A Remarkable Solvent Effect on the Nuclearity of Neutral Titanium(IV)‐Based Helicate Assemblies

The spontaneous self‐assembly of a neutral circular trinuclear Ti^IV‐based helicate is described through the reaction of titanium(IV) isopropoxide with a rationally designed tetraphenolic ligand. The trimeric ring helicate was obtained after diffusion of n‐pentane into a solution with dichloromethane. The circular helicate has been characterized by using single‐crystal X‐ray diffraction study, ¹³C CP‐MAS NMR and ¹H NMR DOSY solution spectroscopic, and positive electrospray ionization mass‐spectrometric analysis. These analytical data were compared with those obtained from a previously reported double‐stranded helicate that crystallizes in toluene. The trimeric ring was unstable in a pure solution with dichloromethane and transformed into the double‐stranded helicate. Thermodynamic analysis by means of the PACHA software revealed that formation of the double‐stranded helicates was characterized by ΔH(toluene)=?30 kJ mol^?1 and ΔS(toluene)=+357 J K^?1 mol^?1, whereas these values were ΔH(CH₂Cl₂)=?75 kJ mol^?1 and ΔS(CH₂Cl₂)=?37 J K^?1 mol^?1 for the ring helicate. The transformation of the ring helicate into the double‐stranded helicate was a strongly endothermic process characterized by ΔH(CH₂Cl₂)=+127 kJ mol^?1 and ΔH(n‐pentane)=+644 kJ mol^?1 associated with a large positive entropy change ΔS=+1115 J K^?1?mol^?1. Consequently, the instability of the ring helicate in pure dichloromethane was attributed to the rather high dielectric constant and dipole moment of dichloromethane relative to n‐pentane. Suggestions for increasing the stability of the ring helicate are given.     

Crucial role of the counteranion on the templation of metallomacrocycles and a 3D network: synthesis,characterization, and structural analysis

Two novel supramolecular architectures, [[Ag(2)L(1)(2)][X](2)] with X = CF(3)SO(3)(-) (2a) or X = NO(3)(-) (2b) and [[AgL(1)(2)][X]](n) with X = BF(4)(-) (3), were constructed by self-assembly and obtained in quantitative yields, using AgX as a building block and L(1) as the bridging ligand (L(1) = 1,3-bis(benzimidazol-1-ylmethyl)benzene). The X-ray molecular structures of 2a and 3 are reported. Complex 2a was identified as a metallomacrocycle in which one ligating triflate anion is coordinated to each of the two unsaturated Ag(I) ions. 2a crystallizes in monoclinic unit cell P2(1)/n with a = 9.728(6) A, b = 17.303(4) A, c = 13.268(3) A, beta = 92.52(4) degrees, V = 2231(2) A(3), and Z = 2. Remarkably, the X-ray structure of 2a shows a layered network structure consisting of infinite metallomacrocycles held together through pi-pi interactions between benzimidazole rings. In dramatic contrast, the product 3 prepared from AgBF(4) and L(1) lacks metal-counterion bonding, leading to a supramolecular 3D network with the following three outstanding features: (i) in one dimension, metallomacrocycles containing two Ag centers and two bridging ligands form infinite, double-stranded chains; (ii) neighboring chains are arranged by two distinct pi-pi interactions, one between substituted benzene rings and the other between benzimidazole rings, leading to a 3D structure; (iii) cavities within the 3D network contain BF(4)(-) counteranions. 3 crystallizes in monoclinic unit cell C2/c with a = 25.33(3) A, b = 11.655(6) A, c = 18.466(8) A, beta = 123.00(8) degrees, V = 4572(8) A(3), and Z = 4. Interestingly, electrospray mass spectroscopy suggests in either case that the identified elemental subunit [AgL(1)(2)](+) is the key building block which self-assembles and subsequent anion templation provides either the macrocycles 2a, b or the inorganic polymer 3. Remarkably, in dichloromethane solvent ligand-to-metal stoichiometries of 2:1 in 3 and 1:1 in 2a, b are obtained even with excess ligand, showing the power of metal-anion interactions in determining the overall supramolecular structure. Anion metathesis, showing supramolecular structural rearrangements from 2a to 2b and more spectacularly from 3 to 2b, smoothly occurred. The crucial effect and the nature of coordinating counteranions (BF(4)(-), CF(3)SO(3)(-), NO(3)(-)) on the supermolecule design are presented and discussed.     

Ultrasonic sludge pretreatment under pressure

The objective of this work was to optimize the ultrasound (US) pretreatment of sludge. Three types of sewage sludge were examined: mixed, secondary and secondary after partial methanisation (“digested” sludge). Thereby, several main process parameters were varied separately or simultaneously: stirrer speed, total solid content of sludge (TS), thermal operating conditions (adiabatic vs. isothermal), ultrasonic power input (P_US), specific energy input (ES), and for the first time external pressure. This parametric study was mainly performed for the mixed sludge. Five different TS concentrations of sludge (12–36 g/L) were tested for different values of ES (7000–75,000 kJ/kg_TS) and 28 g/L was found as the optimum value according to the solubilized chemical oxygen demand in the liquid phase (SCOD). P_US of 75–150 W was investigated under controlled temperature and the “high power input – short duration” procedure was the most effective at a given ES. The temperature increase in adiabatic US application significantly improved SCOD compared to isothermal conditions. With P_US of 150 W, the effect of external pressure was investigated in the range of 1–16 bar under isothermal and adiabatic conditions for two types of sludge: an optimum pressure of about 2 bar was found regardless of temperature conditions and ES values. Under isothermal conditions, the resulting improvement of sludge disintegration efficacy as compared to atmospheric pressure was by 22–67% and 26–37% for mixed and secondary sludge, respectively. Besides, mean particle diameter (D[4,3]) of the three sludge types decreased respectively from 408, 117, and 110 μm to about 94–97, 37–42, and 36–40 μm regardless of sonication conditions, and the size reduction process was much faster than COD extraction.     

