Slow Magnetization Relaxation in a Family of Triangular {CoIII 2 LnIII } Clusters: The Effect of Diamagnetic CoIII Ions on the LnIII Magnetic Dynamics.

The first use of the Schiff base chelate N-naphthalidene-o-aminophenol (naphH2 ) in Co/Ln chemistry has afforded a family of isostructural [CoIII 2 LnIII (OMe)2 (naph)2 (O2 CMe)3 (MeOH)2 ] (Ln=Tb, Dy and Er) complexes, revealing a rare {CoIII 2 Ln(µ3 -OMe)}8+ triangular core composed of two diamagnetic CoIII ions and a 4f-ion with slightly distorted square antiprismatic geometry. Alternating current (ac) magnetic susceptibility studies revealed that {Co2 Dy}, and its magnetic diluted analogue {Co2 Dy0.05 Y0.95 }, behave as mononuclear single-molecule magnets (SMMs) with similar energy barriers for the magnetization reversal, Ueff , of ~85-90 K. SMM properties were also detected for {Co2 Er}, with the compound exhibiting a Ueff of 18.7 K under an applied magnetic field of 800 Oe. To interpret the experimental magnetic results, ab initio CASSCF/RASSI-SO and DFT calculations were performed as a means of exploring the single-ion characteristics of LnIII ions and comprehend the role of the diamagnetic CoIII ions in the magnetization relaxation of the three heterometallic compounds.

Ionic Liquid-Based Polyoxometalate Incorporated at ZIF-8: A Sustainable Catalyst to Combine Desulfurization and Denitrogenation Processes.

An effective and sustainable process capable of simultaneously execute desulfurization and denitrogenation of fuels is in fact an actual necessity in the refinery industry. The key to achieve this goal is the parallel oxidation of sulfur and nitrogen compounds present in fuels, which is only achieved by an active and recovered catalyst. A novel heterogeneous catalyst was successfully prepared by the encapsulation of an imidazolium-based polyoxometalate (POM) into a ZIF-8 framework ([BMIM]PMo12@ZIF-8). This composite material revealed exceptional catalytic efficiency to concurrently proceed with the oxidative desulfurization and denitrogenation of a multicomponent model fuel containing various sulfur and nitrogen compounds. A complete removal of all these compounds was achieved after only one hour and the catalyst system was able to be reused for ten consecutive cycles without loss of efficiency. In fact, an ionic liquid POM was incorporated in the ZIF-8 for the first time, and this composite compound was originally applied as a catalyst for simultaneous oxidative desulfurization and denitrogenation processes.

Membrane-Supported Layered Coordination Polymer as an Advanced Sustainable Catalyst for Desulfurization.

The application of a catalytic membrane in the oxidative desulfurization of a multicomponent model diesel formed by most refractory sulfur compounds present in fuel is reported here for the first time. The catalytic membrane was prepared by the impregnation of the active lamellar [Gd(H4nmp)(H2O)2]Cl·2H2O (UAV-59) coordination polymer (CP) into a polymethyl methacrylate (PMMA, acrylic glass) supporting membrane. The use of the catalytic membrane in the liquid-liquid system instead of a powder catalyst arises as an enormous advantage associated with the facility of catalyst handling while avoiding catalyst mass loss. The optimization of various parameters allowed to achieve a near complete desulfurization after 3 h under sustainable conditions, i.e., using an aqueous H2O2 as oxidant and an ionic liquid as extraction solvent ([BMIM]PF6, 1:0.5 ratio diesel:[BMIM]PF6). The performance of the catalytic membrane and of the powdered UAV-59 catalyst was comparable, with the advantage that the former could be recycled successfully for a higher number of desulfurization cycles without the need of washing and drying procedures between reaction cycles, turning the catalytic membrane process more cost-efficient and suitable for future industrial application.

From Discrete Complexes to Metal-Organic Layered Materials: Remarkable Hydrogen Bonding Frameworks.

