Overpotentials of 490 mV were obtained for both the solution-phase [Ni-I]0 and [Ni-Solv]+. While the electrocatalyst derived from [Ni-Solv]+ has a substantially higher TOF (102 s-1) than [Ni-I]0 (19 s-1), it has a shorter catalytically active lifespan (4 h) in comparison to [Ni-I]0 (>18 h).

Available data on speciation of silica in aqueous solutions show that the main forms of silica are the monomer Si(OH)4 and the dimer Si2O(OH)6, with shares of higher polymers growing with an increa...

Reaction of 1 equiv of KN(SiMe3)2 with 9-fluorenone results in the formation of (Me3Si)N═C13H8 (1) in high yield after work-up. Addition of 1 equiv of phenol to 1 results in rapid desilylation and formation of 9-fluorenone imine, HN═C13H8 (2). Subsequent reaction of 2 with 1 equiv of LiNiPr2 results in deprotonation and formation of [Li(Et2O)]4[N═C13H8]4 (3) in good yield. Reaction of 1 equiv of KN(SiMe3)2 with 2-adamantanone for 7 days at room temperature results in the formation of (Me3Si)N═C10H14 (4) in good yield. Dissolution of 4 in neat MeOH results in rapid desilylation concomitant with formation of 2-adamantanone imine, HN═C10H14 (5). Subsequent reaction of 5 with 1 equiv of LiNiPr2 results in formation of [Li(THF)]4[N═C10H14]4 (6). Both 3 and 6 were characterized by X-ray crystallography. Finally, reaction of CrCl3 with 3.5 equiv of 6 results in formation of the [Cr2]6+ dimer, [Li][Cr2(N═C10H14)7] (7), which can be isolated in modest yield after work-up. Complex 7 features a Cr-Cr bond length of 2.653(2) A. Additionally, solid-state magnetic susceptibility measurements reveal strong antiferromagnetic coupling between the two Cr centers, with J = -200 cm-1.

Herein, we present the first example of the activation of small molecules by P–B–P bond systems. The reactivity study involves reactions of two selected diphosphinoboranes, (t-Bu2P)2BPh (1′) and (Cy2P)2BNiPr2 (2), that differ in terms of their structural and electronic properties for the activation of dihydrogen, carbon dioxide, and phenyl isocyanate. Diphosphinoborane 1′ activates H2 under very mild conditions in the absence of a catalyst with the formation of the dimer (t-Bu2PB(Ph)H)2 and t-Bu2PH. Conversely, diphosphinoborane 2 did not react with H2 under the same conditions. The reaction of 1′ with CO2 led to the formation of a compound with an unusual structure, where two phosphinoformate units were coordinated to the PhBOBPh moiety. In addition, 2 reacted with CO2 to insert two CO2 molecules into the P–B bonds of the parent diphosphinoborane. Both diphosphinoboranes activated PhNCO, yielding products resulting from the addition of two and/or three PhNCO molecules and the formation of new P–C, B–O, B–N, and C–N bonds. The products of the activation of small molecules by diphosphinoboranes were characterized with nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy, single-crystal X-ray diffraction, and elemental analysis. Additionally, the reaction mechanisms of the activation of small molecules by diphosphinoboranes were elucidated by theoretical methods., The first example of the activation of dihydrogen, carbon dioxide, and phenyl isocyanate by diphosphinoboranes is presented.

Protocatechuate 4,5-dioxygenase (LigAB) is a heterodimeric enzyme that catalyzes the dioxygenation of multiple lignin derived aromatic compounds. The active site of LigAB is at the heterodimeric interface, with specificity conferred by the alpha subunit and catalytic residues contributed by the beta subunit. Previous research has indicated that the phenylalanine at the 103 position of the alpha subunit (F103α) controls selectivity for the C5 position of the aromatic substrates, and mutations of this residue can enhance the rate of catalysis for substrates with larger functional groups at this position. While several of the mutations to this position (Valine, V; Threonine, T; Leucine, L; and Histidine, H) were catalytically active, other mutations (Alanine, A; and Serine, S) were found to have reduced dimer interface affinity, leading to challenges in copurifing the catalytically active enzyme complex under high salt conditions. In this study, we aimed to experimentally and computationally interrogate residues at the dimer interface to discern the importance of position 103α for maintaining the integrity of the heterodimer. Molecular dynamic simulations and electrophoretic mobility assays revealed a preference for nonpolar/aromatic amino acids in this position, suggesting that while substitutions to polar amino acids may produce a dioxygenase with a useful substrate utilization profile, those considerations may be off-set by potential destabilization of the catalytically active oligomer. Understanding the dimerization of LigAB provides insight into the multimeric proteins within the largely uncharacterized superfamily and characteristics to consider when engineering proteins that can degrade lignin efficiently. These results shed light on the challenges associated with engineering proteins for broader substrate specificity.

