Mixed-Valent Trinuclear CoIII-CoII-CoIII Complex with 1,3-Bis(5-chlorosalicylideneamino)-2-propanol

A mixed-valent trinuclear complex with 1,3-bis(5-chlorosalicylideneamino)-2-propanol (H₃clsalpr) was synthesized, and the crystal structure was determined by the single-crystal X-ray diffraction method at 90 K. The molecule is a trinuclear Co^III-Co^II-Co^III complex with octahedral geometries, having a tetradentate chelate of the Schiff-base ligand, bridging acetate, monodentate acetate coordination to each terminal Co³⁺ ion and four bridging phenoxido-oxygen of two Schiff-base ligands, and two bridging acetate-oxygen atoms for the central Co²⁺ ion. The electronic spectral feature is consistent with the mixed valent Co^III-Co^II-Co^III. Variable-temperature magnetic susceptibility data could be analyzed by consideration of the axial distortion of the central Co²⁺ ion with the parameters Δ = –254 cm⁻¹, λ = –58 cm⁻¹, κ = 0.93, tip = 0.00436 cm³ mol⁻¹, θ = –0.469 K, g_z = 6.90, and g_x = 2.64, in accordance with a large anisotropy. The cyclic voltammogram showed an irreversible reduction wave at approximately −1.2 V·vs. Fc/Fc⁺, assignable to the reduction of the terminal Co³⁺ ions.     

Entropy directs the self-assembly of supramolecular palladium coordination macrocycles and cages

The self-assembly of palladium-based cages is frequently rationalized via the cumulative enthalpy (ΔH) of bonds between coordination nodes (M, i.e., Pd) and ligand (L) components. This focus on enthalpic rationale limits the complete understanding of the Gibbs free energy (ΔG) for self-assembly, as entropic (ΔS) contributions are overlooked. Here, we present a study of the M₂^linL₃ intermediate species (M = dinitrato(N,N,N′,N′-tetramethylethylenediamine)palladium(ii), ^linL = 4,4′-bipyridine), formed during the synthesis of triangle-shaped (M₃^linL₃) and square-shaped (M₄^linL₄) coordination macrocycles. Thermochemical analyses by variable temperature (VT) ¹H-NMR revealed that the M₂^linL₃ intermediate exhibited an unfavorable (relative) ΔS compared to M₃^linL₃ (triangle, ΔTΔS = +5.22 kcal mol⁻¹) or M₄^linL₄ (square, ΔTΔS = +2.37 kcal mol⁻¹) macrocycles. Further analysis of these constructs with molecular dynamics (MD) identified that the self-assembly process is driven by ΔG losses facilitated by increases in solvation entropy (ΔS_solv, i.e., depletion of solvent accessible surface area) that drives the self-assembly from “open” intermediates toward “closed” macrocyclic products. Expansion of our computational approach to the analysis of self-assembly in Pd_n^benL_2n cages (^benL = 4,4''-(5-ethoxy-1,3-phenylene)dipyridine), demonstrated that ΔS_solv contributions drive the self-assembly of both thermodynamic cage products (i.e., Pd₁₂^benL₂₄) and kinetically-trapped intermediates (i.e., Pd₈^cL₁₆).

These studies demonstrate that ΔS drives the self-assembly of supramolecular palladium-based coordination macrocycles and cages. As this ΔS contribution arises from solvation, these findings broadly reflect the thermodynamic drive of self-assembly to form compact structures.     

A small-molecule organic ferroelectric with piezoelectric voltage coefficient larger than that of lead zirconate titanate and polyvinylidene difluoride

