The tetranuclear iron(III) compounds [Fe(?-O)(?-L)] (1-3) were obtained by reaction of FeCl with the shortened salen-type NO tetradentate Schiff bases N,N'-bis(salicylidene)-o-Z-phenylmethanediamine HL (Z = NO, Cl and OMe, respectively), where the one-carbon bridge between the two iminic nitrogen donor atoms guide preferentially to the formation of oligonuclear species, and the ortho position of the substituent Z on the central phenyl ring selectively drives towards Fe bis-oxido clusters. All compounds show a flat almost-symmetric butterfly-like conformation of the {Fe(?-O)} core, surrounded by the four Schiff base ligands, as depicted by both the X-ray molecular structures of 1 and 2 and the optimized geometries of all derivatives as obtained by UM06/6-311G(d) DFT calculations. The strength of the antiferromagnetic exchange coupling constants between the iron(III) ions varies among the three derivatives, despite their magnetic cores remain structurally almost unvaried, as well as the coordination of the metal ions, with a distorted octahedral environment for the two-body iron ions, Fe, and a pentacoordination with trigonal bipyramidal geometry for the two-wing iron ions, Fe. The different magnetic behavior within the series of examined compounds may be ascribed to the influence of the electronic features of Z on the electron density distribution (EDD) of the central {Fe(?-O)} core, substantiated by a Quantum Theory of Atoms In Molecules (QTAIM) topological analysis of the EDD, as obtained by UM06 calculations 1-3.

The chemical industry needs to develop clean, efficient and selective procedures to synthesize high added-value fine chemicals and catalytic processes provide powerful tools to reach this goal. The key point to perform sustainable transformations is the choice of catalytic systems that show selectivity, activity and stability, resulting in high TOF (turnover frequency) and TON (turnover number), not to mention an efficient catalyst must be easily recovered and recycled. Based on these concepts, the employment of metal porphyrin complexes in catalysis is constantly growing due to the enormous potential of this class of molecules. Metal porphyrins are robust and their chemo-physical properties can easily be fine-tuned by varying their molecular structure to allow the use of these catalysts to selectively promote a large number of organic transformations. We have studied in depth the employment of metal porphyrin complexes to create new C-N and C-C bonds by using organic azides[1] and diazo compounds[2] and more recently we have focused our interest also on the synthesis of high-added value fine chemicals by using waste, such as CO2, as starting material by applying 100% atom economic procedures.[3] We will present different synthetic protocols which will also be discussed from a mechanistic point of view based on spectroscopic and theoretical studies and the identification of active intermediates. It is important to point out that mechanistic speculations are fundamental to optimize the catalytic performance of porphyrin complexes and spread out their applications in other fields of homogeneous catalysis

Platinum complexes are ubiquitous in chemistry and largely used as catalysts or as precursors in drug chemistry, thus a deep knowledge of their electronic properties may help in planning new synthetic strategies or exploring new potential applications. Herein, the electronic structure of many octahedral platinum complexes is drastically revised especially when they feature electronegative elements such as halogens and chalcogens. The investigation revealed that in most cases the five d platinum orbitals are invariably full, thus the empty antibonding orbitals, usually localized on the metal, are mainly centered on the ligands, suggesting a questionable assignment of formal oxidation state IV. The analysis supports the occurrence of the Inverted Ligand Field theory in all cases with the only exceptions of the Pt-F and Pt-O bonding. The trends for the molecular complexes are mirrored also by the Density of States plots of extended structures featuring octahedral platinum moieties in association with chalcogens atoms. Finally, the oxidative addition of a Se-Cl linkage to a square platinum complex to achieve an octahedral moiety has been revised in the framework of the Inverted Ligand Field.