Dipeptide complexes of β-alanyl-histidine (carnosine) and β-alanyl-1-methyl-histidine (anserine) with the sodium dodecyl sulfate dimer (SDS)2 are studied by the DFT/B97D quantum chemical method using the 6-311++G(3d,3p) basis set. The most stable configurations of peptide complexes in cationic and zwitterionic forms with the (SDS)2 dimer are found. The changes in peptide structures and energies as a result of the complexation are analyzed. It is shown that both ionic forms of carnosine can participate in the reaction with the SDS dimer in aqueous solution. The influence of the methyl substituent in the imidazole ring of anserine is noticeably manifested in the lengths of H-bonds formed by the $$\text{NH}^+_3$$ group of the peptide with SDS due to high steric barriers encountered by the substituted peptide as it adjusts to the dimer structure. The complexation energies have close values for anserine and carnosine cations.

The synthesis and structural characterization of the monohydrated 1:2 cocrystal salt of acriflavine with 3,5-dinitrobenzoic acid [systematic name: 3,6-diamino-10-methylacridin-10-ium 3,5-dinitrobenzoate–3,5-dinitrobenzoic acid–water (1/1/1), C14H14N3 +·C7H3N2O6 −·C7H4N2O6·H2O] are reported. Single-crystal X-ray diffraction measurements show that the title solvated monohydrate salt crystalizes in the monoclinic space group P21 with one acriflavine cation, a 3,5-dinitrobenzoate anion, a 3,5-dinitrobenzoic acid molecule and a water molecule in the asymmetric unit. The neutral and anionic forms of 3,5-dinitrobenzoic acid are linked via O—H...O hydrogen bonds to form a monoanionic dimer. Neighbouring monoanionic dimers of 3,5-dinitrobenzoic acid are linked by nitro–nitro N—O...N and nitro–acid N—O...π intermolecular interactions to produce a porous organic framework. The acriflavine cations are linked with carboxylic acid molecules directly via amine–carboxy N—H...O, amine–nitro N—H...O and acriflavine–carboxy C—H...O hydrogen bonds, and carboxy–acriflavine C—O...π, nitro–acriflavine N—O...π and acriflavine–nitro π–π interactions, or through the water molecule by amino–water N—H...O and water–carboxy O—H...O hydrogen bonds, and are located in the voids of the porous organic framework. The intermolecular interactions were studied using the CrystalExplorer program to provide information about the interaction energies and the dispersion, electrostatic, polarization and repulsion contributions to the lattice energy.

Green colored mononuclear copper(II) complexes viz. [Cu(L)(bpy)](ClO4) (1) or [Cu(L)(phen)](ClO4) (2) (where H(L) is 2-((2-dimethylamino)ethyliminomethyl)naphthol) show distorted square pyramidal (4 + 1) geometry with CuN4O chromophore. The existence of self-assembled molecular associations indicates the formation of the dimer. Dimeric nature in solution is retained due to the binding of the substrate, encourages steric match between substrate and Cu(II) active site, which favors electron transfer. Interestingly, both the complexes exhibit high-positive redox potential. Therefore, the presence of self-assembled molecular association along with the positive redox potential enhances the catalytic oxidation of ascorbic acid to dehydroascorbic acid or benzylamine to benaldehyde or catechol to o-quinone thereby model the functional properties of type 2 and type 3 copper oxidases. Notably, catalytic activity is effective when compared with other reported mononuclear copper(II) complexes and even superior to many binuclear copper(II) complexes. Existence of self-assembled molecular association in solution along with high-positive redox potential favors electron transfer process in mononuclear copper(II) complexes and models the functional properties of type 2 and type 3 copper oxidases.