Piezoelectric materials that generate electricity when deforming are ideal for many implantable medical sensing devices. In modern piezoelectric materials, inorganic ceramics and polymers are two important branches, represented by lead zirconate titanate (PZT) and polyvinylidene difluoride (PVDF). However, PVDF is a nondegradable plastic with poor crystallinity and a large coercive field, and PZT suffers from high sintering temperature and toxic heavy element. Here, we successfully design a metal-free small-molecule ferroelectric, 3,3-difluorocyclobutanammonium hydrochloride ((3,3-DFCBA)Cl), which has high piezoelectric voltage coefficients g₃₃ (437.2 × 10⁻³ V m N⁻¹) and g₃₁ (586.2 × 10⁻³ V m N⁻¹), a large electrostriction coefficient Q₃₃ (about 4.29 m⁴ C⁻²) and low acoustic impedance z₀ (2.25 × 10⁶ kg s⁻¹ m⁻²), significantly outperforming PZT (g₃₃ = 34 × 10⁻³ V m N⁻¹ and z₀ = 2.54 × 10⁷ kg s⁻¹ m⁻²) and PVDF (g₃₃ = 286.7 × 10⁻³ V m N⁻¹, g₃₁ = 185.9 × 10⁻³ V m N⁻¹, Q₃₃ = 1.3 m⁴ C⁻², and z₀ = 3.69 × 10⁶ kg s⁻¹ m⁻²). Such a low acoustic impedance matches that of the body (1.38–1.99 × 10⁶ kg s⁻¹ m⁻²) reasonably well, making it attractive as next-generation biocompatible piezoelectric devices for health monitoring and “disposable” invasive medical ultrasound imaging.

A small-molecule organic ferroelectric (3,3-DFCBA)Cl has high piezoelectric voltage coefficients g₃₃ (437.2 × 10⁻³ V m N⁻¹), a large electrostriction coefficient Q₃₃, and low acoustic impedance z₀, far beyond that of PZT and PVDF.     

Solvothermal Preparation of a Lanthanide Metal-Organic Framework for Highly Sensitive Discrimination of Nitrofurantoin and l-Tyrosine

Metal-organic frameworks (MOFs) have been rapidly developed for their broad applications in many different chemistry and materials fields. In this work, a multi-dentate building block 5-(4-(tetrazol-5-yl)phenyl)-isophthalic acid (H₃L) containing tetrazole and carbolxylate moieties was employed for the synthesis of a two-dimensional (2D) lanthanide MOF [La(HL)(DMF)₂(NO₃)] (DMF = N,N-dimethylformamide) (1) under solvothermal condition. The fluorescent sensing application of 1 was investigated. 1 exhibits high sensitivity recognition for antibiotic nitrofurantoin (K_sv: 3.0 × 10³ M⁻¹ and detection limit: 17.0 μM) and amino acid l-tyrosine (K_sv: 1.4 × 10⁴ M⁻¹ and detection limit: 3.6 μM). This work provides a feasible detection platform of 2D MOFs for highly sensitive discrimination of antibiotics and amino acids.     

Explorations on Thermodynamic and Kinetic Performances of Various Cationic Exchange Durations for Synthetic Clinoptilolite

Various cation–exchanged clinoptilolites (M–CPs, M = Li⁺, Cs⁺, Ca²⁺, Sr²⁺) were prepared, and their exchanged thermodynamic (and kinetic) properties and adsorption performances for CH₄, N₂, and CO₂ were investigated. The results demonstrated that the relative crystallinity of M–CP_S decreased with the increase of exchange times. Their chemisorbed water weight loss gradually increased with the increasing exchange times, except that of Cs–x–CP. The Δ_rGmθ values of exchange process of Li⁺, Cs⁺, Ca²⁺, or Sr² presented the increased trend with the enhanced exchange times, but they decreased as the temperature increased. The negative Δ_rGmθ values and the positive Δ_rHmθ and Δ_rSmθ values suggested that the exchanged procedure belonged to spontaneous, endothermic, and entropy-increasing behaviors; their kinetic performances followed a pseudo–second–order model. However, the calculated E_a values of exchange process showed the increased tendencies with the enhanced exchange times, indicating that the exchange process became more difficult. Finally, the preliminary adsorption results indicated that the maximum adsorption amount at 273 K and 1 bar was 0.51 mmol/g of CH₄ and 0.38 mmol/g of N₂ by (Na, K)–CP, and 2.32 mmol/g of CO₂ by Li–6–CP.     