A series of metal-organic coordination complexes based on alkaline-earth metal centers [Mg(II), Ca(II), and Ba(II)] and the ligand 5-aminoisophthalate (aip2-) revealed notable structural diversity, both in the materials' dimensionality and in their hydrogen bonding networks: [Mg(H2O)6]∙[Mg2(Haip)(H2O)10]∙(Haip)∙3(aip)∙10(H2O) (1) and [Mg(aip)(phen)(H2O)2]∙(H2O) (2) were isolated as discrete complexes (0D); [Ca(aip)(H2O)2]∙(H2O) (3), [Ca(aip)(phen)(H2O)2]∙(phen)∙(H2O) (4), and [Ba2(aip)2(phen)2(H2O)7]∙2(phen)∙2(H2O) (5) revealed metal-organic chain (1D) structures, while the [Ba(aip)(H2O)] (6) showed a metal-organic layered (2D) arrangement. Furthermore, most of these metal-organic coordination materials revealed interesting thermal stability properties, being stable at temperatures up to 450 °C.

An Effective Hybrid Heterogeneous Catalyst to Desulfurize Diesel: Peroxotungstate@Metal-Organic Framework.

A peroxotungstate composite comprising the chromium terephthalate metal-organic framework MIL-101(Cr) and the Venturello peroxotungstate [PO4{WO(O2)2}4]3- (PW4) has been prepared by the impregnation method. The PW4@MIL-101(Cr) composite presents high catalytic efficiency for oxidative desulfurization of a multicomponent model diesel containing the most refractory sulfur compounds present in real fuels (2000 ppm of total S). The catalytic performance of this heterogeneous catalyst is similar to the corresponding homogeneous PW4 active center. Desulfurization efficiency of 99.7% was achieved after only 40 min at 70 °C using H2O2 as an oxidant and an ionic liquid as an extraction solvent ([BMIM]PF6, 2:1 model diesel/[BMIM]PF6). High recycling and reusing capacity was also found for PW4@MIL-101(Cr), maintaining its activity for consecutive oxidative desulfurization cycles. A comparison of the catalytic performance of this peroxotungstate composite with others previously reported tungstate@MIL-101(Cr) catalysts indicates that the presence of active oxygen atoms from the peroxo groups promotes a higher oxidative catalytic efficiency in a shorter reaction time.

Subppm Amine Detection via Absorption and Luminescence Turn-On Caused by Ligand Exchange in Metal Organic Frameworks.

Luminescent metal-organic frameworks (LMOFs) are promising materials for lighting and sensing applications. Herein, exposure of the highly luminescent Zn2(bpdc)2(bpee) MOF (H2bpdc = 4,4'-biphenyldicarboxylic acid and bpee = 1,2-bipyridylethene) to subppm amine contents turns on a new absorption band unambiguously ascribed to free bpee molecules concomitant with the gradual appearance of a new photoluminescence band at shorter wavelengths. These findings combined with Fourier-transform infrared spectra, powder X-ray diffraction and thermogravimetric analysis of exposed LMOF powders confirm that bpee ligands are exchanged by amines and released inside the LMOF, triggering absorption and luminescence features which can be exploited for highly sensitive amine recognition. This principle was demonstrated in mixed matrix membranes (MMMs) prepared by a simple solvent-free method consisting of mixing Zn2(bpdc)2(bpee) with dimethylvinyl-terminated dimethylsiloxane and dimethylhydrogen siloxane. This method enabled the production of free-standing, permeable, and highly transparent MMMs which showed enormous potential and sensitivity to the detection of amines in gas phase and aqueous medium.

Synthesis of Pyridyl and N-Methylpyridinium Analogues of Rosamines: Relevance of Solvent and Charge on Their Photophysical Properties.

