From Small Metal Clusters to Molecular Nanoarchitectures with a Core-Shell Structure: The Synthesis, Redox Fingerprint, Theoretical Analysis, and Solid-State Structure of [Co38As12(CO)50]4.

The cluster [Co38As12(CO)50]4- was obtained by pyrolysis of [Co6As(CO)16]-. The metal cage features a closed-packed core inside a Co/As shell that progressively deforms from a cubic face-centered symmetry. The redox and acid-base reactivities were determined by cyclic voltammetry and spectrophotometric titrations. The calculated electron density revealed the shell-constrained distribution of the atomic charges, induced by the presence of arsenic.

Different Metallophilic Attitudes Revealed by Compression.

Two isostructural coordination polymers with coinage metal(I) cations were compressed with the purpose of testing interactions between chains, which may trigger metallophilic interactions or otherwise expand the metal coordination. DFT calculations and X-ray diffraction studies reveal an extraordinary difference between Ag(I) and Cu(I) in homologous compounds. Argentophilic interactions are favored by a mild compression, and at P = 7.94 GPa, the Ag-Ag distance matches the value of metallic silver. On the other hand, no cuprophilic interaction is activated even by compression up to 8 GPa, and Cu-Cu distances remain outside the van der Waals spheres.

On generalized partition methods for interaction energies.

The breakdown of interaction energy has always been a very important means to understand chemical bonding and it has become a seamlessly useful tool for modern supramolecular chemistry. Many interaction schemes and partitioning methods are known and widely adopted. Their common mechanism is the fragmentation of a chemical system into smaller moieties and the identification of interaction energy contributions somewhat related to a physical phenomenon. However, the definitions of energy terms and of the molecular fragments are not universal, leading to complicated comparisons among different approaches and controversial interpretations. The most adopted methodologies use a partition of the Hilbert space or of the position space. In this paper, we propose a protocol to compare energy decomposition methods based on two schemes representative of each category, namely the energy decomposition analysis (EDA, Hilbert space) and the interacting quantum atom (IQA, position space).

Experimental and theoretical electron density of intermediates in palladium-phenanthroline catalyzed carbonylation of amines and reductive carbonylation of nitroarenes.

The accurate electron density distribution in Pd(Neoc)Cl2 (CO) (Neoc = 2,9-dimethyl-1,10-phenanthroline) was measured and calculated to investigate the chemical bonding features, the electrostatic forces and the polarizable bonds in this complex, which is a prototype of the proposed intermediate in the catalytic carbonylation of amines and nitroarenes. The quantum theory of atoms in molecules enables to investigate the nature of the elusive fifth coordination in the complex, which is approximately intermediate between a bypiramid penta-coordination and a square planar tetra-coordination. The analysis of the electrostatic potential and of the distributed atomic polarizabilities enables to address the sites that are more prompt to react, in particular in the context of the catalytic cycle. © 2017 Wiley Periodicals, Inc.

Sol-gel TiO2 colloidal suspensions and nanostructured thin films: structural and biological assessments.

The role of substrate topography in phenotype expression of in vitro cultured cells has been widely assessed. However, the production of the nanostructured interface via the deposition of sol-gel synthesized nanoparticles (NPs) has not yet been fully exploited. This is also evidenced by the limited number of studies correlating the morphological, structural and chemical properties of the grown thin films with those of the sol-gel 'brick' within the framework of the bottom-up approach. Our work intends to go beyond this drawback presenting an accurate investigation of sol-gel TiO2 NPs shaped as spheres and rods. They have been fully characterized by complementary analytical techniques both suspended in apolar solvents, by dynamic light scattering (DLS) and nuclear magnetic resonance (NMR) and after deposition on substrates (solid state configuration) by transmission electron microscopy (TEM) and powder x-ray diffraction (PXRD). In the case of suspended anisotropic rods, the experimental DLS data, analyzed by the Tirado-Garcia de la Torre model, present the following ranges of dimensions: 4-5 nm diameter (∅) and 11-15 nm length (L). These results are in good agreement with that obtained by the two solid state techniques, namely 3.8(9) nm ∅ and 13.8(2.5) nm L from TEM and 5.6(1) ∅ and 13.3(1) nm L from PXRD data. To prove the suitability of the supported sol-gel NPs for biological issues, spheres and rods have been separately deposited on coverslips. The cell response has been ascertained by evaluating the adhesion of the epithelial cell line Madin-Darby canine kidney. The cellular analysis showed that titania films promote cell adhesion as well clustering organization, which is a distinguishing feature of this type of cell line. Thus, the use of nanostructured substrates via sol-gel could be considered a good candidate for cell culture with the further advantages of likely scalability and interfaceability with many different materials usable as supports.