Characterization of Diastereomeric Equilibria of Pseudotetrahedral Bis[(R or S)‐N‐1‐(Ar)Ethylsalicylaldiminato‐κ2N,O]zinc(II) with Λ/Δ‐Chirality‐At‐Metal Induction

A family of bis[(R or S)‐N‐1‐(Ar)ethylsalicylaldiminato‐κ²N,O]‐Δ/Λ‐zinc(II) {Ar=C₆H₅ (ZnRL¹ or ZnSL¹), p‐CH₃OC₆H₄ (ZnRL² or ZnSL²) and p‐ClC₆H₄ (ZnRL³ or ZnSL³)} compounds was synthesized and investigated by multiple methods. They feature Λ/Δ‐chirality‐at‐metal induction along the pseudo‐C ₂ axis of the molecules. The chirality induction is quantitative in the solid state, explored by X‐ray crystallography and powder X‐ray diffraction (PXRD), where R or S‐ligated complexes diastereoselectively yield Λ or Δ‐configuration at the metal. On the other hand, Λ and Δ‐diastereomers co‐exist in solution. The Λ⇆Δ equilibrium is solvent‐ and temperature‐dependent. Electronic circular dichroism (ECD) spectra confirm the existence of a diastereomeric excess of Λ‐ZnRL¹⁻³ or Δ‐ZnSL¹⁻³ in solution. DSC analysis reveals thermally induced irreversible phase transformation from a crystalline solid to an isotropic liquid phase. ECD spectra were reproduced by DFT geometry optimizations and time‐dependent DFT (TD‐DFT) calculations, providing ultimate proof of the dominant chirality atmetal in solution.     

Tetra-2,3-Pyrazinoporphyrazines with Externally Appended Pyridine Rings 22 Synthesis,Physicochemical and Photoactivity Studies on In(III) Mono- and Heteropentanuclear Complexes

The basic macrocyclic octapyridinotetrapyrazinoporphyrazine In^III complex of formula [Py₈TPyzPzIn(OAc)]·8H₂O, prepared by reaction of the free ligand [Py₈TPyzPzH₂]·2H₂O with In(OAc)₃, is a stable-to-air species of which the structure has been studied by its X-ray powder diffraction and mass spectra and characterization operated by IR and UV-visible spectral behavior. The complex has been further examined and proven to be of potential interest for its response as an anticancer agent in the field of photodynamic therapy (PDT), the value of Φ_Δ = 0.55 (in DMF) being in the range of 0.4–0.6 at the level of similar phthalocyanine and porphyrazine analogs and qualifying the species as a highly efficient anticancer agent. Planned parallel types of investigation, including their photoactive behaviour in PDT, have been extended to the mononuclear octacation [(2-Mepy)₈TPyzPzIn(OAc)]⁸⁺ (salted by iodide ions) and the heteropentanuclear derivatives [(M’Cl₂)₄Py₈TPyzPzIn(OAc)]·xH₂O (M’ = Pd^II, x = 8; Pt^II, x = 1)) and [{(Pd(CBT)₂)₄}Py₈TPyzPzIn(OAc)]·19H₂O (CBT = m-carborane-1-thiolate anion).     

3D Metal–Organic Frameworks Based on Co(II) and Bithiophendicarboxylate: Synthesis,Crystal Structures,Gas Adsorption,and Magnetic Properties

Three new 3D metal-organic porous frameworks based on Co(II) and 2,2′-bithiophen-5,5′-dicarboxylate (btdc²⁻) [Co₃(btdc)₃(bpy)₂]·4DMF, 1; [Co₃(btdc)₃(pz)(dmf)₂]·4DMF·1.5H₂O, 2; [Co₃(btdc)₃(dmf)₄]∙2DMF∙2H₂O, 3 (bpy = 2,2′-bipyridyl, pz = pyrazine, dmf = N,N-dimethylformamide) were synthesized and structurally characterized. All compounds share the same trinuclear carboxylate building units {Co₃(RCOO)₆}, connected either by btdc^2– ligands (1, 3) or by both btdc^2– and pz bridging ligands (2). The permanent porosity of 1 was confirmed by N₂, O₂, CO, CO₂, CH₄ adsorption measurements at various temperatures (77 K, 273 K, 298 K), resulted in BET surface area 667 m²⋅g⁻¹ and promising gas separation performance with selectivity factors up to 35.7 for CO₂/N₂, 45.4 for CO₂/O₂, 20.8 for CO₂/CO, and 4.8 for CO₂/CH₄. The molar magnetic susceptibilities χ_p(T) were measured for 1 and 2 in the temperature range 1.77–330 K at magnetic fields up to 10 kOe. The room-temperature values of the effective magnetic moments for compounds 1 and 2 are μ_eff (300 K) ≈ 4.93 μ_B. The obtained results confirm the mainly paramagnetic nature of both compounds with some antiferromagnetic interactions at low-temperatures T < 20 K in 2 between the Co(II) cations separated by short pz linkers. Similar conclusions were also derived from the field-depending magnetization data of 1 and 2.     