This work describes a successful approach to dope copper sulfide with different amounts of Co2+ ions and combine it with TiO2 through a simple one-step hydrothermal process. Compared with the bare CuS, the syn-thesized Co-CuS@TiO2 heterostructures promote charge transport and restrict the recombination of photoexcited electrons and holes. The intrinsic properties of Co-CuS@TiO2 samples are systematically examined through experimental characterizations and density functional theory (DFT) theoretical calculations. Photocatalytic degradation tests under simulated solar light irradiation were performed using sulfamethoxazole degradation as a model emerging persistent antibiotic. The photocatalytic performance was enhanced after cobalt doping, and the heterostructure doped with 3% of Co exhibited the best degradation with an apparent rate constant of 0.0216 min-1. This sample also showed a much faster settling than bare TiO2, which indicates a much easier separation of the reaction media after being used. The enhancement of degradation is attributed to the increased light absorption and the more efficient charge transfer and separation. The plausible photocatalytic degradation mechanism of sulfamethoxazole was also proposed. This study presents a novel strategy to prepare potential photocatalysts for the elimination of emerging pollutants.

Luminescent solar concentrators (LSCs) are a class of optical devices able to harvest, downshift, and concentrate sunlight, thanks to the presence of emitting materials embedded in a polymer matrix. Use of LSCs in combination with silicon-based photovoltaic (PV) devices has been proposed as a viable strategy to enhance their ability to harvest diffuse light and facilitate their integration in the built environment. LSC performances can be improved by employing organic fluorophores with strong light absorption in the center of the solar spectrum and intense, red-shifted emission. In this work, we present the design, synthesis, characterization, and application in LSCs of a series of orange/red organic emitters featuring a benzo[1,2-b:4,5-b']dithiophene 1,1,5,5-tetraoxide central core as an acceptor (A) unit. The latter was connected to different donor (D) and acceptor (A') moieties by means of Pd-catalyzed direct arylation reactions, yielding compounds with either symmetric (D-A-D) or non-symmetric (D-A-A') structures. We found that upon light absorption, the compounds attained excited states with a strong intramolecular charge-transfer character, whose evolution was greatly influenced by the nature of the substituents. In general, symmetric structures showed better photophysical properties for the application in LSCs than their non-symmetric counterparts, and using a donor group of moderate strength such as triphenylamine was found preferable. The best LSC built with these compounds presented photonic (external quantum efficiency of 8.4 ± 0.1%) and PV (device efficiency of 0.94 ± 0.06%) performances close to the state-of-the-art, coupled with a sufficient stability in accelerated aging tests.

Low-temperature chemical vapor deposition (LT-CVD) of graphene using liquid aromatic hydrocarbons holds technological advantages over conventional growth from methane. However, the nature of decomposition mechanisms of such precursors and their effectiveness in a LT-CVD process is still debated. We investigate by means of density functional theory adsorption energies and decomposition first steps on Cu(111) of single-ring aromatic hydrocarbons, such as benzene and toluene. Our results confirm the stronger stability with respect to methane of aromatic adsorbates, due to exchange of London dispersion forces with Cu surface; however, toluene exhibits improved bindings with respect to benzene. The adsorption energy slightly improves if additional methyl groups are substituted in benzene, as in o-xylene and 1,2,3-trimethylbenzene. Among decomposition reactions, dehydrogenation of the methyl group in toluene is energetically more favored (1.20 eV) than that of methane (1.52 eV) or aromatic C-rings (1.67 eV and 1.72 eV for benzene and toluene), while demethylation of toluene remains negligible due to the prohibitive energy barrier (2.49 eV). Methyl dehydrogenation in toluene leads to the abundant formation of adsorbed benzyl radicals onto Cu in an almost parallel-to-surface configu-ration, as active species for graphene nucleation. Toluene (and to a lesser extent o-xylene and 1,2,3-trimethyl-benzene) should be thus preferred to benzene in LT-CVD of graphene.

A detailed computational analysis of the synthesis of thiazolidine-2-thiones by the CS2 insertion into the three membered aziridine rings is here reported. DFT studies highlighted the feasibility of the atom-efficient process by employing either the metal free binary TPPH2/TBACl system or bifunctional TPPH4Cl2 molecule as the catalytic species. Detailed investigations on the mechanism promoted by TPPH2/TBACl system indicated, as in the analogous cycloaddition of CO2, the pivotal role of adduct between TPPH2 and TBACl salt in the synthesis of both N-aryl and N-alkyl thiazolidine-2-thiones. The latter species can be also obtained by using the eco compatible TPPH4Cl2 catalyst, which is able to simultaneously activate CS2 and aziridine molecules. The comparison of the overall energy gains of the reaction between aziridines and CS2 with respect to the same process involving CO2, revealed that the formation of thiazolidine-2-thiones is more favoured than the synthesis of oxazolidin-2-ones paving the way to develop efficient and eco-compatible synthesis of thiazolidine-2-thiones.