An interacting quantum atoms analysis of the metal-metal bond in [M2(CO)8]n systems.

The metal-metal interaction in policarbonyl metal clusters remains one of the most challenging and controversial issues in metal-organic chemistry, being at heart of a generalized understanding of chemical bonding and of specific applications of these molecules. In this work, the interacting quantum atoms (IQA) approach is used to study the metal-metal interaction in dimetal polycarbonyl dimers, analyzing bridged (Co2(CO)8)), semibridged ([FeCo(CO)8](-)) and unbridged (Co2(CO)8, [Fe2(CO)8](2-)) clusters. In all systems, a delocalized covalent bond is found to occur, involving the metals and the carbonyls, but the global stability of the dimers mainly originates from the Coulombic attraction between the metals and the oxygens.

Probing hydrogen bond networks in half-sandwich Ru(II) building blocks by a combined 1H DQ CRAMPS solid-state NMR, XRPD, and DFT approach.

The hydrogen bond network of three polymorphs (1α, 1ß, and 1γ) and one solvate form (1·H2O) arising from the hydration-dehydration process of the Ru(II) complex [(p-cymene)Ru(κN-INA)Cl2] (where INA is isonicotinic acid), has been ascertained by means of one-dimensional (1D) and two-dimensional (2D) double quantum (1)H CRAMPS (Combined Rotation and Multiple Pulses Sequences) and (13)C CPMAS solid-state NMR experiments. The resolution improvement provided by homonuclear decoupling pulse sequences, with respect to fast MAS experiments, has been highlighted. The solid-state structure of 1γ has been fully characterized by combining X-ray powder diffraction (XRPD), solid-state NMR, and periodic plane-wave first-principles calculations. None of the forms show the expected supramolecular cyclic dimerization of the carboxylic functions of INA, because of the presence of Cl atoms as strong hydrogen bond (HB) acceptors. The hydration-dehydration process of the complex has been discussed in terms of structure and HB rearrangements.

CO2 Adsorption in a Robust Iron(III) Pyrazolate-Based MOF: Molecular-Level Details and Frameworks Dynamics From Powder X-ray Diffraction Adsorption Isotherms.

Understanding adsorption processes at the molecular level, with multi-technique approaches, is nowadays at the frontier of porous materials research. In this work it is shown that with a proper data treatment, in situ high-resolution powder X-ray diffraction (HR-PXRD) at variable temperature and gas pressure can reveal atomic details of the accommodation sites, the framework dynamics as well as thermodynamic information (isosteric heat of adsorption) of the CO2 adsorption process in the robust iron(III) pyrazolate-based MOF Fe2(BDP)3 [H2BDP = 1,4-bis(1H-pyrazol-4-yl)benzene]. Highly reliable "HR-PXRD adsorption isotherms" can be constructed from occupancy values of CO2 molecules. The "HR-PXRD adsorption isotherms" accurately match the results of conventional static and dynamic gas sorption experiments and Monte Carlo simulations. These results are indicative of the impact of the molecular-level behavior on the bulk properties of the system under study and of the potential of the presented multi-technique approach to understand adsorption processes in metal-organic frameworks.

Switching of emissive and NLO properties in push-pull chromophores with crescent PPV-like structures.

We report on a series of novel homologous push-pull compounds, in which identical donor (a dimethylamino) and acceptor (a malonate ester) functionalities endcap crescent PPV fragments, bearing, respectively, 1, 2 and 3 p-phenylenevinylene units in direct linear conjugation (compounds 7-9). The three compounds exhibit striking differences in their linear and nonlinear optical properties. The shorter compound 7 exhibits aggregation-induced emission with a strong luminescence in the solid state (blue emission, photoluminescence quantum yield 38%), and it is nonemissive in solution; the more extended conjugated systems 8 and 9 show classical aggregation-caused quenching in the solid state, while high quantum yield photoluminescence (21 and 93% in toluene) is restored in diluted solutions, through mechanisms involving intramolecular charge transfer in the excited states. EFISH measurements in solutions demonstrate a strong solvent and concentration dependence. As rationalized with the aid of molecular modelling, compounds 8 and, more markedly, 9 aggregate in stable centrosymmetric dimers in solution.