Bis[pyrrolyl Ru(ii)] triads: a new class of photosensitizers for metal–organic photodynamic therapy

A new family of ten dinuclear Ru(ii) complexes based on the bis[pyrrolyl Ru(ii)] triad scaffold, where two Ru(bpy)₂ centers are separated by a variety of organic linkers, was prepared to evaluate the influence of the organic chromophore on the spectroscopic and in vitro photodynamic therapy (PDT) properties of the compounds. The bis[pyrrolyl Ru(ii)] triads absorbed strongly throughout the visible region, with several members having molar extinction coefficients (ε) ≥ 10⁴ at 600–620 nm and longer. Phosphorescence quantum yields (Φ_p) were generally less than 0.1% and in some cases undetectable. The singlet oxygen quantum yields (Φ_Δ) ranged from 5% to 77% and generally correlated with their photocytotoxicities toward human leukemia (HL-60) cells regardless of the wavelength of light used. Dark cytotoxicities varied ten-fold, with EC₅₀ values in the range of 10–100 μM and phototherapeutic indices (PIs) as large as 5400 and 260 with broadband visible (28 J cm^–2, 7.8 mW cm^–2) and 625 nm red (100 J cm^–2, 42 mW cm^–2) light, respectively. The bis[pyrrolyl Ru(ii)] triad with a pyrenyl linker (5h) was especially potent, with an EC₅₀ value of 1 nM and PI > 27 000 with visible light and subnanomolar activity with 625 nm light (100 J cm^–2, 28 mW cm^–2). The lead compound 5h was also tested in a tumor spheroid assay using the HL60 cell line and exhibited greater photocytotoxicity in this more resistant model (EC₅₀ = 60 nM and PI > 1200 with 625 nm light) despite a lower dark cytotoxicity. The in vitro PDT effects of 5h extended to bacteria, where submicromolar EC₅₀ values and PIs >300 against S. mutans and S. aureus were obtained with visible light. This activity was attenuated with 625 nm red light, but PIs were still near 50. The ligand-localized ³ππ* state contributed by the pyrenyl linker of 5h likely plays a key role in its phototoxic effects toward cancer cells and bacteria.     

Cooperative B–H bond activation: dual site borane activation by redox active κ2-N,S-chelated complexes

Cooperative dual site activation of boranes by redox-active 1,3-N,S-chelated ruthenium species, mer-[PR₃{κ²-N,S-(L)}₂Ru{κ¹-S-(L)}], (mer-2a: R = Cy, mer-2b: R = Ph; L = NC₇H₄S₂), generated from the aerial oxidation of borate complexes, [PR₃{κ²-N,S-(L)}Ru{κ³-H,S,S′-BH₂(L)₂}] (trans–mer-1a: R = Cy, trans–mer-1b: R = Ph; L = NC₇H₄S₂), has been investigated. Utilizing the rich electronic behaviour of these 1,3-N,S-chelated ruthenium species, we have established that a combination of redox-active ligands and metal–ligand cooperativity has a big influence on the multisite borane activation. For example, treatment of mer-2a–b with BH₃·THF led to the isolation of fac-[PR₃Ru{κ³-H,S,S′-(NH₂BSBH₂N)(S₂C₇H₄)₂}] (fac-3a: R = Cy and fac-3b: R = Ph) that captured boranes at both sites of the κ²-N,S-chelated ruthenacycles. The core structure of fac-3a and fac-3b consists of two five-membered ruthenacycles [RuBNCS] which are fused by one butterfly moiety [RuB₂S]. Analogous fac-3c, [PPh₃Ru{κ³-H,S,S′-(NH₂BSBH₂N)(SC₅H₄)₂}], can also be synthesized from the reaction of BH₃·THF with [PPh₃{κ²-N,S-(SNC₅H₄)}{κ³-H,S,S′-BH₂(SNH₄C₅)₂}Ru], cis–fac-1c. In stark contrast, when mer-2b was treated with BH₂Mes (Mes = 2,4,6-trimethyl phenyl) it led to the formation of trans- and cis-bis(dihydroborate) complexes [{κ³-S,H,H-(NH₂BMes)Ru(S₂C₇H₄)}₂], (trans-4 and cis-4). Both the complexes have two five-membered [Ru–(H)₂–B–NCS] ruthenacycles with κ²-H–H coordination modes. Density functional theory (DFT) calculations suggest that the activation of boranes across the dual Ru–N site is more facile than the Ru–S one.