Efficient and selective electrochemical reduction of CO2 is a promising approach for its conversion to high value-added chemicals and reducing its green-house effect. Unless a suitable catalyst is used, the reduction occurs at a high overpotential (η) and generates versatile products. Here a novel flexible cofacial Fe perfluorinated porphyrin dimer, f-Fe2PD, was designed for the electrocatalytic CO2-to-CO conversion in nonaqueous and aqueous solutions. The f-Fe2PD showed the CO2-to-CO conversion starting at only η = 0.15 V that is the lowest reported overpotential in a homogeneous CO2-saturated DMF/10% H2O/1.0 M PhOH solution. This η value is 0.29 V lower than that (0.44 V) of the corresponding rigid cofacial Fe porphyrin dimer (r-Fe2PD). The f-Fe2PD exhibited extremely high turnover frequencies (log TOF) of 2.4 and 7.3 s−1 at η values of 0.26 and 0.46 V, respectively with >94% CO faradaic efficiency (FECO). Moreover, the dimer was immobilized on ketjen black carbon (KBC) and grafted on a glassy carbon (GC) surface to achieve efficient and selective CO2-to-CO conversion in neutral aqueous CO2-saturated NaHCO3 solutions (0.5 M, pH = 7.3) with high durability. f-Fe2PD/KBC@GC showed TOF values of 4.5 and 18.1 s−1 with practical current densities of 3.1 and 12.8 mA cm−2 at η values of 0.26 and 0.46 V, respectively. These values, to the best of our knowledge, are the highest reported values achieved in aqueous solutions at such low and moderate η values. Several post-operando measurements proved the integrity of the f-Fe2PD under the CO2-to-CO conversion conditions. The combination of activity, efficiency, durability, and selectivity of the f-Fe2PD particularly in aqueous solutions is promising for clean energy production.

[RuCp*(1,3,5-R3C6H3)]2 {Cp* = η5-pentamethylcyclopentadienyl, R = Me, Et} have previously been found to be moderately air stable, yet highly reducing, with estimated D+/0.5D2 (where D2 and D+ represent the dimer and the corresponding monomeric cation, respectively) redox potentials of ca. −2.0 V vs. FeCp2+/0. These properties have led to their use as n-dopants for organic semiconductors. Use of arenes substituted with π-electron donors is anticipated to lead to even more strongly reducing dimers. [RuCp*(1-(Me2N)-3,5-Me2C6H3)]+PF6− and [RuCp*(1,4-(Me2N)2C6H4)]+PF6− have been synthesized and electrochemically and crystallographically characterized; both exhibit D+/D potentials slightly more cathodic than [RuCp*(1,3,5-R3C6H3)]+. Reduction of [RuCp*(1,4-(Me2N)2C6H4)]+PF6− using silica-supported sodium–potassium alloy leads to a mixture of isomers of [RuCp*(1,4-(Me2N)2C6H4)]2, two of which have been crystallographically characterized. One of these isomers has a similar molecular structure to [RuCp*(1,3,5-Et3C6H3)]2; the central C–C bond is exo,exo, i.e., on the opposite face of both six-membered rings from the metals. A D+/0.5D2 potential of −2.4 V is estimated for this exo,exo dimer, more reducing than that of [RuCp*(1,3,5-R3C6H3)]2 (−2.0 V). This isomer reacts much more rapidly with both air and electron acceptors than [RuCp*(1,3,5-R3C6H3)]2 due to a much more cathodic D2˙+/D2 potential. The other isomer to be crystallographically characterized, along with a third isomer, are both dimerized in an exo,endo fashion, representing the first examples of such dimers. Density functional theory calculations and reactivity studies indicate that the central bonds of these two isomers are weaker than those of the exo,exo isomer, or of [RuCp*(1,3,5-R3C6H3)]2, leading to estimated D+/0.5D2 potentials of −2.5 and −2.6 V vs. FeCp2+/0. At the same time the D2˙+/D2 potentials for the exo,endo dimers are anodically shifted relative to those of [RuCp*(1,3,5-R3C6H3)]2, resulting in much greater air stability than for the exo,exo isomer.

