Impact of POM's coordination mode and Mo-hybrid constituents on the binding, stability, and catalytic properties of hybrid (pre)catalysts.

The assembly of MoVIO2 2+ and methoxy-substituted salicylaldehyde nicotinoyl hydrazone ligands afforded two classes of hybrid polyoxometalates (POMs). In the Class I architectures, [MoO2(HL1-3)(D)]2[Mo6O19]·xCH3COCH3 (D = CH3COCH3 or H2O, x = 0 or 2, and L1-3 = ligands bearing the OMe group at position 3, 4 and 5, respectively), the main driving force for self-assembly is the electrostatic interaction between the components. Class II architectures are composed of a POM anion covalently linked to two Mo-complex units through the terminal Ot or bridging µ2-OPOM oxygen atoms, as found in Lindqvist-based hybrids [{MoO2(HL1-3)}2Mo6O19]·xCH3CN (x = 0 or 2) and the asymmetrical ß-octamolybdate-based hybrid [{Mo2O4(HL2)(H2L)}{MoO2(HL2)}2Mo8O26]·CH3CN·H2O. Quantum chemical calculations were applied to evaluate the impact of the POM hybrid constituents on the hybrid-type stability, showing that it strongly depends on the ligand substituent position and ancillary ligand nature. Hybrids were tested as catalysts for cyclooctene epoxidation using tert-butyl hydroperoxide (TBHP in water or decane) and with or without the addition of acetonitrile (CH3CN) as an organic solvent. The catalytic results provided by the use of TBHP in decane are the best ones and classify all the prepared catalysts as very active, with the conversion of cyclooctene >90%, and high selectivity towards epoxide, >80%. We also examined the influence of the ligand structure, POM's hybrid type, and coordination mode on the Mo-hybrid activity and selectivity.

Transition Metal-Based Dimeric Metallosurfactants: From Organic-Inorganic Hybrid Structures and Low-Dimensional Magnets to Metallomicelles.

The dimeric (gemini) as well as metallosurfactants exhibit enhanced physicochemical properties compared with conventional surfactants. By uniting the benefits of both, a series of novel dimeric metallosurfactants of the type (12-2-12)[MBr4] (M = Co, Ni, Cu and Zn) was successfully prepared by the reaction of the dimeric surfactant bis(N,N-dimethyl-N-dodecyl)ethylene-1,2-diammonium dibromide, 12-2-12, and the MBr2 salt. Structures and magnetic properties of the materials were studied comprehensively in the solid state, while their micellization was explored in solution. The obtained results unveil that the incorporation and the choice of transition metal more significantly influence surfactants' structures ((12-2-12)2+ cations adopt V-, U-, or trans-conformations) and the magnetic features (metal ions form 1D or 2D magnetic lattice) than their solution properties. However, all synthesized metallosurfactants display improved self-assembly properties compared with the metal-free precursor. The investigated systems represent a fruitful platform for the development of multifunctional materials as they are simple to produce, can be obtained in high yields, and show advanced properties both in solution and in the solid state. Notably, this work unveils a simple approach to the design and synthesis of novel low-dimensional magnetic systems of great potential for future spintronic and optoelectronic devices.

Direct in situ measurement of polymorphic transition temperatures under thermo-mechanochemical conditions.

For the first time, we directly measured the onset and completion temperatures of polymorphic transitions under thermo-mechanochemical conditions by simultaneous in situ synchrotron powder X-ray diffraction and temperature monitoring. We determined the thermo-mechanochemical polymorphic transition temperature in 1-adamantyl-1-diamantyl ether to be 31 °C lower than the transition temperature determined by DSC. Our findings highlight the uniqueness of thermo-mechanochemical conditions, with potential applications in polymorph screening.

Direct thermodynamic characterization of solid-state reactions by isothermal calorimetry.

Despite the growing importance of solid-state reactions, their thermodynamic characterization has largely remained unexplored. This is in part due to the lack of methodology for measuring the heat effects related to reactions between solid reactants. We address here this gap and report on the first direct thermodynamic study of chemical reactions between solid reactants by isothermal calorimetry. Three reaction classes, cationic host-guest complex formation, molecular co-crystallization, and Baeyer-Villiger oxidation were investigated, showcasing the versatility of the devised methodology to provide detailed insight into the enthalpy changes related to various reactions. The reliability of the method was confirmed by correlation with the values obtained via solution calorimetry using Hess's law. The thermodynamic characterization of solid-state reactions described here will enable a deeper understanding of the factors governing solid-state processes.