A series of pyridyl analogues of rosamines was prepared by employing two methodologies: (i) the conventional-heating condensation of a pyridinecarboxaldehyde with 3-(diethylamino)phenol in propionic acid, and (ii) the novel ohmic-heating assisted condensation under "on water" conditions, followed by oxidation. The 4-pyridyl substituted rosamine was further converted into the N-methylpyridinium derivative through N-alkylation using methyl iodide. The influence of the position and cationization of the nitrogen atom of the pyridyl ring in the physicochemical properties of fluorophores was investigated by 1 H, 13 C, 15 N NMR spectral analysis, UV/Vis and fluorescence spectroscopy, single-crystal X-ray diffraction (4-pyridyl and N-methylpyridinium derivatives) and thermal-behavior analysis. Curiously, for ethanolic solutions of 4-pyridyl and N-methylpyridinium derivatives an extinction of color and fluorescence over time was observed. This phenomenon was further studied and the data revealed that it is the result of nucleophilic addition of ethoxide ion to the central 9-position of the xanthene. The kinetics of the process is slower for the 4-pyridyl rosamine, which emphasizes the importance of the charge in the N-methylpyridinium analogue in the reactivity of the molecule towards a nucleophile agent. This phenomenon is reversible, meaning that the compounds can be rapidly recovered by decreasing the pH, opening new avenues in the sensing applications of this class of rosamines.

Multifunctionality in Two Families of Dinuclear Lanthanide(III) Complexes with a Tridentate Schiff-Base Ligand.

The employment of N-(2-carboxyphenyl)salicylideneimine in 4f metal chemistry has led to two families of dinuclear complexes depending on the lanthanide(III) used. Representative members exhibit interesting magnetic, optical, and catalytic properties.

Large Energy Barrier and Magnetization Hysteresis at 5 K for a Symmetric {Dy2} Complex with Spherical Tricapped Trigonal Prismatic DyIII Ions.

The introduction of the Schiff base ligand N-salicylidene-2-amino-5-chlorobenzoic acid (sacbH2) in 4f-metal chemistry has afforded a new dinuclear complex, [Dy2(NO3)4(sacbH)2(H2O)2(MeCN)2] (1), with the metal ions adopting a rare spherical tricapped trigonal prismatic coordination geometry. The deprotonated phenoxido O atoms of the organic chelate occupy the axial triangular faces of the prism and were found to be very close to the main anisotropy axes of the two DyIII ions. As a result, the {DyIII2} compound exhibits frequency- and temperature-dependent out-of-phase ac signals below ∼25 K in the absence of a static dc field, yielding an energy barrier of 109.3(1) K for the reversal of magnetization. Fast and efficient quantum tunneling of magnetization, attributed to the strong tails of signals below ∼15 K, was suppressed through the application of a small dc field, yielding entirely visible χM″ signals below 27 K. Single-crystal magnetic hysteresis studies confirmed the single-molecule magnet (SMM) behavior of 1; the hysteresis loops appear at temperatures below ∼5 K, which is one of the highest blocking temperatures in the field of 4f-SMMs to date. This joint magneto-structural and ab initio study demonstrates the ability of more common coordination numbers (i.e., 9), but with rare coordination geometries (i.e., spherical tricapped trigonal prismatic), to promote axiality that enhances the molecular anisotropy and subsequently the magnetization dynamics of the system.

Structural Diversities in Heterometallic Mn-Ca Cluster Chemistry from the Use of Salicylhydroxamic Acid: {MnIII4Ca2}, {MnII/III6Ca2}, {MnIII/IV8Ca}, and {MnIII8Ca2} Complexes with Relevance to Both High- and Low-Valent States of the Oxygen-Evolving Complex.