The novel complex [FeIIICl(L)2(H2O)] (1) was synthesized by interaction of iron(III) chloride with ethanol solution of o-vanillin (HL) and characterized by IR, UV/Vis spectroscopy, thermogravimetry and single crystal X-ray diffraction analysis. The molecules of 1 in the solid state are joined into supramolecular dimeric units, where a set of strong hydrogen bonds predefines the structure of the dimer according to the “key-lock” principle. From the Hirshfield surface analysis the contribution of π⋯π stacking to the overall stabilization of the dimer was found to be negligible. Broken symmetry DFT calculations suggested the presence of long-range antiferromagnetic interactions (J = −0.12 cm−1 for H = −JS1S2 formalism) occurring through the Fe–O⋯O–Fe pathway, as evidenced by the studies of the model dimers where the water molecules were substituted by acetonitrile and acetone ones. The benchmark studies using a set of literature examples and various DFT functionals revealed the hybrid-GGA B3LYP as the best one for prediction of FeIII⋯FeIII antiferromagnetic exchange couplings of small magnitude. Magnetic susceptibility measurements confirmed antiferromagnetic coupling between the metal atoms in 1 with a coupling constant of −0.35 cm−1. Catalytic studies demonstrated that 1 acts as an efficient catalyst in the oxidation of cyclohexane with hydrogen peroxide in the presence of nitric acid promoter and under mild conditions (yield up to 37% based on the substrate), while tert-butylhydroperoxide (TBHP) and m-chloroperoxybenzoic acid (m-CPBA) as oxidants exhibit less efficiency. Combined UV/TDDFT studies evidence the structural rearrangement of 1 in acetonitrile with the formation of [FeIIICl(L)2(CH3CN)] species. The TDDFT benchmark using nine common DFT functionals and two model compounds (o-vanillin and [FeIII(H2O)6]3+ ion) support the hybrid meta-GGA M06-2X functional as the one most correctly predicting the excited state structure for the Fe(III) complexes, under the conditions studied.

A new birefringent crystal SbB5O9 has been synthesized by combining π-conjugated [B3O6] groups and Sb3+ cations with SCALP. It exhibits the unwonted [B5O11] fundamental building block (FBB) and dimeric [Sb2O6] cluster. Remarkably, SbB5O9 exhibits a short UV cutoff edge (below 240 nm) and a large birefringence (Δn = 0.151 @ 1064 nm) which is even better than that of the well-known commercial birefringent material α-BaB2O4 (α-BBO) (Δn = 0.122 @ 532 nm). First-principles calculations show that the birefringence enhancement mainly originates from the highly distorted [Sb2O6] dimer and π-conjugated B–O anionic groups.

In this work, six Pt(II) complexes based on 4,4′-bis(triethylsilylethynyl)-2,2′-bipyridine ligand were designed and synthesized. The crystal structures of complexes 1, 2, 5 and 6 showed that these complexes adopt dimer structures with ultra-short intermolecular Pt⋯Pt distances [3.1674(4)–3.1973(7) A]. In the solid state, all complexes exhibited long-wavelength NIR luminescence with maximum emission centered at 1045 nm for 1, 1062 nm for 2, 939 nm for 3, 1051 nm for 4, 1037 nm for 5, and 1029 nm for 6. This is the first report on the Pt(II) dimer with luminescence exceeding 1000 nm. More importantly, 1062 nm of complex 2 is the longest emission wavelength of the reported 2,2′-bipyridyl-platinum(II) complex. Furthermore, these complexes also exhibited reversible mechanoluminescence property. Systematic studies on the crystal structure, photophysical properties and PXRD patterns revealed that the long-wavelength NIR luminescence of dimers is due to the enhanced MMLCT transitions, and the mechanism of reversible mechanoluminescence property involves changes in the strength of the Pt–Pt interaction caused by reversible alteration of intermolecular Pt⋯Pt distances during the mechanical grinding-vapor absorbing process.

Iron hexamesityl-5,15-diazaporphyrin was synthesized through the cross-coupling reaction of tetrabromodiazaporphyrin. The use of chloroiron(III) hexamesityl-5,15-diazaporphyrin as a catalyst for oxidation of cyclooctane showed high performance with a total TON up to 731. The introduction of bulky mesityl groups at β-positions prevented the catalyst deactivation via formation of a μ-oxo dimer.