In this work the mechanism of L-lactide polymerization promoted by NSSN zirconium complexes was investigated through DFT methods with the aim to understand as the electronic and steric features of the ligand affect the energy reaction. It was observed that the rate determining step of the process is the opening of the L-lactide ring and that by increasing the steric hindrance, evaluated by changing geometric parameters and topographic steric maps, or the electron-withdrawing properties of the ligand, the corresponding energy barrier increases. On the other hand, calculations foresee that a small and electron-releasing substituent on the nitrogen atom of the ligand, such as the methyl group, is desirable in order to obtain NSSN zirconium based catalysts with improved activity in the ROP of the L-lactide.

The protonation of commercially available porphyrin ligands yields a class of bifunctional catalysts able to promote the synthesis of N-alkyl oxazolidinones by the CO2cycloaddition to corresponding aziridines. The catalytic system does not require the presence of any Lewis baseor additive and shows interesting features both in terms of cost-effectiveness and eco-compatibility. The metal-freemethodology is active by using the low catalytic loading of 1% mol and the chemical stability of the protonated porphyrin allowed its recycle for three consecutive times without any decrease of performances. In addition, a DFT study was performed in orderto suggest how a simple protonated porphyrin can mediate the CO2cycloaddition to aziridines yielding oxazolidinones.

The direct chemical vapor deposition (CVD) of graphene on industrially preferred semiconductor (like Si wafers) or dielectric substrates has been considered a valid alternative to directly incorporate graphene into electronic devices, thus preventing the common transfer process of the as-grown film which inevitably induce residual contamination and mechanical defects.1 Usually, the thermal CVD synthesis of graphene on Si substrates is realized with methane at high temperature (>900°C), although the low diffusivity of carbon species and the strong carbon solubility on Si which induce unavoidable formation of SiC buffer layers severely hamper an efficient growth.2 Though several strategies have been adopted to overcome such limitations, few studies are focused on aromatic hydrocarbons as possible carbon precursors. 3 In this work, we investigate at the molecular-level the first decomposition steps of toluene and possible recombi- nation pathways of as-formed active species onto the reconstructed Si(100)-c(4x2) surface through density functional theory (DFT) calculations with van der Waals corrections (DFT-D3). First, toluene molecules can chemisorb with sev- eral configurations onto the Si surface by addition reactions.4 We found the most stable configuration (the aromatic ring forming four sigma bonds with two adjacent Si dimers) with adsorption energy of -1.39 eV which is higher than the value reported in,4 mainly due to the inclusion of the DFT-D3 corrections in this work. Then, the minimum energy pathway (MEP) and transition state (TS) of chemical reactions (decomposition and recombination steps) were investi- gated through the climbing-image nudged elastic band (CI-NEB) method. The dehydrogenation of the methyl group of toluene were found the most likely early decomposition path with an energy barrier of 1.4 eV. However, the formation of CH3 radicals is strongly hampered by the much higher energy required for demethylation. Finally, we investigated the formation of anthracene (three connected phenyl rings) as one of the possible stable graphene nuclei for which we found a strong adsorption energy of -2.43 eV. Such carbon structure was achieved by a recombination of two C7H5 radicals and described by a two-step reaction, as shown in Fig.1. However, the cost to produce anthracene through this pathway is rather high with an energy barrier of at least 2.6 eV which is not beneficial for the low-temperature CVD synthesis of graphene on Si(100). References 1 H. Wang, G. Yu, Direct cvd graphene growth on semiconductors and dielectrics for transfer-free device fabrication, Advanced Materials 28 (25) (2016) 4956-4975. 2 A. Khan, M. R. Habib, C. Jingkun, M. Xu, D. Yang, X. Yu, New insight into the metal-catalyst-free direct chemical vapor deposition growth of graphene on silicon substrates, The Journal of Physical Chemistry C 125 (3) (2021) 1774-1783. 3 Tau O., Prete P., Lovergine N., Submitted to Carbon, 2022. 4 F. Costanzo, C. Sbraccia, P. L. Silvestrelli, F. Ancilotto, Theoretical study of toluene chemisorption on si (100), The Journal of Physical Chemistry B 107 (37) (2003) 10209-10215.