Synthesis, reactivity, electrochemical behavior, and crystal structure of a family of multivalent metal carbido-carbonyl clusters based on the Rh10(C)2Au(4-6) framework.

Six metal carbido-carbonyl clusters have been isolated and recognized as members of a multivalent family based on the dioctahedral Rh(10)(C)(2) frame, with variable numbers of CO ligands, AuPPh(3) moieties, and anionic charge: [Rh(10)(C)(2)(CO)(x)(AuPPh(3))(y)](n-) (x = 18, 20; y = 4, 5, 6; n = 0, 1, 2). Anions [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)](-) ([2](-)) and [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)](2-) ([2](2-)) have been obtained by the reduction of [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)] (2) under N(2), while [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(5)](-) ([3](-)) was obtained from [Rh(10)(C)(2)(CO)(20)(AuPPh(3))(4)] (1) by reduction under a CO atmosphere. [3](-) can be better obtained by the addition of AuPPh(3)Cl to [2](2-). [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(6)] (4) is obtained from [3](-) and 2 as well by the reduction and subsequent addition of AuPPh(3)Cl. The molecular structures of [2](2-) ([NBu(4)](+) salt), [3](-) ([NMe(4)](+) salt), and 4 have been determined by single-crystal X-ray diffraction. The redox activities of complexes 1, 2 and [3](-) have been investigated by electrochemical and electron paramagnetic resonance (EPR) techniques. The data from EPR spectroscopy have been accounted for by theoretical calculations.

Restoring orbital thinking from real space descriptions: bonding in classical and non-classical transition metal carbonyls.

A combined strategy that unifies our interacting quantum atoms approach (IQA), a chemically intuitive energetic perspective within the quantum theory of atoms in molecules (QTAIM), the domain natural orbitals obtained by the diagonalization of the charge-weighted domain-averaged Fermi hole (DAFH), and the statistical analyses of chemical bonding provided by the electron number distribution functions (EDF) is presented. As shown, it allows for recovering traditional orbital images from the orbital invariant descriptions of QTAIM. It does also provide bonding indices (like bond orders) and bond energetics, all in a per orbital basis, still invariant manner, using a single unified framework. The procedure is applied to show how the Dewar, Chatt, and Ducanson model of bonding in simple transition metal carbonyls may be recovered in the real space. The balance between the number of σ-donated and π-backdonated electrons is negative in classical compounds and positive in non-classical ones. The energetic strength of backdonation is, however, smaller than that of donation. Our technique surpasses conventional orbital models by providing physically sound, quantitative energetics of chemical bonds (or interactions) together with effective one-electron pictures, all for arbitrary wavefunctions.

Efficient crystallization induced emissive materials based on a simple push-pull molecular structure.

Solid state luminescent materials are the subject of ever growing interest both from a scientific and a technological point of view. Aggregation caused quenching (ACQ) processes however represent an obstacle to the development of most luminogens in the condensed phase. This is why particularly fascinating are those materials showing higher emission intensity in the solid state than in solution. Here we report on three 4-dialkylamino-2-benzylidene malonic acid dialkyl esters, very simple push-pull molecules, which are hardly emissive in solution and in the amorphous phase but become good emitters in the crystalline phase according to what has been indicated as crystallization induced emission (CIE). Thanks to combined emission and NMR spectroscopies at different temperatures on the prototype compound 4-dimethylamino-2-benzylidene malonic acid dimethyl ester in solution, we give full evidence that a restricted intramolecular rotation (RIR) phenomenon, in particular the hindered rotation around the aryl main axis of the compound, is at the origin of this behaviour. In addition, solid state photophysical and X-ray diffraction structural characterization allow us to identify J-dimeric interactions as responsible for the particularly intense emission of two of the three compounds. Moreover, by exploiting the compounds' acidochromic properties, applications in sensors and optoelectronics are envisaged.

Highly emitting concomitant polymorphic crystals of a dinuclear rhenium complex.