A new ruthenium polypyridyl complex, [Ru(bpy)2(acpy)]+ (acpy = 2-pyridylacetate, bpy = 2,2′-bipyridine), was synthesized and fully characterized. Distinct from the previously reported analog, [Ru(bpy)2(pic)]+ (pic = 2-pyridylcarboxylate), the new complex is unstable under aerobic conditions and undergoes oxidation to yield the corresponding α-keto-2-pyridyl-acetate (acpyoxi) coordinated to the RuII center. The reaction is one of the few examples of C–H activation at mild conditions using O2 as the primary oxidant and can provide mechanistic insights with important implications for catalysis. Theoretical and experimental investigations of this aerobic oxidative transformation indicate that it takes place in two steps, first producing the α-hydroxo-2-pyridyl-acetate analog and then the final product. The observed rate constant for the first oxidation was in the order of 10−2 h−1. The reaction is hindered in the presence of coordinating solvents indicating the role of the metal center in the process. Theoretical calculations at the M06-L level of theory were performed for multiple reaction pathways in order to gain insights into the most probable mechanism. Our results indicate that O2 binding to [Ru(bpy)2(acpy)]+ is favored by the relative instability of the six-ring chelate formed by the acpy ligand and the resulting RuIII-OO˙− superoxo is stabilized by the carboxylate group in the coordination sphere. C–H activation by this species involves high activation free energies (ΔG‡ = 41.1 kcal mol−1), thus the formation of a diruthenium μ-peroxo intermediate, [(RuIII(bpy)2(O-acpy))2O2]2+via interaction of a second [Ru(bpy)2(acpy)]+ was examined as an alternative pathway. The dimer yields two RuIVO centers with a low ΔG‡ of 2.3 kcal mol−1. The resulting RuIVO species can activate C–H bonds in acpy (ΔG‡ = 23.1 kcal mol−1) to produce the coordinated α-hydroxo-2-pyridylacetate. Further oxidation of this intermediate leads to the α-keto-2-pyridyl-acetate product. The findings provide new insights into the mechanism of C–H activation catalyzed by transition-metal complexes using O2 as the sole oxygen source.

Exposure of 10π-electron benzazaphosphole 1 to HCl, followed by nucleophilic substitution with the Grignard reagent BrMgCCPh afforded alkynyl functionalized 3 featuring an exocyclic -C[triple bond, length as m-dash]C-Ph group with an elongated P-C bond (1.7932(19) Å). Stoichiometric experiments revealed that treatment of trans-Pd(PEt3)2(Ar)(i) (Ar = p-Me (C) or p-F (D)) with 3 generated trans-Pd(PEt3)2(Ar)(CCPh) (Ar = p-Me (E) or p-F (F)), 5, which is the result of ligand exchange between P-I byproduct 4 and C/D, and the reductively eliminated product (Ar-C[triple bond, length as m-dash]C-Ph). Cyclic voltammetry studies showed and independent investigations confirmed 4 is also susceptible to redox processes including bimetallic oxidative addition to Pd(0) to give Pd(i) dimer 6-Pd2-(P(t-Bu)3)2 and reduction to diphosphine 7. During catalysis, we hypothesized that this unwanted reactivity could be circumvented by employing a source of fluoride as an additive. This was demonstrated by conducting a Sonogashira-type reaction between 1-iodotoluene and 3 in the presence of 10 mol% Na2PdCl4, 20 mol% P(t-Bu)Cy2, and 5 equiv. of tetramethylammonium fluoride (TMAF), resulting in turnover and the isolation of Ph-C[triple bond, length as m-dash]C-(o-Tol) as the major product.

Pd complexes [Pd(P∩P)(4-Sepy)2] of 4-pyridylselenolate (4-Sepy) and diphosphines (P∩P = dppe (1,2-bis(diphenylphosphino)ethane), dppf (1,1′-bis(diphenylphosphino)ferrocene) and Xantphos (4,5-bis(diphenylphosphino)-9,9-dimethylxanthene)) have been developed as metallo-ligands. Their self-assembly reaction with [Pd(P∩P)(OTf)2] (OTf− = CF3SO3−) successfully yielded the cationic macrocyclic complexes [Pd(P∩P)(4-Sepy)]n(OTf)n. The major and minor products are assigned to the dimer (n = 2) and tetramer (n = 4) by nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry and X-ray structural analysis. The equilibrium between the dimer and tetramer has been established in compounds of wide-bite-angle dppf. The same reaction for Xantphos as diphosphine produced a selenolato-bridged trinuclear complex with a free pyridyl group. A similar reaction with analogous 4-mercaptopyridine resulted in a mononuclear complex of Xantphos comprising Pd–O bond. Density functional theory calculations establish the stability of the macrocycles as tetranuclear (dppf) > dinuclear (dppf) > dinuclear (dppe). A low energy charge transfer transition has been identified from Se or Fe centers to unoccupied orbitals of mixed character. These macrocycles represent the first examples of metallo-supramolecular complexes constructed from selenolate groups and square-planar metal ions. The Pd complexes showed excellent catalytic activity with high turnover numbers (5 × 107) in Suzuki C–C cross coupling reactions.