The synthesis of a supramolecular hybrid perchlorate salt using the aromatic amine 2,6-diaminopyridine afforded an unexpected crystal structure with non centrosymmetric crystallographic symmetry. The synthesized material with formula (C 5 H 8 N 3 )ClO 4 crystallize according to the monoclinic symmetry in the space group P 2 1 . The observed supramolecular crystal structure, consisting of only weak interactions in all the three dimensions, built from hydrogen bonds and through Anion...pi+ interaction between (ClO 4 ) - tetrahedrons of the mineral part and the aromatic rings of the organic molecules, is rarely observed for similar compounds. The electronic and optical properties are characterized at the theoretical level using DFT; these characterizations demonstrate a moderate direct band gap and a high optical anisotropy. Our results provide the essential information about structural, electronic and optical properties of (C 5 H 8 N 3 )ClO 4 , which are useful for guiding the future studies. (c) 2022 Elsevier B.V. All rights reserved.

Two ethoxy containing ionic liquids (ILs) sharing the same anion, N-trimethyl-N (2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (N111(2O1)-TFSI) and N,N-diethyl-N-methyl-N (2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (N122(2O1)-TFSI), and their mixtures are studied by means of differential scanning calorimetry and infrared spectroscopy combined with DFT calculations. The two ILs, slightly differing only for the length of two short chains, diverge significantly in the thermal properties: N111(2O1)-TFSI undergoes to a crystallization upon cooling, whereas N122(2O1)-TFSI is likely to become a glass. Experimental results indicate that in N111(2O1)-TFSI the occurrence of hydrogen bonding is energetically favored, and become particularly evident in the solid phase. The comparison with computational results indicates that it could be ascribed to the CH bonds involving the C atoms directly linked to the central N atom. In N122(2O1)-TFSI, DFT calculations suggest that hydrogen bonding could take place; however, IR measurements suggest that hydrogen bonding is not energetically favored. Moreover, in N122(2O1)-TFSI there is a larger conformational disorder that prevents from the alignment of cation and anion that contributes to the detection of clear hydrogen bonding infrared active bands. The mixtures rich in N111(2O1)-TFSI crystallize at lower temperatures than the pure ionic liquid. Progressively, the energy gain due to the instauration of hydrogen bonding decreases as the concentration of N122(2O1)-TFSI increases.

A combined experimental and theoretical study shows how the interaction of VUV radiation with cyclo-(alanine-alanine), one of the 2,5-diketopiperazines (DKPs), produces reactive oxazolidinone intermediates. The theoretical simulations reveal that the interaction of these intermediates with other neutral and charged fragments, released in the molecular decomposition, leads either to the reconstruction of the cyclic dipeptide or to the formation of longer linear peptide chains. These results may explain how DKPs could have, on one hand, survived hostile chemical environments and, on the other, provided the seed for amino acid polymerization. Shedding light on the mechanisms of production of such prebiotic building blocks is of paramount importance to understanding the abiotic synthesis of relevant biologically active compounds.

The concept of orthogonality between halogen and hydrogen bonding, brought out by Ho and coworkers some years ago, has become a widely accepted idea within the chemists' community. While the original work was based on a common carbonyl oxygen as acceptor for both interactions, we explore here, by means of M06-2X, M11, omega B97X, and omega B97XD/aug-cc-PVTZ DFT calculations, the interdependence of halogen and hydrogen bonding with a shared pi-electron system of benzene. The donor groups (specifically NCBr and H2O) were placed on either or the same side of the ring, according to a double T-shaped or a perpendicular geometry, respectively. The results demonstrate that the two interactions with benzene are not strictly independent on each other, therefore outlining that the orthogonality between halogen and hydrogen bonding, intended as energetical independence between the two interactions, should be carefully evaluated according to the specific acceptor group.

