Lanthanide Contraction within a Series of Asymmetric Dinuclear [Ln2] Complexes

A complete isostructural series of dinuclear asymmetric lanthanide complexes has been synthesized by using the ligand 6‐[3‐oxo‐3‐(2‐hydroxyphenyl)propionyl]pyridine‐2‐carboxylic acid (H₃ L ). All complexes have the formula [Ln₂(H L )₂(H₂ L )(NO₃)(py)(H₂O)] (Ln=La ( 1 ), Ce ( 2 ), Pr ( 3 ), Nd ( 4 ), Sm ( 5 ), Eu ( 6 ), Gd ( 7 ), Tb ( 8 ), Dy ( 9 ), Ho ( 10 ), Er ( 11 ), Tm ( 12 ), Yb ( 13 ), Lu ( 14 ), Y ( 15 ); py=pyridine). Complexes of La to Yb and Y have been crystallographically characterized to reveal that the two metal ions are encapsulated within two distinct coordination environments of differing size. Whereas one site maintains the coordination number (nine) through the whole series, the other one increases from nine to ten owing to a change in the coordination mode of an NO₃^? ligand. This series offers a unique opportunity to study in detail the lanthanide contraction within complexes of more than one metal. This analysis shows that various representative parameters proportional to this contraction follow a quadratic decay as a function of the number n of f electrons. Slater’s model for the atomic radii has been used to extract, from these decays, the shielding constant of 4f electrons. The average of O???O distances within the coordination polyhedra shared by both metals and of the Ln???Ln separations follow also a quadratic decay, therefore showing that such dependence holds also for parameters that receive the contribution of two lanthanide ions simultaneously. The magnetic behavior has been studied for all nondiamagnetic complexes. It reveals the effect of the spin–orbit coupling and a weak antiferromagnetic interaction between both metals. Photoluminescent studies of all the complexes in the series reveal a single broad emission band in the visible region, which is related to the coordinated ligand. On the other hand, the Nd, Er, and Yb complexes show features in the near‐IR region due to metal‐based transitions.     

Chromo‐Fluorogenic Detection of Nitroaromatic Explosives by Using Silica Mesoporous Supports Gated with Tetrathiafulvalene Derivatives

Three new hybrid gated mesoporous materials ( SN₃‐1 , SNH₂‐2 , and SN₃‐3 ) loaded with the dye [Ru(bipy)₃]²⁺ (bipy=bipyridine) and capped with different tetrathiafulvalene (TTF) derivatives (having different sizes and shapes and incorporating different numbers of sulfur atoms) have been prepared. The materials SN₃‐1 and SN₃‐3 are functionalized on their external surfaces with the TTF derivatives 1 and 3 , respectively, which were attached by employing the “click” chemistry reaction, whereas SNH₂‐2 incorporates the TTF derivative 2 , which was anchored to the solid through an amidation reaction. The final gated materials have been characterized by standard techniques. Suspensions of these solids in acetonitrile showed “zero release”, most likely because of the formation of dense TTF networks around the pore outlets. The release of the entrapped [Ru(bipy)₃]²⁺ dye from SN₃‐1 , SNH₂‐2 , and SN₃‐3 was studied in the presence of selected explosives (Tetryl, TNT, TNB, DNT, RDX, PETN, PA, and TATP). SNH₂‐2 showed a fairly selective response to Tetryl, whereas for SN₃‐1 and SN₃‐3 dye release was found to occur with Tetryl, TNT, and TNB. The uncapping process in the three materials can be ascribed to the formation of charge‐transfer complexes between the electron‐donating TTF units and the electron‐accepting nitroaromatic explosives. Finally, solids SNH₂‐2 and SN₃‐1 have been tested for Tetryl detection in soil with good results, pointing toward a possible use of these or similar hybrid capped materials as probes for the selective chromo‐fluorogenic detection of nitroaromatic explosives.     