The dinuclear complex [Re(2)(µ-Cl)(2)(CO)(6)(µ-4,5-(Me(3)Si)(2)pyridazine)] gives in the solid state two polymorphs (yellow, 1Y, and orange, 1O), which can be either concomitantly or separately obtained on varying the crystallization rate. Both crystal phases exhibit intense photoluminescence from the lowest lying triplet metal-to-ligand charge transfer state, much stronger than in solution (quantum yields 0.56 and 0.52, for 1O and 1Y respectively, vs 0.06 in toluene), likely due to the restricted rotation of the Me(3)Si groups in the solid state. A clean, irreversible 1O → 1Y single-crystal-to-single-crystal phase transition occurs at 443 K, as revealed by variable temperature X-ray diffraction analysis. In spite of the absence of any strong intermolecular interactions in both forms, 1O and 1Y show very different absorption and emission maxima (λ(abs) 370 and 393 nm, λ(em) 534 and 570 nm, for 1Y and 1O, respectively). This behavior highlights the importance of the local organization of molecular dipoles in perturbing the photophysical properties of the molecule in the crystal.

Slow relaxation of the magnetization in non-linear optical active layered mixed metal oxalate chains.

New Co(II) members of the family of multifunctional materials of general formula [DAMS](4)[M(2)Co(C(2)O(4))(6)]·2DAMBA·2H(2)O (M(III) = Rh, Fe, Cr; DAMBA = para-dimethylaminobenzaldehyde and [DAMS(+)] = trans-4-(4-dimethylaminostyryl)-1-methylpyridinium) have been isolated and characterized. Such new hybrid mixed metal oxalates are isostructural with the previously investigated containing Zn(II), Mn(II), and Ni(II). This allows to preserve the exceptional second harmonic generation (SHG) activity, due to both the large molecular quadratic hyperpolarizability of [DAMS(+)] and the efficiency of the crystalline network which organizes [DAMS(+)] into head-to-tail arranged J-type aggregates, and to further tune the magnetic properties. In particular, the magnetic data of the Rh(III) derivative demonstrate that high spin octacoordinated Co(II) centers behave very similarly to the hexacoordinated Co(II) ones, being dominated by a large orbital contribution. The Cr(III) derivative is characterized by ferromagnetic Cr(III)-Co(II) interactions. Most relevantly, the Fe(III) compound is characterized by a moderate antiferromagnetic interaction between Fe(III) and Co(II), resulting in a ferrimagnetic like structure. Its low temperature dynamic magnetic properties were found to follow a thermally activated behavior (τ(0) = 8.6 × 10(-11) s and ΔE = 21.4 K) and make this a candidate for the second oxalate-based single chain magnet (SCM) reported up to date, a property which in this case is coupled to the second order non linear optical (NLO) ones.

Molecular crystals under high pressure: theoretical and experimental investigations of the solid-solid phase transitions in [Co2(CO)6(XPh3)2] (X = P, As).

An accurate analysis of the solid-state structural transformations occurring in species of the general formula [Co(2)(CO)(6)(XPh(3))(2)] (X = P, As) by experimental X-ray diffraction under non-ambient conditions (on variation of pressure or temperature) and by ab initio theoretical modelling is presented. After a crystal-to-crystal phase transition, the conformation of carbonyl ligands about the Co-Co bond changes from staggered to (almost) eclipsed. The analysis of high-pressure and low-temperature structures sheds light on the peculiar behaviour of the metal-metal bond, the most flexible in the molecule, which is initially compressed, then elongated due to increased intra-carbonyl repulsion and eventually compressed again. Theoretical calculations in the solid state allow the thermodynamic quantities of the transformation to be computed and prediction of the distortions produced by the external stress. The change in molecular symmetry is induced by the increase in the high internal energy associated with the staggered carbonyl conformation, which does not allow efficient packing if the crystalline volume is reduced. The eclipsed conformer, though much less stable in isolation, guarantees better entanglement between molecules.

Hydrogen migration in oxalic acid di-hydrate at high pressure?

Single crystal X-ray diffraction of oxalic acid dihydrate H(2)C(2)O(4).2H(2)O (1), at pressures up to 5.3 GPa, shows significant changes in the molecular geometries, probably accompanied by a proton migration from H(2)C(2)O(4) to H(2)O and formation of ionic species, as predicted by periodic DFT calculations.

Structures from powders: polynuclear Hg(II) complexes containing the flexible bisimidazolylmethane ligand.

Several polynuclear Hg(II) complexes containing the flexible ditopic bisimidazolylmethane ligand (C(7)H(8)N(4), bim) have been prepared by reaction of equimolar quantities of mercury salts (acetate, cyanide, thiocyanate, chloride, and iodide) in EtOH or acetonitrile solution. Their crystal and molecular structures were retrieved from laboratory powder diffraction data, and their thermal properties were fully characterized, including the determination of the thermal expansion coefficients and the related strain tensor using thermodiffractometric methods. [Hg(bim)(CH(3)COO)(2)](2) consists of cyclic dimers with chelating acetates, while the [Hg(bim)X(2)](n) species (X = Cl, CN, SCN, and I) are one-dimensional polymers, with dangling X groups. A further complex of nominal Hg(2)(bim)Cl(2) formulation was also prepared, but the complexity and nonideality of its powder diffraction traces prevented the determination of its main structural features.