N-Heterocyclic carbene (NHC) ligands support gold(I) sulfide complexes of varying nuclearity and charge. For sterically undemanding ligands, gold(I) chlorides react with sulfide to form trigold μ3-sulfido cations as the first observed products. The ligand IMes [1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] supports a monomeric cation, whereas the ICy-(1,3-dicyclohexylimidazol-2-ylidene-) supported cation crystallises as a dimer linked through an aurophilic interaction. The more sterically demanding IDipp [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene] supports a terminal hydrosulfide, a (μ-hydrosulfido)digold cation, and a μ3-sulfido cation. Use of the expanded-ring NHC 7Dipp [1,3-bis(2,6-diisopropylphenyl)-4,5,6,7-tetrahydro-1,3-diazepin-2-ylidene] allows the isolation of a neutral digold sulfide.

Herein, we report the synthesis of a monocationic μ-nitrido-bridged iron porphycene dimer, a structural analogue of a monocationic μ-nitrido-bridged iron phthalocyanine dimer, which is known to be one of the most potent molecule-based catalysts for methane oxidation. 1H-NMR and single-crystal X-ray structural analyses showed that the porphycene complex includes two Fe(IV) ions, and the structure around the Fe–NFe core is quite similar to that of the monocationic μ-nitrido-bridged iron phthalocyanine dimer. Although methane was oxidized into MeOH, HCHO, and HCOOH in the presence of a silica-supported catalyst of this monocationic μ-nitrido-bridged iron porphycene dimer in an acidic aqueous solution containing excess H2O2, its reactive intermediate was not a high-valence iron-oxo species, as in the case of a monocationic μ-nitrido-bridged iron phthalocyanine dimer, but ˙OH. It is suggested that the high-valent iron-oxo species of the μ-nitrido-bridged iron porphycene dimer was gradually decomposed under these reaction conditions, and the decomposed compound catalyzed a Fenton-type reaction. This result indicates that the stability of the oxo-species is indispensable for achieving high catalytic methane oxidation activity using a μ-nitrido-bridged iron porphyrinoid dimer with an Fe–NFe core as a catalyst.

The reactions of K2ZnSb (0.234 mol) and Ni(CO)2(PPh3)2 (x mol) in ethylenediamine (en) solutions of 18-crown-6 at 60 °C yielded half-centered [Ni0.5@{Sb6Ni6(CO)8}]4− (x = 0.023, 1) and fully embedded [Ni@{Sb7Ni5(CO)6}]3− (x = 0.047, 2), wherein the chair-like Sb6 subunit is bicapped by two Ni3 triangles to form the single Sb6Ni6 icosahedron of 1 and by the triangular Ni2Sb and Ni3 to form the single Sb7Ni5 icosahedron of 2. Surprisingly, a smaller amount of Ni(CO)2(PPh3)2 (x = 0.016) led to the formation of the unprecedented dimer [(Sb8){Sb7Ni5(CO)4}2]6− (4), wherein the Sb7Ni5 icosahedral unit built of boat-like Sb6, Ni2Sb and Ni3 is linked together by the realgar-like Sb8 to form the icosahedral dimer 4, providing a new way of thinking for the preparation of icosahedral oligomers/polymers. A similar hexa-anionic dimer (3) can be solely obtained using PBu4+ as the countercation under the same reaction conditions. The structure and bonding of this novel series of icosahedral clusters containing polyantimony were discussed for the first time.

Ligand H2LAP comprises a non-innocent 2-aminophenol unit and an innocent bis(pyridin-2-ylmethyl)amine unit. The ligand, upon reaction with an equivalent amount of Mn(ClO4)2·6H2O in the presence of Et3N under air in MeOH, provided a mono(oxo)-bridged dinuclear Mn2 complex ({[(LISQ)MnIII-O-MnIII(LISQ)][(ClO4)]2}; 1). X-ray crystal structure analysis of complex 1 revealed that in the dicationic unit, the physical oxidation state of each Mn ion was +III and the 2-aminophenol unit of ligand H2LAP was in its one-electron oxidized iminobenzosemiquinone form. 1H-NMR measurement of complex 1 confirmed that the complex acquired a diamagnetic ground state (St = 0). Thus, antiferromagnetic couplings among the paramagnetic centers were realized. The UV-Vis-NIR spectrum of complex 1 was consisted of ligand-to-metal charge-transfer transitions in the visible region, while ligand-to-metal and metal-to-ligand charge-transfer transitions were noticed in the near-infrared region due to the presence of iminobenzosemiquinone radical units. The cyclic voltammogram of the complex showed three one-electron oxidation waves and two one-electron reduction waves. While the first two oxidation processes were metal-based, the two successive reductions were ligand-centered. DFT-based theoretical studies confirmed the assignment.