Relationships between radionuclides, metals, and sediment properties in sediment of a bay exposed to anthropogenic pressure and mixed sediment sources (Kastela Bay, Adriatic Sea, Croatia).

Natural and anthropogenic radionuclides, metals, organic matter, sediment grain size, mineral composition, and sediment sources were studied in marine sediment of Kastela Bay up to a depth of 0.5 m. Deposition of man-modified material into the sea was evidenced in sediment mineral composition. Presence of pyrite and hematite in this sediment may pose an environmental concern. Metals, radionuclides, and organic matter were grouped in three groups: (i) variables under no anthropogenic influence and preferentially associated with carbonates (Ca, Sr); (ii) variables under no or weak anthropogenic influence and preferentially associated with aluminosilicates (Al, K, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Rb, Y, 40K, 232Th); (iii) variables under notable anthropogenic influence and/or natural processes of separation (Cu, Zn, Pb, As, 226Ra, 238U, 137Cs, organic matter). Predominant influencing parameters change with sediment depth for some variables. Anthropogenic influence was the most emphasised for Cu, Zn, and Pb, followed by 137Cs.

Supramolecular intermediates in thermo-mechanochemical direct amidations.

We present a solvent-free thermo-mechanochemical approach for the direct coupling of carboxylic acids and amines, which avoids activators and additives. Detailed analysis of the reactions by ex situ and in situ monitoring methods led to the observation, isolation, and characterisation of multicomponent crystalline intermediates that precede the formation of amides. We applied our methodology for the quantitative synthesis of the active pharmaceutical ingredient moclobemide.

The Role of Crystalline Intermediates in Mechanochemical Cyclorhodation Reactions Elucidated by in-Situ X-ray Powder Diffraction and Computation.

The occurrence of crystalline intermediates in mechanochemical reactions might be more widespread than previously assumed. For example, a recent study involving the acetate-assisted C-H activation of N-Heterocycles with [Cp*RhCl2 ]2 by ball milling revealed the formation of transient cocrystals between the reagents prior to the C-H activation step. However, such crystalline intermediates were only observed through stepwise intervallic ex-situ analysis, and their exact role in the C-H activation process remained unclear. In this study, we monitored the formation of discrete, stoichiometric cocrystals between benzo[h]quinoline and [Cp*RhCl2 ]2 by ball milling using in-situ synchrotron X-ray powder diffraction. This continuous analysis revealed an initial cocrystal that transformed into a second crystalline form. Computational studies showed that differences in noncovalent interactions made the [Cp*RhCl2 ]2 unit in the later-appearing cocrystal more reactive towards NaOAc. This demonstrated the advantage of cocrystal formation before the acetate-assisted metalation-deprotonation step, and how the net cooperative action of weak interactions between the reagents in mechanochemical experiments can lead to stable supramolecular assemblies, which can enhance substrate activation under ball-milling conditions. This could explain the superiority of some mechanochemical reactions, such as acetate-assisted C-H activation, compared to their solution-based counterparts.

Structure-Related Evolution of Magnetic Order in Anisidinium Tetrachlorocuprates(II).

Tetrachlorocuprate(II) hybrids of the three anisidine isomers (ortho-, meta-, and para-, or 2-, 3-, and 4-methoxyaniline, respectively) were prepared and studied in the solid state via X-ray diffraction and magnetization measurements. Depending on the position of the methoxy group of the organic cation, and subsequently, the overall cation geometry, a layered, defective layered, and the structure comprising discrete tetrachlorocuprate(II) units were obtained for the para-, meta-, and ortho-anisidinium hybrids, respectively. In the case of layered and defective layered structures, this affords quasi-2D-layered magnets, demonstrating a complex interplay of strong and weak magnetic interactions that lead to the long-range ferromagnetic (FM) order. In the case of the structure with discrete CuCl42- ions, a peculiar antiferromagnetic (AFM) behavior was revealed. The structural and electronic origins of magnetism are discussed in detail. To supplement it, the method for calculation of dimensionality of the inorganic framework as a function of interaction length was developed. The same was used to discriminate between n-dimensional and "almost" n-dimensional frameworks, to estimate the organic cation geometry limits for layered halometallates, and to provide additional reasoning behind the observed relation between cation geometry and framework dimensionality, as well as their relation to differences in magnetic behavior.