Thermally induced interconversions of metal-pyrimidine-4,6-dicarboxylate polymers: a structural, spectroscopic, and magnetic study.

Continuing our work on the structural and magnetic aspects of the one-dimensional (1-D) coordination polymers of the [M(pmdc)(H(2)O)(2)] x H(2)O kind (M = Fe, Co, Ni, Cu, Zn; pmdc = pyrimidine-4,6-dicarboxylate), we have combined ab initio X-ray powder diffraction methods with in situ thermodiffractometry and thermal analyses to characterize the selective and reversible transformation of the [M(pmdc)(H(2)O)(2)] x H(2)O compounds (M = Fe, Co, Ni, Cu) into the bis-hydrated [M(pmdc)(H(2)O)(2)] counterparts by moderate heating, which is followed by an irreversible transformation into two-dimensional (2-D) anhydrous species. The structural features of the transient bis-hydrated species and of the completely dehydrated one are described for M = Cu. Remarkably, the first dehydration process does not alter the 1-D nature of the [M(pmdc)(H(2)O)(2)] chains; on the contrary, the second dehydration gives rise to the loss of the axially coordinated water molecules with a concomitant condensation of the 1-D chains into 2-D layers through ancillary carboxylate bridging groups. The magnetic properties of the anhydrous [M(pmdc)] species (M = Co, Ni, Cu) have been investigated, showing that these phases behave as 1-D antiferromagnets with interchain interactions. Notably, in the case of the [Ni(pmdc)] system, a weak ferromagnetic ordering, arising from a spin canting phenomenon with a blocking temperature of 13 K, is observed.

Crystal structure of pirfenidone (5-methyl-1-phenyl-1H-pyridin-2-one): an active pharmaceutical ingredient (API).

The crystal structure of pirfenidone, C12H11NO [alternative name: 5-methyl-1-phenyl-pyridin-2(1H)-one], an active pharmaceutical ingredient (API) approved in Europe and Japan for the treatment of Idiopathic pulmonary fibrosis (IPF), is reported here for the first time. It was crystallized from toluene by the temperature gradient technique, and crystallizes in the chiral monoclinic space group P21. The phenyl and pyridone rings are inclined to each other by 50.30 (11)°. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds involving the same acceptor atom, forming undulating layers lying parallel to the ab plane.

Guest-induced modification of a magnetically active ultramicroporous, gismondine-like, copper(II) coordination network.

A novel ultramicroporous coordination polymer, namely [Cu(F-pymo)2(H2O)1.25]n (1, F-pymo = 5-fluoropyrimidin-2-olate), has been prepared and structurally characterized. 1 displays a zeolitic gismondine (GIS) topology, with ca. 2.9 A wide helical channels which, in the thermally activated counterpart (1'), account for a 13% void volume and are responsible for the observed selective solid-gas adsorption properties toward H2, N2, and CO2. At 77 K 1' behaves as a molecular sieve, selectively adsorbing H2 over N2, possibly due to size-exclusion reasons. At variance, although CO2 molecules are slightly larger than the pore size, they are readily incorporated by 1' at temperatures as high as 433 K. Variable-temperature X-ray powder diffraction (TXRPD) studies, in the temperature range 303-473 K, show that dehydration is reversible and has almost negligible effects on the network. At variance, the uptake of CO2 occurs through a transient phase and channels expansion. While the gas storage capacity of 1' is not very high-H2, 0.56 wt % and 0.010 kg H2/L at 90 K and 900 Torr, and CO2, 7.6 wt % at 273 K and 900 Torr-the guest molecules achieve very high densities, comparable to that of the liquid for H2 (0.023 vs 0.021 molecules A-3) and to that of the solid for CO2 (0.014 vs 0.022 molecules A-3). In addition, we have also studied the effect of the perturbation exerted by the guest molecules on its magnetic properties. The results show that while dehydration of 1 has negligible effect on its spin-canted antiferromagnetic behavior, CO2 incorporation in the pores is responsible for an increment of the transition temperature at which the weak ferromagnetic ordering takes place from 22 to 29 K.