Metal complexes incorporating proton-responsive ligands have been proved to be superior catalysts in reactions involving the H2 molecule. In this contribution, a series of IrIII complexes based on lutidine-derived CNNH pincers containing N-heterocyclic carbene and secondary amino NHR [R = Ph (4a), tBu (4b), benzyl (4c)] donors as flanking groups have been synthesized and tested in the dehydrogenation of ammonia-borane (NH3BH3, AB) in the presence of substoichiometric amounts (2.5 equiv) of tBuOK. These preactivated derivatives are efficient catalysts in AB dehydrogenation in THF at room temperature, albeit significantly different reaction rates were observed. Thus, by using 0.4 mol % of 4a, 1.0 equiv of H2 per mole of AB was released in 8.5 min (turnover frequency (TOF50%) = 1875 h-1), while complexes 4b and 4c (0.8 mol %) exhibited lower catalytic activities (TOF50% = 55-60 h-1). 4a is currently the best performing IrIII homogeneous catalyst for AB dehydrogenation. Kinetic rate measurements show a zero-order dependence with respect to AB, and first order with the catalyst in the dehydrogenation with 4a (-d[AB]/dt = k[4a]). Conversely, the reaction with 4b is second order in AB and first order in the catalyst (-d[AB]/dt = k[4b][AB]2). Moreover, the reactions of the derivatives 4a and 4b with an excess of tBuOK (2.5 equiv) have been analyzed through NMR spectroscopy. For the former precursor, formation of the iridate 5 was observed as a result of a double deprotonation at the amine and the NHC pincer arm. In marked contrast, in the case of 4b, a monodeprotonated (at the pincer NHC-arm) species 6 is observed upon reaction with tBuOK. Complex 6 is capable of activating H2 reversibly to yield the trihydride derivative 7. Finally, DFT calculations of the first AB dehydrogenation step catalyzed by 5 has been performed at the DFT//MN15 level of theory in order to get information on the predominant metal-ligand cooperation mode.

The equilibria in the solution of three different oxidovanadium(IV) complexes, VO(dhp)2 (dhp = 1,2-dimethyl-3-hydroxy-4(1H)-pyridinonato), VO(ma)2 (ma = maltolato) and VO(pic)2(H2O) (pic = picolinato), were examined in the temperature range of 120-352 K through a combination of instrumental (EPR spectroscopy) and computational techniques (DFT methods). The results revealed that a general equilibrium exists: VOL2 + H2O ? cis-VOL2(H2O) ? trans-VOL2(H2O), where cis and trans refer to the relative position of H2O and the oxido ligand. The equilibrium is more or less shifted to the right depending on the ligand, the temperature, the ionic strength and the coordinating properties of the solvent. With VO(dhp)2, only the square pyramidal species exists at 298 K in aqueous solution, while at 120 K the cis- and trans-VO(dhp)2(H2O) species are also present. The complex of maltol exists almost exclusively in the form cis-VO(ma)2(H2O) in aqueous solution at 298 K, while the trans species can be revealed only at higher temperatures, where the EPR linewidth significantly decreases. The equilibria involving 1-methylimidazole (MeIm), a model for the side chain His coordination, are also influenced by temperature, with its coordination being favored by decreasing the temperature. The implications of these results in the study of the (vanadium complex)-protein systems are discussed and the interaction with myoglobin (Mb) is examined as a representative example.

The good chelating properties of hydroxypyrone (HPO) derivatives towards oxidovanadium(IV) cation, VO, constitute the precondition for the development of new insulinmimetic and anticancer compounds. In the present work, we examined the VO complex formation equilibria of two kojic acid (KA) derivatives, L4 and L9, structurally constituted by two kojic acid units linked in position 6 through methylene diamine and diethyl-ethylenediamine, respectively. These chemical systems have been characterized in solution by the combined use of various complementary techniques, as UV-vis spectrophotometry, potentiometry, NMR and EPR spectroscopy, ESI-MS spectrometry, and DFT calculations. The thermodynamic approach allowed proposing a chemical coordination model and the calculation of the complex formation constants. Both ligands L4 and L9 form 1:1 binuclear complexes at acidic and physiological pHs, with various protonation degrees in which two KA units coordinate each VO ion. The joined use of different techniques allowed reaching a coherent vision of the complexation models of the two ligands toward oxidovanadium(IV) ion in aqueous solution. The high stability of the formed species and the binuclear structure may favor their biological action, and represent a good starting point toward the design of new pharmacologically active vanadium species.