One-pot reactions between the [Mn3O(O2CPh)6(py)x]+/0 triangular precursors and either CaBr2·xH2O or CaCl2·6H2O, in the presence of salicylhydroxamic acid (shaH2), have afforded the heterometallic complexes [MnIII4Ca2(O2CPh)4(shi)4(H2O)3(Me2CO)] (1) and (pyH)[MnII2MnIII4Ca2Cl2(O2CPh)7(shi)4(py)4] (2), respectively, in good yields. Further reactions but using a more flexible synthetic scheme comprising the Mn(NO3)2·4H2O/Ca(NO3)2·4H2O and Mn(O2CPh)2·2H2O/Ca(ClO4)2·4H2O "metal blends" and shaH2, in the presence of external base NEt3, led to the new complexes (NHEt3)2[MnIII4MnIV4Ca(OEt)2(shi)10(EtOH)2] (3) and (NHEt3)4[MnIII8Ca2(CO3)4(shi)8] (4), respectively. In all reported compounds, the anion of the tetradentate (N,O,O,O)-chelating/bridging ligand salicylhydroxime (shi3-), resulting from the in situ metal-ion-assisted amide-iminol tautomerism of shaH2, was found to bridge both Mn and Ca atoms. Complexes 1-4 exhibit a variety of different structures, metal stoichiometries, and Mn oxidation-state descriptions; 1 possesses an overall octahedral metal arrangement, 2 can be described as a Mn4Ca2 octahedron bound to an additional Mn2 unit, 3 consists of a Mn8 "ring" surrounding a CaII atom, and 4 adopts a rectangular cuboidal motif of eight Mn atoms accommodating two CaII atoms. Solid-state direct-current magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the Mn centers, leading to S = 0 spin ground-state values for all complexes. From a bioinorganic chemistry perspective, the reported compounds may demonstrate some relevance to both high-valent scheme (3) and lower-oxidation-level species (1, 2, and 4) of the catalytic cycle of the oxygen-evolving complex.

"Molecular Nanoclusters": A 2-nm-Sized {Mn29} Cluster with a Spherical Structure.

The comproportionation reaction between MnII and MnVII sources in the presence of 3,3-dimethylacrylic acid and azides has led to a new {Mn29} molecular cluster with a spherical structure and dimensions of ∼2.2 nm, comparable in size to the smallest classical and magnetic nanoparticles.

"Ligands-with-Benefits": Naphthalene-Substituted Schiff Bases Yielding New Ni(II) Metal Clusters with Ferromagnetic and Emissive Properties and Undergoing Exciting Transformations.

The initial employment of the fluorescent bridging ligand N-naphthalidene-2-amino-5-chlorobenzoic acid (nacbH2) in metal cluster chemistry has led to new Ni12 (1) and Ni5 (2) clusters with wheel-like and molecular-chain topologies, respectively. The doubly-deprotonated nacb(2-) ligands were found to adopt four different coordination modes within 1 and 2. The nature of the ligand has also allowed unexpected organic transformations to occur and ferromagnetic and emission behaviors to emerge. The combined work demonstrates the ability of some "ligands-with-benefits" to yield beautiful structures with exciting topologies and interesting physicochemical properties.

Design of a Water Soluble Fluorescent 3-Hydroxy-4-Pyridinone Ligand Active at Physiological pH Values.

In the present work we report the structure and the spectroscopic characterization of a new fluorescent 3-hydroxy-4-pyridinone ligand D-3,4-HPO. The synthesis of the compound was performed in two steps, which involve the reaction of the commercially available fluorophore dansyl chloride with a 3-hydroxy-4-pyridinone chelating unit and further deprotection. The new fluorescent chelator was characterized in the solid state by single-crystal X-ray diffraction and in solution by NMR, MS, absorption and fluorescence spectroscopies. The analysis of the variation of the absorption spectrum with pH allowed the determination of four pK a values (pK a1  = 3.50, pK a2  = 4.50, pK a3  = 9.60, pK a4  = 10.20) and establishment of the corresponding distribution diagram. The study of the fluorescence properties of the ligand show that in the pH range between 4 and 9 the fluorescence intensity is constant and has its maximum value thus allowing its further use at physiological pH values. The interaction of the ligand with copper(II) was accessed by fluorescence spectroscopy in MOPS buffer and the results show that the presence of copper(II) quenches the fluorescence of the ligand in ca 94 % at a ligand: metal ratio of 2:1. The latter result is consistent with the formation of a copper(II) complex with the bidentate ligand, as confirmed by the EPR spectroscopy. Graphical Abstract New water soluble fluorescent ligand active at physiological pH values.