Diamondoid ether clusters in helium nanodroplets.

Diamondoid ethers were introduced into superfluid helium nanodroplets and the resulting clusters were analyzed by time-of-flight mass spectrometry. Clusters of higher abundances (magic number clusters) were identified and the corresponding potential cluster geometries were obtained from GFN2-xTB and DFT computations. We found that the studied diamondoid ethers readily self-assemble in helium nanodroplets and that London dispersion attraction between hydrocarbon subunits acts as a driving force for cluster formation. On the other hand, hydrogen bonding between ether oxygens and trace water molecules fosters the eventual breakdown of the initial supramolecular aggregate.

Structural Insights into Layered Tetrahalocuprates(II) Based on Small Unsaturated and Cyclic Primary Ammonium Cations.

Layered hybrid halometallates represent a promising class of multifunctional materials, yet with many open challenges regarding the interaction between building blocks. In this work, we present a synthetic and analytical methodology for the efficient synthesis and structural analysis of a series of novel tetrahalocuprate(II) hybrids based on small alkylammonium cations. Observed robustness in geometrical motifs provided a platform for crystal structure determination, even from the complex laboratory powder diffraction data. The slight differences in inorganic layer geometry and severe differences in organic bilayer packing are quantified using well-established descriptors for these materials, and dependences of geometric parameters on anion and cation choice are accounted for. Temperature dependence of structural parameters for one of the tetrachlorocuprate hybrids that was chosen as a model unveils a possible geometrical origin of thermochromism in these materials.

Impedance Spectroscopy as a Powerful Tool for Researching Molybdenum-Based Materials with Schiff Base Hydrazones.

Molybdenum coordination complexes are widely applied due to their biological and pharmacological potential, as well as their performance in different catalytic processes. Parent dioxidomolybdenum Schiff base complexes were prepared via the reaction of [MoO2(acac)2] with a hydrazone Schiff-base tetradentate ligand. A new hydrazone-Schiff base (H2L1 and 2) and its corresponding mononuclear and polynuclear dioxidomolybdenum(VI) complex were synthesized and characterized by spectroscopic methods and elemental analyses, and their thermal behavior was investigated by thermogravimetry. The crystal and molecular structures of H2L2 ligands and the complexes [MoO2(L1)(H2O)], [MoO2(L2)(H2O)], [MoO2(L1)(MeOH)]∙MeOH, [MoO2(L1)(EtOH)]∙EtOH, [MoO2(L1)(2-PrOH)]∙2-PrOH, and [MoO2(L1)]n were determined by single-crystal X-ray diffraction. Using the in situ impedance spectroscopy method (IS), the structural transformations of chosen complexes were followed, and their electrical properties were examined in a wide range of temperatures and frequencies.

Ligand-Modulated Nuclearity and Geometry in Nickel(II) Hydrazone Complexes: From Mononuclear Complexes to Acetato- and/or Phenoxido-Bridged Clusters.

The propensity of 4-hydroxybenzhydrazone-related ligands derived from 3-methoxysalicylaldehyde (H2L3OMe), 4-methoxysalicylaldehyde (H2L4OMe), and salicylaldehyde (H2LH) to act as chelating and/or bridging ligands in Ni(II) complexes was investigated. Three clusters of different nuclearities, [Ni3(L3OMe)2(OAc)2(MeOH)2]∙2MeOH∙MeCN (1∙2MeOH∙MeCN), [Ni2(HL4OMe)(L4OMe)(OAc)(MeOH)2]∙4.7MeOH (2∙4.7MeOH), and [Ni4(HLH)2(LH)2(OAc)2]∙4MeOH·0.63H2O·0.5MeCN·HOAc (3∙4MeOH·0.63H2O·0.5MeCN·HOAc), were prepared from Ni(OAc)2∙4H2O and the corresponding ligand in the presence of Et3N. The hydrazones in these acetato- and phenoxido-bridged clusters acted as singly or doubly deprotonated ligands. When pyridine was used, mononuclear complexes with the square-planar geometry seemed to be favoured, as found for complexes [Ni(L3OMe)(py)] (4), [Ni(L4Ome)(py)] (5) and [Ni(LH)(py)] (6). Ligand substituent effects and the stability of square-planar complexes were investigated and quantified by extensive quantum chemical analysis. Obtained results showed that standard Gibbs energies of binding were lower for square-planar than for octahedral complexes. Starting from [MoO2(L)(EtOH)] complexes as precursors and applying the metal-exchange procedure, the mononuclear complexes [Ni(HL3OMe)2]∙MeOH (7∙MeOH) and [Ni(HLH)]∙2MeOH (9∙2MeOH) and hybrid organic-inorganic compound [Ni2(HL4OMe)2(CH3OH)4][Mo4O10(OCH3)6] (10) were achieved. The octahedral complexes [Ni(HL)2] (7-9) can also be obtained by the direct synthesis from Ni(Oac)2∙4H2O and the appropriate ligand under specific reaction conditions. Crystal and molecular structures of 1∙2MeOH∙MeCN, 2∙4.7MeOH, 3∙4MeOH∙0.63H2O∙0.5MeCN∙HOAc, 4, 5, 9∙2MeOH, and 10 were determined by the single-crystal X-ray diffraction method.