Redox-active ruthenium complexes supported by hemilabile κ²-N,S-chelated ruthenacycles undergo unusual dual site B–H bond activation through metal–ligand cooperation with free and bulky boranes.     

A bis(silylene)pyridine pincer ligand can stabilize mononuclear manganese(0) complexes: facile access to isolable analogues of the elusive d7-Mn(CO)5 radical

Using the potentially tridentate N,N′-bis(N-heterocyclic silylene)pyridine [SiNSi] pincer-type ligand, 2,6-N,N′-diethyl-bis[N,N′-di-tert-butyl(phenylamidinato)silylene] diaminopyridine, led to the first isolable bis(silylene)pyridine-stabilized manganese(0) complex, {κ³-[SiNSi]Mn(dmpe)} 4 (dmpe = (Me₂P)₂C₂H₄), which represents an isolobal 17 VE analogue of the elusive Mn(CO)₅ radical. The compound is accessible through the reductive dehalogenation of the corresponding dihalido (SiNSi)Mn(ii) complexes 1 (Cl) and 2 (Br) with potassium graphite. Exposing 4 towards the stronger π-acceptor ligands CO and 2,6-dimethylphenyl isocyanide afforded the related Mn(0) complexes κ²-[SiNSi]Mn(CO)₃ (5) and κ³-[SiNSi]Mn(CNXylyl)₂(κ¹-dmpe) (6), respectively. Remarkably, the stabilization of Mn(0) in the coordination sphere of the [SiNSi] ligand favors the d⁷ low-spin electronic configuration, as suggested by EPR spectroscopy, SQUID measurements and DFT calculations. The suitability of 4 acting as a superior pre-catalyst in regioselective hydroboration of quinolines has also been demonstrated.

An isolable bis(silylene)pyridine stabilized manganese(0) complex {κ³-[SiNSi]Mn(dmpe)}, isolobal to elusive Mn(CO)₅ radical has been synthesized and fully characterised.     

Dinuclear Lanthanide(III) Complexes from the Use of Methyl 2-Pyridyl Ketoxime: Synthetic,Structural, and Physical Studies

The first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry is described. The 1:2 reactions of Ln(NO₃)₃·nH₂O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln₂(O₂CMe)₄(NO₃)₂(mepaoH)₂] (Ln = Nd, 1; Ln = Eu, 2; Ln = Gd, 3; Ln = Tb, 4; Ln = Dy, 5); the acetato ligands derive from the Ln^III—mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O₂CMe)₃·4H₂O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy₂(O₂CMe)₆(mepaoH)₂] (6). Treatment of 6 with one equivalent of HNO₃ gave 5. The structures of 1, 5, and 6 were solved by single-crystal X-ray crystallography. Elemental analyses and IR spectroscopy provide strong evidence that 2–4 display similar structural characteristics with 1 and 5. The structures of 1–5 consist of dinuclear molecules in which the two Ln^III centers are bridged by two bidentate bridging (η¹:η¹:μ₂) and two chelating-bridging (η¹:η²:μ₂) acetate groups. The Ln^III atoms are each chelated by a N,N’-bidentate mepaoH ligand and a near-symmetrical bidentate nitrato group. The molecular structure of 6 is similar to that of 5, the main difference being the presence of two chelating acetato groups in the former instead of the two chelating nitrato groups in the latter. The geometry of the 9-coordinate Ln^III centers in 1, 5 and 6 can be best described as a muffin-type (MFF-9). The 3D lattices of the isomorphous 1 and 5 are built through H-bonding, π⋯π stacking and C-H⋯π interactions, while the 3D architecture of 6 is stabilized by H bonds. The IR spectra of the complexes are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The Eu(III) complex 2 displays a red, metal-ion centered emission in the solid state; the Tb^III atom in solid 4 emits light in the same region with the ligand. Magnetic susceptibility studies in the 2.0–300 K range reveal weak antiferromagnetic intramolecular Gd^III…Gd^III exchange interactions in 3; the J value is −0.09(1) cm⁻¹ based on the spin Hamiltonian Ĥ = −J(Ŝ_Gd1·Ŝ_Gd2).     