Density functional theory computations revealed a pivalic acid assisted C–H bond activation mechanism for rhodium catalyzed formation of α-branched amines with C–C and C–N bond couplings. The reaction energies of the [Cp*RhCl2]2 dimer and silver cations indicate that the Cp*RhCl+ cation is the active catalyst. The essential role of pivalic acid is a co-catalyst for the activation of the ortho-C(sp2)–H bond in phenyl(pyrrolidin-1-yl)methanone, while the reaction of NaHCO3 and HCl reduces the overall barrier of the catalytic cycle. In the presence of both pivalic acid and NaHCO3 in the reaction, the C(sp2)–H bond is activated through a concerted metallation deprotonation process, and the C–C bond coupling is the rate-determining step with a total free energy barrier of 23.9 kcal mol−1. Without pivalic acid and NaHCO3, the C(sp2)–H bond can only be activated through a σ-bond metathesis process and the free energy barrier increases to 32.2 kcal mol−1. We also investigated the mechanisms of a side reaction for β-branched amine formation and the reaction without styrene and found that their free energy barriers are 33.4 and 30.5 kcal mol−1, respectively.

Polyoxometalate-based organic–inorganic hybrids have attracted considerable attention due to their fascinating structures and wide application prospects. In this work, using the same building blocks, ligands and metal ions (ZnW12O406−(ZnW12), 2,2′-bipyridine (2,2′-bipy), and Cu2+), we synthesized three new POM-based hybrids by controlling the pH values of the reaction systems. These three compounds {(Zn0.6(H2)0.4W12O40)[Cu(2,2′-bipy)(H2O)][Cu(2,2′-bipy)(H2O)2][Cu(2,2′-bipy)(H2O)3]}2·6H2O (1), (Me4N)2{ZnW12O40[Cu(2,2′-bipy)(H2O)][Cu(2,2′-bipy)(H2O)3]}·5H2O (2), and {(Zn0.5(H2)0.5W12O40)[Cu(2,2′-bipy)][Cu(2,2′-bipy)(H2O)][Cu(2,2′-bipy)(H2O)2]}·5H2O (3) have been structurally characterized by single-crystal X-ray diffraction. Compound 1 appears as a dimeric cluster structure, while compounds 2 and 3 appear as a 1D chain structure and a 2D network, respectively. The semiconducting properties of compounds 1–3 are different, which was demonstrated by band gap (Eg) and photocurrent response measurements. Compound 3 can efficiently catalyze the photooxidation of toluene to benzaldehyde with high selectivity using molecular oxygen as the oxidant component. Moreover, compound 3 was recycled and reused three times without significant degradation in conversion and selectivity. In addition, the mechanism of the photocatalytic reaction was also investigated.

The di(hydroperoxy)adamantane adducts of water (1) and phosphine oxides p-Tol3PO·(HOO)2C(C9H14) (2), o-Tol3PO·(HOO)2C(C9H14) (3), and Cy3PO·(HOO)2C(C9H14) (4), as well as a CH2Cl2 adduct of a phosphole oxide dimer (8), have been created and investigated by multinuclear NMR spectroscopy, and by Raman and IR spectroscopy. The single crystal X-ray structures for 1–4 and 8 are reported. The IR and 31P NMR data are in accordance with strong hydrogen bonding of the di(hydroperoxy)adamantane adducts. The Raman ν(O–O) stretching bands of 1–4 prove that the peroxo groups are present in the solids. Selected di(hydroperoxy)alkane adducts, in combination with AlCl3 as catalyst, have been applied for the direct oxidative esterification of n-nonyl aldehyde, benzaldehyde, p-methylbenzaldehyde, p-bromobenzaldehyde, and o-hydroxybenzaldehyde to the corresponding methyl esters. The esterification takes place in an inert atmosphere, under anhydrous and oxygen-free conditions, within a time frame of 45 minutes to 5 hours at room temperature. Hereby, two oxygen atoms per adduct assembly are active with respect to the quantitative transformation of the aldehyde into the ester.