A Closer Look at Spontaneous Mirror Symmetry Breaking in Aldol Reactions

The aldol reaction between acetone and 4‐nitrobenzaldehyde run in the nominal absence of any enantioselective catalyst was monitored by chiral HPLC with the aid of an internal standard. The collected data show the presence of a detectable initial enantiomeric excess of the aldol product in the early stages of the reaction in about 50 % of the experiments. Only a small fraction of the reaction contained the non‐racemic aldol product after 24 h. This temporary emergence of natural optical activity could be the signature of a coupled reaction network that leads to a spontaneous mirror‐symmetry‐breaking process, which originates at very low conversions (i.e., strongly depends on events taking place at the very first stages of the process). The reaction is not autocatalytic in the aldol product, which rules out a simple Frank‐type reaction network as the source of the observed symmetry breaking. On the other hand, the isolation and characterisation of a double‐aldol adduct suggested a reaction network that involved both indirect autocatalysis and indirect mutual inhibition between the enantiomers of the reaction product.     

A Sequential Method to Prepare Polymorphs and Solvatomorphs of [Fe(1,3‐bpp)2](ClO4)2⋅nH2O (n=0, 1, 2) with Varying Spin‐Crossover Behaviour

Two polymorphs of the spin crossover (SCO) compound [Fe(1,3‐bpp)₂](ClO₄)₂ ( 1 and 2 ; 1,3‐bpp=2‐(pyrazol‐1‐yl)‐6‐(pyrazol‐3‐yl)pyridine) were prepared using a novel, stepwise procedure. Crystals of 1 deposit from dry solvents, while 2 is obtained from a solid‐state procedure, by sequentially removing lattice H₂O molecules from the solvatomorph [Fe(1,3‐bpp)₂](ClO₄)₂?2 H₂O ( 2 ?2 H₂O), using single‐crystal‐to‐single‐crystal (SCSC) transformations. Hydrate 2 ?2 H₂O is obtained through the same reaction as 1 , now with 2.5 % of water added. Compounds 2 and 2 ?2 H₂O are unstable in the atmosphere and absorb or lose one equivalent of water, respectively, to both yield the stable solvatomorph [Fe(1,3‐bpp)₂](ClO₄)₂?H₂O ( 2 ?H₂O), also following SCSC processes. The four derivatives have been characterised by single‐crystal X‐ray diffraction (SCXRD). Furthermore, the homogeneity of the various compounds as well as their SCSC interconversions have been confirmed by powder X‐ray diffraction (PXRD). Polymorphs 1 and 2 exhibit abrupt SCO behaviour near room temperature with T_1/2↑=279/316 K and T_1/2↓=276/314 K (near 40 K of shift) and different cooperativity.     

Structure of triplex DNA in the gas phase

Extensive (more than 90 microseconds) molecular dynamics simulations complemented with ion-mobility mass spectrometry experiments have been used to characterize the conformational ensemble of DNA triplexes in the gas phase. Our results suggest that the ensemble of DNA triplex structures in the gas phase is well-defined over the experimental time scale, with the three strands tightly bound, and for the most abundant charge states it samples conformations only slightly more compact than the solution structure. The degree of structural alteration is however very significant, mimicking that found in duplex and much larger than that suggested for G-quadruplexes. Our data strongly supports that the gas phase triplex maintains an excellent memory of the solution structure, well-preserved helicity, and a significant number of native contacts. Once again, a linear, flexible, and charged polymer as DNA surprises us for its ability to retain three-dimensional structure in the absence of solvent. Results argue against the generally assumed roles of the different physical interactions (solvent screening of phosphate repulsion, hydrophobic effect, and solvation of accessible polar groups) in modulating the stability of DNA structures.     