Synthesis and Strong Solvatochromism of Push-Pull Thienylthiazole Boron Complexes

The solvatochromic behavior of two donor-π bridge-acceptor (D-π-A) compounds based on the 2-(3-boryl-2-thienyl)thiazole π-linker and indandione acceptor moiety are investigated. DFT/TD-DFT calculations were performed in combination with steady-state absorption and emission measurements, along with electrochemical studies, to elucidate the effect of two different strongly electron-donating hydrazonyl units on the solvatochromic and fluorescence behavior of these compounds. The Lippert–Mataga equation was used to estimate the change in dipole moments (Δµ) between ground and excited states based on the measured spectroscopic properties in solvents of varying polarity with the data being supported by theoretical studies. The two asymmetrical D-π-A molecules feature strong solvatochromic shifts in fluorescence of up to ~4300 cm⁻¹ and a concomitant change of the emission color from yellow to red. These changes were accompanied by an increase in Stokes shift to reach values as large as ~5700–5800 cm⁻¹. Quantum yields of ca. 0.75 could be observed for the N,N-dimethylhydrazonyl derivative in nonpolar solvents, which gradually decreased along with increasing solvent polarity, as opposed to the consistently reduced values obtained for the N,N-diphenylhydrazonyl derivative of up to ca. 0.20 in nonpolar solvents. These two push–pull molecules are contrasted with a structurally similar acceptor-π bridge-acceptor (A-π-A) compound.     

Involvement of the γ Isoform of cPLA2 in the Biosynthesis of Bioactive N-Acylethanolamines

Arachidonylethanolamide (anandamide) acts as an endogenous ligand of cannabinoid receptors, while other N-acylethanolamines (NAEs), such as palmitylethanolamide and oleylethanolamide, show analgesic, anti-inflammatory, and appetite-suppressing effects through other receptors. In mammalian tissues, NAEs, including anandamide, are produced from glycerophospholipid via N-acyl-phosphatidylethanolamine (NAPE). The ɛ isoform of cytosolic phospholipase A₂ (cPLA₂) functions as an N-acyltransferase to form NAPE. Since the cPLA₂ family consists of six isoforms (α, β, γ, δ, ɛ, and ζ), the present study investigated a possible involvement of isoforms other than ɛ in the NAE biosynthesis. Firstly, when the cells overexpressing one of the cPLA₂ isoforms were labeled with [¹⁴C]ethanolamine, the increase in the production of [¹⁴C]NAPE was observed only with the ɛ-expressing cells. Secondly, when the cells co-expressing ɛ and one of the other isoforms were analyzed, the increase in [¹⁴C]N-acyl-lysophosphatidylethanolamine (lysoNAPE) and [¹⁴C]NAE was seen with the combination of ɛ and γ isoforms. Furthermore, the purified cPLA₂γ hydrolyzed not only NAPE to lysoNAPE, but also lysoNAPE to glycerophospho-N-acylethanolamine (GP-NAE). Thus, the produced GP-NAE was further hydrolyzed to NAE by glycerophosphodiesterase 1. These results suggested that cPLA₂γ is involved in the biosynthesis of NAE by its phospholipase A₁/A₂ and lysophospholipase activities.     