Cocrystal Formation Precedes the Mechanochemically Acetate-Assisted C-H Activation with [Cp*RhCl2 ]2.

This work reports the experimentally studied mechanochemical formation of rhodacycles by ball milling pyridine- and quinoline-derived substrates and [Cp*RhCl2 ]2 in the presence of NaOAc. Ex-situ analysis of the mechanochemical reactions using powder X-ray diffraction (PXRD), solid-state UV-vis spectroscopy and ATR-FTIR spectroscopy revealed the formation of unexpected cocrystals between the substrates and the rhodium dimer prior to the C-H activation step. This sequence of events differs from the generally accepted steps in solution in which cleavage of [Cp*RhCl2 ]2 is initiated by acetate ions. Additionally, the mechanochemical approach enabled the synthesis of the six-membered rhodacycle [Cp*Rh(2-benzilpyridine)Cl], a metal complex repeatedly reported as inaccessible in solution. Altogether, the results of this investigation clarify some of the fundamental aspects of mechanochemical cyclometallations.

Magnetoelectric Multiferroicity and Magnetic Anisotropy in Guanidinium Copper(II) Formate Crystal.

Hybrid metal-organic compounds as relatively new and prosperous magnetoelectric multiferroics provide opportunities to improve the polarization, magnetization and magneto-electric coupling at the same time, which usually have some limitations in the common type-I and type-II multiferroics. In this work we investigate the crystal of guanidinium copper (II) formate [C(NH2)3]Cu(HCOO)3 and give novel insights concerning the structure, magnetic, electric and magneto-electric behaviour of this interesting material. Detailed analysis of crystal structure at 100 K is given. Magnetization points to the copper (II) formate spin-chain phase that becomes ordered below 4.6 K into the canted antiferromagnetic (AFM) state, as a result of super-exchange interaction over different formate bridges. The performed ab-initio colinear density functional theory (DFT) calculations confirm the AFM-like ground state as a first approximation and explain the coupling of spin-chains into the AFM ordered lattice. In versatile measurements of magnetization of a crystal, including transverse component besides the longitudinal one, very large anisotropy is found that might originate from canting of the coordination octahedra around copper (II) in cooperation with the canted AFM order. With cooling down in zero fields the generation of spontaneous polarization is observed step-wise below 270 K and 210 K and the effect of magnetic field on its value is observed also in the paramagnetic phase. Measured polarization is somewhat smaller than the DFT value in the c-direction, possibly due to twin domains present in the crystal. The considerable magneto-electric coupling below the magnetic transition temperature is measured with different orientations of the crystal in magnetic field, giving altogether the new light onto the magneto-electric effect in this material.

(3,5-Di-methyl-adamantan-1-yl)ammonium methane-sulfonate (memanti-nium mesylate): synthesis, structure and solid-state properties.

The asymmetric unit of the title compound, C12H22N+·CH3O3S-, consists of three (3,5-di-methyl-adamantan-1-yl)ammonium cations, C12H22N+, and three methane-sulfonate anions, CH3O3S-. In the crystal, the cations and anions associate via N-H⋯O hydrogen bonds into layers, parallel to the (001) plane, which include large supra-molecular hydrogen-bonded rings.

A unique fluoride nanocontainer: porous molecular capsules can accommodate an unusually high number of "rather labile" fluoride anions.