Phosphinodiboranates (H3BPR2BH3−) are a class of borohydrides that have merited a reputation as weakly coordinating anions, which is attributed in part to the dearth of coordination complexes known with transition metals, lanthanides, and actinides. We recently reported how K(H3BPtBu2BH3) exhibits sluggish salt elimination reactivity with f-metal halides in organic solvents such as Et2O and THF. Here we report how this reactivity appears to be further attenuated in solution when the tBu groups attached to phosphorus are exchanged for R = Ph or H, and we describe how mechanochemistry was used to overcome limited solution reactivity with K(H3BPPh2BH3). Grinding three equivalents of K(H3BPPh2BH3) with UI3(THF)4 or LnI3 (Ln = Ce, Pr, Nd) allowed homoleptic complexes with the empirical formulas U(H3BPPh2BH3)3 (1), Ce(H3BPPh2BH3)3 (2), Pr(H3BPPh2BH3)3 (3), and Nd(H3BPPh2BH3)3 (4) to be prepared and subsequently crystallized in good yields (50–80%). Single-crystal XRD studies revealed that all four complexes exist as dimers or coordination polymers in the solid-state, whereas 1H and 11B NMR spectra showed that they exist as a mixture of monomers and dimers in solution. Treating 4 with THF breaks up the dimer to yield the monomeric complex Nd(H3BPPh2BH3)3(THF)3 (4-THF). XRD studies revealed that 4-THF has one chelating and two dangling H3BPPh2BH3− ligands bound to the metal to accommodate binding of THF. In contrast to the results with K(H3BPPh2BH3), attempting the same mechanochemical reactions with Na(H3BPH2BH3) containing the simplest phosphinodiboranate were unsuccessful; only the partial metathesis product U(H3BPH2BH3)I2(THF)3 (5) was isolated in poor yields. Despite these limitations, our results offer new examples showing how mechanochemistry can be used to rapidly synthesize molecular coordination complexes that are otherwise difficult to prepare using more traditional solution methods.

The interplay between noncovalent interactions involving metal complexes may lead to the formation of aggregates (i.e., ground state dimers, trimers, n-mers, etc.), and this is often linked to dramatic changes in their physical and chemical properties as compared to the original properties of the isolated units. Dimers and trimers can also be formed in the excited state potential energy surfaces, i.e., excimers. Excimers are short-lived but are also often characterized by different optical properties from those of the isolated units. Understanding the nature of noncovalent interactions and the presence or not of cooperativity effects in both aggregates and excimers is thus extremely important to rationalize these variations. In this study, we present computational investigations on isoquinolinyl pyrazolate Pt(II) complexes. Our results highlight that cooperativity effects between noncovalent interactions, which are modulated by sterically demanding substituents and metallophilic Pt···Pt interactions, are present only on certain investigated excimers. We use density functional theory (DFT) calculations to examine the cooperativity effects and the changes in the photophysical properties. Different descriptors of cooperativity effects between noncovalent interactions, including the synergetic, genuine nonadditive, and total interaction energies, were evaluated for a series of Pt(II) aggregates and excimers. In addition, energy decomposition analysis (EDA) calculations were performed to rationalize the origins of the cooperative effects. The cooperative effects in trimer excimers (in their lowest triplet excited state, i.e., T1) led to shortened Pt···Pt contacts as compared to the trimer aggregates. Furthermore, this synergy between noncovalent interactions is ultimately responsible for the formation of the excimers and the striking changes in the measured photophysical properties. More in detail, we report a change in the character of the lowest-lying triplet excited state when going from dimer excimers (i.e., of mixed triplet ligand-centered and triplet metal-to-ligand charge transfer (3LC/3MLCT) character) to trimer excimers (i.e., of triplet metal-metal-to-ligand charge transfer (3MMLCT) character). The EDA reveals that the total interaction energy on trimer excimers is subtly controlled by the electrostatic and dispersion terms. ispartof: INORGANIC CHEMISTRY vol:59 issue:24 pages:18253-18263 ispartof: location:United States status: published

Reversible photocycloaddition reactions have previously been employed in chemical cross-linking for the preparation of biomaterial scaffolds. However, the processes require activation by high-energy UV light, rendering them unsuitable for modification in biological environments. Here we demonstrate that the [2 + 2] photocycloaddition of styrylpyrene can be activated by visible light at λ = 400–500 nm, enabling rapid and effective conjugation and cross-linking of poly(ethylene glycol) (PEG) in water and under mild irradiation conditions (I = 20 mW cm–2). Notably, the reversion of the cycloaddition can be triggered by low-energy UV light at λ = 340 nm, which allows for efficient cleavage of the dimer adduct. Using this wavelength-gated reversible photochemical reaction we are able to prepare PEG hydrogels and modulate their mechanical properties in a bidirectional manner. We also demonstrate healing of the fractured hydrogel by external light triggers. Furthermore, we show that human mesenchymal stem cells ...