Succinic acid is an important intermediate for the production of commodity chemicals and the world market potential of its derivatives is estimated to be around 270.000 t/year. Above all, succinates find applications in various industrial fields, such as cosmetics, agricultural chemistry, food industry and material science. In this context, based on our knowledge on the carbonylation reactions of unsaturated substrates, we have recently developed an efficient, low-cost and one-pot methodology for the synthesis of succinic acid derivatives. In particular, we were able to carry out the bis-alkoxycarbonylation of olefins using palladium/aryl ?-diimine complexes as catalysts, obtaining succinates in high yields and selectivities, under mild reaction conditions. The reaction proceeds utilizing p-benzoquinone as oxidant and p-TSA as additive, in the presence of an alcohol, which acts both as a solvent and as nucleophile, under 4 bar of carbon monoxide at 20°C. The most active catalysts are easily formed in situ by mixing Pd(TFA)2 and the nitrogen ligands 1a or 1b, in THF. This process has also been successfully applied to particularly low-reactive olefins, such as 1,2-disubstituted olefins,[3] including unsaturated fatty acid methyl esters, or acrylic esters and acrylic amides. Interestingly, when internal olefins are utilized, the process turned out to be diastereospecific and no Pd-catalyzed isomerization of the double bond has been observed. Our studies, in addition to providing a complete library of succinates, allowed us to highlight some relevant aspects of the catalytic cycle of the bis-alkoxycarbonylation reaction, through mechanistic investigations carried out with ab-initio calculations. Here, our latest results on the bis-alkoxycarbonylation process will be presented.

Cyclic trinuclear complexes (CTCs) of d10 metal frames, obtained through the reaction between angular ditopic anionic bridging ligands and 11th group elements M(I) complexes, have aroused considerable attention due to their potential application in optoelectronics and molecular recognition. Experimental evidences show that the reaction of gold(I) CTCs, featuring imidazolate bridging ligands, with different substrates (CH3I and I2) result to the formation of carbene, bis-carbene or square planar complexes depending on the nature of both the reactants depending on and of the substituent at the imidazolyl ring. Herein, we report the results of a detailed computational investigation of the reactivity by considering two different substituents at the ring ligand: methyl or benzyl groups. All the electronic and steric factors ruling the reactivity have been pointed out and, in particular, the not innocent behaviour of the imidazolyl rings in the activation of C-I bonding. Experimentally, the X-ray crystal structure demonstrates that the reaction between the gold(I) CTC - having 1-methyl-imidazolate as bridging ligand- with MeI provides the formation of a square planar gold complex with the formation of new Au-I and Au-CH3 linkages. In Figure 1 is reported the optimized structure obtained by computational calculations within Gaussian 16 package. Such a reactivity, beyond to the classic addition of iodine traditionally classified as "oxidative addition", has been explained accordingly to the newly introduced Inverted Ligand Field concept. A reasonable explanation has been also provided for the role of the different substituents at the imidazolyl ring in the reactivity.

The development of semiconductor polymers for electronic applications requires tailored synthetic strategies to obtain materials with tunable electronic properties and morphology to enhance their properties. Towards this goal, here is reported the expedient synthesis of a novel class of thiophene-based electrochromic polymers, processable in organic solvents and as nanoparticles (NPs) in water. Their characterization and application in flexible solid-state electrochromic devices (ECDs) are described. All polymers have a repeat unit made of the same linear thienyl-phenyl-thienyl-thienyl fragment. The tuning of the electro-optical properties is achieved by introducing alkyl or alkoxy substituents in thiophene and/or by the presence of either -CH-CH- or -CH-CH- linkers connecting the repeat units and acting as conjugation modulators. The ECDs display a bright yellow or red/magenta color in the neutral state and dark blue in the oxidized state. Redox potentials, color contrast, switching time, and stability of the devices are reported, and it is demonstrated that the use of NPs films spray-coated from water instead of cast films from chloroform significantly improves their performance. Density functional theory calculations allow to elucidate the relationship between polymer structure and electrochromic properties and shed light on electronic structure changes upon oxidation, in agreement with spectroelectrochemistry.