The Influence of the Amide Linkage in the Fe(III) -Binding Properties of Catechol-Modified Rosamine Derivatives.

The two new fluorescent ligands RosCat1 and RosCat2 contain catechol receptors connected to rosamine platforms through an amide linkage and were synthesized by using microwave-assisted coupling reactions of carboxyl- or amine-substituted rosamines with the corresponding catechol units and subsequent deprotection. RosCat1 possesses a reverse amide, whereas RosCat2 has the usual oriented amide bond (HNCO vs. CONH, respectively). The ligands were characterized by means of NMR spectroscopy, mass-spectrometry, and DFT calculations and X-ray crystallography studies for RosCat1. The influence of the amide linkage on the photophysical properties of the fluorescent ligands was assessed in different solvents and showed a higher fluorescence quantum yield for RosCat1. The coordination chemistry of these ligands with a Fe(III) center has been rationalized by mass-spectrometric analysis and semiempirical calculations. Octahedral Fe(III) complexes were obtained by the chelation of three RosCat1 or RosCat2 ligands. Interestingly, the unconventional amide connectivity in RosCat1 imposes the formation of an eight-membered ring on the chelate complex through a "salicylate-type" mode of coordination.

Emissive {Mn4(III)Ca} clusters with square pyramidal topologies: syntheses and structural, spectroscopic, and physicochemical characterization.

The one-pot reactions between Mn(ClO4)2·6H2O, Ca(ClO4)2·4H2O, and the potentially tetradentate (N,O,O,O) chelating/bridging ligand salicylhydroxime (shiH3), resulting from the in situ metal ion-assisted amide-iminol tautomerism of salicylhydroxamic acid in the presence of various fluorescence carboxylate groups and base NEt3, afford a family of structurally similar {Mn4Ca} clusters with distorted square pyramidal topology. The reported complexes (NHEt3)2[Mn4Ca(L1)4(shi)4] (1), (NHEt3)2[Mn4Ca(L2)4(shi)4] (2), (NHEt3)5[Mn4Ca(L2)4(shi)4(shiH2)2](ClO4) (3), and (NHEt3)2[Mn4Ca(L3)4(shi)4] (4) contain a similar [Mn4Ca(µ-NO)4](10+) core of four Mn(III) atoms at the square base and a Ca(II) atom occupying the apical site. Peripheral ligation about the core is provided by four η(1):η(1):µ carboxylate groups of the anions of 2-naphthoic acid (L1(-)), 9-anthracenecarboxylic acid (L2(-)), and 1-pyrenecarboxylic acid (L3(-)). Solid-state direct current magnetic susceptibility studies revealed the presence of predominant antiferromagnetic exchange interactions between the 4 Mn(III) centers, which were primarily quantified by using a simple 1-J fit model to give S = 0 spin ground states with low-lying excited states close in energy to the ground state. Solution studies in solvent MeCN were carried out on all complexes and confirmed their structural integrity. Cyclic voltammetry studies showed a similar well-defined reversible oxidation and an irreversible reduction for all complexes, thus establishing their redox potency and electrochemical efficiency. Emission studies in solution proved the optical activity of all compounds, with the observed "blue" emission peaks attributed to the π-rich chromophores of the organic fluorescence ligands. The combined results demonstrate the ability of shiH3 and fluorescence carboxylates to yield new heterometallic Mn/Ca clusters with (i) the same Mn/Ca ratio as the oxygen-evolving complex of Photosystem II, (ii) structural stability in solution, and (iii) a pronounced redox and optical activity.

Isoxazolidine-fused meso-tetraarylchlorins as key tools for the synthesis of mono- and bis-annulated chlorins.