Modeling the HCOOH/CO2 Electrocatalytic Reaction: When Details Are Key

Our first principles simulations of the electrooxidation of formic acid over nickel identify the reorientation of the formate intermediate and the desorption of CO₂ as the rate‐limiting steps. Although they are not associated with an electron transfer, these barriers are strongly modified when the electrochemical potential is explicitly accounted for and when modeling the influence of the solvent. Hence, such a level of modeling is key to understand the kinetic limitations that penalize the reaction.     

Long-term stability of methylmercury standard solutions in distilled,deionized water

The long-term storage behaviour of methylmercury at different concentrations in distilled, deionized water was studied under various storage conditions. The stability is strongly dependent on concentration, the container material and the storage temperature. Container pretreatment also has an influence. Light seems to have no effect on the stability of methylmercury solutions.     

Splitting the Phosphorus Bridge of 7‐Phosphanorbornadiene Complexes by Fluoride Ion

The reaction of fluoride ion with 7‐phosphanorbornadiene P–W(CO)₅ complexes yields fluorophosphido complexes which, in turn, can attack a second molecule of 7‐phosphanorbornadiene to give a fluorobiphosphine complex. The corresponding anion displays a huge P–P coupling. The structure of the anionic chromium analogue has been investigated by DFT calculations. The P–P bond is relatively short at 2.20 Å and displays a huge polarity suggesting an interesting chemistry. When the 7‐phosphanorbornadiene P‐substituent is 2‐chloroethyl, the attack of the fluoride ion is followed by a cyclization and a reductive dimerization leading to the first known biphosphirane complex.     

Enantiospecific synthesis of delta and lambda [Ru(bpy)(2)ppy](+) and [Ru(bpy)(2)quo](+) (bpy = 2,2'-bipyridine,ppy = phenylpyridine-H(+), quo = 8-hydroxyquinolate): (1)H and (13)C NMR studies and X-ray structure determination of rac-[Ru(bpy)(2)quo]PF(6)

In this paper, we describe the enantiospecific synthesis and the complete characterization of the two hexacoordinated ruthenium(II) monocations [Ru(bpy)(2)ppy](+) and [Ru(bpy)(2)quo](+) (bpy = 2,2'-bipyridine, ppy = phenylpyridine-H(+), quo = 8-hydroxyquinolate) in their enantiomeric Delta and Lambda forms. The corresponding enantiomeric excesses (ee's) are determined by (1)H NMR using pure Delta-Trisphat (tris(tetrachlorobenzenedialato)phosphate(V) anion) as a chiral (1)H NMR shift reagent. A complete (1)H and (13)C NMR study has been carried out on rac-[Ru(bpy)(2)ppy]PF(6) and rac-[Ru(bpy)(2)quo]PF(6). Additionally, the X-ray molecular structure of rac-[Ru(bpy)(2)quo]PF(6) is reported; this latter species crystallizes in the monoclinic C2/c space group (a = 22.079 A, b = 16.874 A, c = 17.533 A, alpha = 90 degrees, beta = 109.08 degrees, gamma = 90 degrees ).     

(Aceto­nitrile)­[2,6‐bis­(pyrazol‐1‐yl)­pyridine](isonicotin­amide)copper(II)–tetra­fluoro­borate–aceto­nitrile (1/2/2)

Molecules of the title compound, [Cu(C₂H₃N)(C₁₁H₉N₅)(C₆H₆N₂O)](BF₄)₂·2C₂H₃N, comprise (aceto­nitrile)[2,6‐bis(pyrazol‐1‐yl)­pyridine](isonicotin­amide)copper(II) cations, tetra­fluoro­borate anions and lattice aceto­nitrile mol­ecules. The cations have distorted square‐pyramidal geometries in which the N₃‐donor, viz. 2,6‐bis­(pyrazol‐1‐yl)­pyridine, and the N‐donor, viz. the isonicotin­amide ligand, occupy the four basal positions, with the coordinated aceto­nitrile N‐donor atom occupying the apical position. Pairs of cations are linked by N—H?F hydrogen bonds through tetra­fluoro­borate anions, forming centrosymmetric dimers, which are further linked by C—H?O hydrogen bonds into two‐dimensional undulating sheets, three of which interpenetrate to generate a two‐dimensional network.     

Occupancy of the sodalite cages in the blue ultramarine pigments

A quantitative EPR study of blue ultramarine pigments has been performed in order to determine the concentration of the S(3)(-) chromophore. Copper sulfate CuSO(4) x 5H(2)O has been used as a standard, while a ruby crystal was used as an inner standard to take into account the changes of the quality factor of the cavity. These experiments show that, in the most-colored pigments, less than half of the sodalite cages are occupied by a S(3)(-) radical. In other experiments, it has been shown that the blue ultramarine pigments can be significantly modified by heating under a dynamic vacuum. The concentrations of S(3)(-) and S(2)(-), as deduced from EPR and Raman experiments, are increased after this type of treatment. These changes imply that sulfur species are transformed into S(3)(-) or S(2)(-) during this treatment. It is discussed that these sulfur species could be S(2)(-).