Mesoporous aluminum phosphite

High surface area pure mesoporous aluminum-phosphorus oxide-based derivatives have been synthesized through an S⁺I⁻ surfactant-assisted cooperative mechanism by means of a one-pot preparative procedure from aqueous solution and starting from aluminum atrane complexes and phosphoric and/or phosphorous acids. A soft chemical extraction procedure allows opening the pore system of the parent as-prepared materials by exchanging the surfactant without mesostructure collapse. The nature of the pore wall can be modulated from mesoporous aluminum phosphate (ALPO) up to total incorporation of phosphite entities (mesoporous aluminum phosphite), which results in a gradual evolution of the acidic properties of the final materials. While phosphate groups in ALPO act as network building blocks (bridging Al atoms), the phosphite entities become basically attached to the pore surface, what gives practically empty channels. The mesoporous nature of the final materials is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption–desorption isotherms. The materials present regular unimodal pore systems whose order decreases as the phosphite content increases. NMR spectroscopic results confirm the incorporation of oxo-phosphorus entities to the framework of these materials and also provide us useful information concerning the mechanism through which they are formed.     

Aqua bridged Cu2 dimer of a heptadentate N4O3 coordinating ligand: Synthesis,structure and magnetic properties

The N₄O₃ coordinating heptadentate imidazolidinyl phenolate ligand, H₃L (2-(2′-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) forms with Cu(II) a rare aqua bridged complex [{Cu₂(μ-L)(μ-H₂O)}₂](ClO₄)₂ · 4.5H₂O (1 · 4.5H₂O). Complex 1 · 4.5H₂O contains two crystallographically different but chemically equivalent dinuclear [Cu₂(μ-L)(μ-H₂O)]⁺ cationic units in the asymmetric unit. The copper atoms of each dinuclear unit are in a distorted square-pyramidal environment and are held together by phenolate, imidazolidinyl and aqua bridges with a Cu···Cu separation of av. 3.34 Å. The compound exhibits a very weak antiferromagnetic exchange interaction (J = −0.77 cm⁻¹, ? = −2 J?₁?₂) between the two copper(II) (S = 1/2) ions. The ¹H NMR spectrum of the complex shows a total of 17 hyperfine shifted peaks, as expected from the idealized C_s symmetry of the compound, spread over a very large window of chemical shift, spanning about 250 ppm. The complex, having an appropriate intermetallic separation for catechol binding, shows catecholase like activity in MeCN at 25 °C, with the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ).     

Ferromagnetic NiII Discs

A family of planar disc‐like hexa‐, octa‐ and decametallic Ni^II complexes exhibit dominant ferromagnetic exchange. The deca‐ and octametallic clusters [Ni^II₁₀(tmp)₂(N₃)₈(acac)₆(MeOH)₆] ( 1 , H₃tmp=1,1,1‐tris(hydroxymethyl)propane; acac=acetylacetonate) and [Ni^II₈(thme)₂(O₂CPh)₄(Cl)₆(MeCN)₆(H₂O)₂] ( 2 , H₃thme=1,1,1‐tris(hydroxymethyl)ethane) represent rare examples of Ni^II‐based single‐molecule magnets, and [Ni^II₁₀] ( 1 ) possesses the largest barrier to magnetisation reversal of any Ni^II single‐molecule magnet to date.     

Large monolithic silica-based macrocellular foams with trimodal pore system

Silica-based materials with hierarchical pore systems at three different length scales (small mesopores-large mesopores-macropores) have been prepared through a nanotectonic approach by using mesoporous nanoparticles as building blocks; the resulting materials present a highly accessible foam-like architecture and can be prepared as large monoliths.     

A fast passive and planar liquid sample micromixer

A novel microdevice for passively mixing liquid samples based on surface tension and a geometrical mixing chamber is presented. Due to the laminar flow regime on the microscale, mixing becomes difficult if not impossible. We present a micromixer where a constantly changing time dependent flow pattern inside a two sample liquid plug is created as the plug simply passes through the planar mixer chamber. The device requires no actuation during mixing and is fabricated using a single etch process. The effective mixing of two coloured liquid samples is demonstrated.