The microwave-assisted catalytic hydrogenation of the isoxazolidine-fused meso-tetrakis(pentafluorophenyl)chlorin afforded directly a mono-annulated chlorin with a singular 1-methyl-2,3-dihydro-1H-benzo[b]azepine ring that resulted from the cleavage of the isoxazolidine N-O bond followed by an intramolecular nucleophilic aromatic substitution of an o-F atom. The subsequent treatment of the mono-annulated chlorin with NaH induced a second intramolecular nucleophilic aromatic substitution, generating a bis-annulated chlorin having an additional 2H-pyran ring.

Multidimensional transition metal complexes based on 3-amino-1H-1,2,4-triazole-5-carboxylic acid: from discrete mononuclear complexes to layered materials.

The synthesis and structural characterization of five transition metal complexes with different dimensionality and incorporating residues of 3-amino-1H-1,2,4-triazole-5-carboxylic acid (H2atrc) is reported: [Zn(Hatrc)2(H2O)] (1), [Mn(Hatrc)2(H2O)2]·2H2O (2), [Fe2(Hatrc)4(OH)2]·6H2O (3), [Cd(Hatrc)2(H2O)]n (4), and [Mn(atrc)(H2O)]n·nH2O (5). These materials could be prepared from solution (1-3), diffusion (4), or hydrothermal reactions (5) with various anions and L:M ratios. Structural details were revealed by single crystal X-ray diffraction. The discrete units composing compounds 1-3, the polymeric 1D chain of 4 and the 2D layer of 5 are further extended into 3D supramolecular architectures through the formation of hydrogen bonds.

New classes of ferromagnetic materials with exclusively end-on azido bridges: from single-molecule magnets to 2 D molecule-based magnets.

A new, flexible synthetic route, which does not require the co-presence of any organic chelating/bridging ligand but only the "key" precursor Me3SiN3, has been discovered and led to a new class of inorganic materials containing exclusively end-on azido bridges; the reported 3d-metal clusters and coordination polymers exhibit ferromagnetic, single-molecule magnet, and long-range magnetic ordering properties.

Tetranuclear lanthanide(III) complexes with a zigzag topology from the use of pyridine-2,6-dimethanol: synthetic, structural, spectroscopic, magnetic and photoluminescence studies.

Reaction between Ln(NO3)3·xH2O (x = 5 or 6) and the potentially tridentate (N,O,O) chelating/bridging ligand pyridine-2,6-dimethanol (pdmH2), in the presence of base NEt3, affords a family of isostructural tetranuclear [Ln(III)4(NO3)2(pdmH)6(pdmH2)2](NO3)4 (Ln(III) = Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Yb(III)) complexes with a rare zigzag topology. All complexes contain a [Ln4(µ-OR)6](6+) core with bridging ligation provided by the alkoxido arms of six η(1):η(1):η(2):µ pdmH(-) groups. The Ln(III) ions are eight coordinate with distorted geometries. Direct current magnetic susceptibility studies revealed predominant weak antiferromagnetic exchange interactions between the metal centers, which were quantified in the case of isotropic Gd(III)4 to give J = -0.09(1) cm(-1) and g = 2.00(1). The observation of out-of-phase (χ″M) ac susceptibility signals suggested that the Dy(III)4 analogue might be a molecular nanomagnet. Solid-state photoluminescence studies showed that the Eu(III)4 and Tb(III)4 compounds exhibit intense, sharp, and narrow emission bands in the red and green visible regions, respectively, which arise from the characteristic (5)D0 → (7)FJ and (5)D4 → (7)FJ transitions. The combined results demonstrate the ability of pdmH2 ligand to yield homometallic 4f clusters with interesting magnetic and optical properties.

Fluorescent naphthalene diols as bridging ligands in Ln(III) cluster chemistry: synthetic, structural, magnetic, and photophysical characterization of Ln(III)8 "Christmas stars".

The initial employment of the fluorescent bridging ligand naphthalene-2,3-diol in 4f-metal coordination chemistry has provided access to a new family of Ln(III)8 clusters with a "Christmas-star" topology, single-molecule magnetism behavior, and ligand-centered emissions.