The present work refers to the challenging issue of fluoride anion recognition/binding in water by taking advantage of the unique possibilities offered by the porous molecular nanocontainers of the {Mo132} Keplerate type allowing the study of a variety of new phenomena. Reaction of the highly reactive carbonate-type capsule with aqueous HF results in the release of carbon dioxide and integration of an unprecedentedly large number of fluoride anions--partly as coordinated ligands at both the pentagonal units and the linkers, partly as a disordered water/fluoride assembly inside the cavity. The internal assembly and some of the fluoride ligands are easily released, which provides interesting options for future studies regarding coordination chemistry and catalysis under confined conditions.

Porous capsules with a large number of active sites: nucleation/growth under confined conditions.

This work deals with the generation of large numbers of active sites and with ensuing nucleation/ growth processes on the inside wall of the cavity of porous nanocapsules of the type (pentagon)12(linker)30≡{(Mo(VI))Mo(VI)5}12{Mo(V)2(ligand)}30. A first example refers to sulfur dioxide capture through displacement of acetate ligands, while the grafted sulfite ligands are able to trap {MoO3H}(+) units thereby forming unusual {(O2SO)3MoO3H}(5-) assemblies. A second example relates to the generation of open coordination sites through release of carbon dioxide upon mild acidification of a carbonate-type capsule. When the reaction is performed in the presence of heptamolybdate ions, MoO4(2-) ions enter the cavity where they bind to the inside wall while forming new types of polyoxomolybdate architectures, thereby extending the molybdenum oxide skeleton of the capsule. Parallels can be drawn with Mo-storage proteins and supported MoO3 catalysts, making the results relevant to molybdenum biochemistry and to catalysis.

Supramolecular stabilization of metastable tautomers in solution and the solid state.

This work presents a successful application of a recently reported supramolecular strategy for stabilization of metastable tautomers in cocrystals to monocomponent, non-heterocyclic, tautomeric solids. Quantum-chemical computations and solution studies show that the investigated Schiff base molecule, derived from 3-methoxysalicylaldehyde and 2-amino-3-hydroxypyridine (ap), is far more stable as the enol tautomer. In the solid state, however, in all three obtained polymorphic forms it exists solely as the keto tautomer, in each case stabilized by an unexpected hydrogen-bonding pattern. Computations have shown that hydrogen bonding of the investigated Schiff base with suitable molecules shifts the tautomeric equilibrium to the less stable keto form. The extremes to which supramolecular stabilization can lead are demonstrated by the two polymorphs of molecular complexes of the Schiff base with ap. The molecules of both constituents of molecular complexes are present as metastable tautomers (keto anion and protonated pyridine, respectively), which stabilize each other through a very strong hydrogen bond. All the obtained solid forms proved stable in various solid-state and solvent-mediated methods used to establish their relative thermodynamic stabilities and possible interconversion conditions.

Desmotropy, polymorphism, and solid-state proton transfer: four solid forms of an aromatic o-hydroxy Schiff base.

The Schiff base derived from salicylaldehyde and 2-amino-3-hydroxypyridine affords a diversity of solid forms, two polymorphic pairs of the enol-imino (D1 a and D1 b) and keto-amino (D2 a and D2 b) desmotropes. The isolated phases, identified by IR spectroscopy, X-ray crystallography, and (13)C cross-polarization/magnetic angle spinning (CP/MAS) NMR spectroscopy, display essentially planar molecular conformations characterized by strong intramolecular hydrogen bonds of the O-H⋅⋅⋅N (D1) or N-H⋅⋅⋅O (D2) type. A change in the position of the proton within this O⋅⋅⋅H⋅⋅⋅N system is accompanied by substantially different molecular conformations and, subsequently, by divergent supramolecular architectures. The appearance and interconversion conditions for each of the four phases have been established on the basis of a number of solution and solvent-free experiments, and evaluated against the results of computational studies. Solid phases readily convert into the most stable form (D1 a) upon exposure to methanol vapor, heating, or by mechanical treatment, and these transformations are accompanied by a change in the color of the sample. The course of thermally induced transformations has been monitored in detail by means of temperature-resolved powder X-ray diffraction and infrared spectroscopy. Upon dissolution, all forms equilibrate immediately, as confirmed by NMR and UV/Vis spectroscopy in several solvents, with the equilibrium shifted far towards the enol tautomer. This study reveals the significance of peripheral groups in the stabilization of metastable tautomers in the solid state.