A Cd(II) Luminescent Coordination Grid as a Multiresponsive Fluorescence Sensor for Cr(VI) Oxyanions and Cr(III), Fe(III), and Al(III) in Aqueous Medium

Hydro(solvo)thermal reactions of Cd(NO₃)₂, N-(pyridin-3-ylmethyl)-4-(pyridin-4-yl)-1,8-naphthalimide (NI-mbpy-34), and 5-bromobenzene-1,3-dicarboxylic acid (Br-1,3-H₂bdc) afforded a luminescent coordination polymer, {[Cd(Br-1,3-bdc)(NI-mbpy-34)(H₂O)]∙2H₂O}_n (1). Single-crystal X-ray diffraction analysis showed that 1 features a two-dimensional (2-D) gridlike sql layer with the point symbol of (4⁴·6²), where the Cd(II) center adopts a {CdO₅N₂} pentagonal bipyramidal geometry. Thermogravimetric (TG) analysis confirmed the thermal stability of 1 up to about 340 °C, whereas XRPD patterns proved the maintenance of crystallinity and framework integrity of 1 in CH₂Cl₂, H₂O, CH₃OH, and toluene. Photoluminescence studies indicated that 1 displayed intense blue fluorescence emissions in both solid-state and H₂O suspension-phase. Owing to the good fluorescent properties, 1 could serve as an excellent turn-off fluorescence sensor for selective and sensitive Cr(VI) detection in water, with LOD = 15.15 μM for CrO₄²⁻ and 14.91 μM for Cr₂O₇²⁻, through energy competition absorption mechanism. In addition, 1 could also sensitively detect Cr³⁺, Fe³⁺, and Al³⁺ ions in aqueous medium via fluorescence-enhancement responses, with LOD = 2.81 μM for Cr³⁺, 3.82 μM for Fe³⁺, and 3.37 μM for Al³⁺, mainly through an absorbance-caused enhancement (ACE) mechanism.     

Solid-State Structures and Photoluminescence of Lamellar Architectures of Cu(I) and Ag(I) Paddlewheel Clusters with Hydrogen-Bonded Polar Guests

Two hexanuclear paddlewheel-like clusters appending six carboxylic-acid pendants have been isolated with the inclusion of polar solvent guests: [Cu₆(Hmna)₆]·7DMF (1·7DMF) and [Ag₆(Hmna)₆]·8DMSO (2·8DMSO), where H₂mna = 2-mercaptonicotininc acid, DMF = N,N’-dimethylformamide, and DMSO = dimethyl sulfoxide. The solvated clusters, together with their fully desolvated forms 1 and 2, have been characterized by FTIR, UV–Vis diffuse reflectance spectroscopy, TG-DTA analysis, and DFT calculations. Crystal structures of two solvated clusters 1·7DMF and 2·8DMSO have been unambiguously determined by single-crystal X-ray diffraction analysis. Six carboxylic groups appended on the clusters trap solvent guests, DMF or DMSO, through H-bonds. As a result, alternately stacked lamellar architectures comprising of a paddlewheel cluster layer and H-bonded solvent layer are formed. Upon UV illumination (λ_ex = 365 nm), the solvated hexasilver(I) cluster 2·8DMSO gives intense greenish-yellow photoluminescence in the solid state (λ_PL = 545 nm, Φ_PL = 0.17 at 298 K), whereas the solvated hexacopper(I) cluster 1·7DMF displays PL in the near-IR region (λ_PL = 765 nm, Φ_PL = 0.38 at 298 K). Upon complete desolvation, a substantial bleach in the PL intensity (Φ_PL < 0.01) is observed. The desorption–sorption response was studied by the solid-state PL spectroscopy. Non-covalent interactions in the crystal including intermolecular H-bonds, CH⋯π interactions, and π⋯π stack were found to play decisive roles in the creation of the lamellar architectures, small-molecule trap-and-release behavior, and guest-induced luminescence enhancement.     

Synthesis of a Ni Complex Chelated by a [2.2]Paracyclophane-Functionalized Diimine Ligand and Its Catalytic Activity for Olefin Oligomerization

A diimine ligand having two [2.2]paracyclophanyl substituents at the N atoms (L1) was prepared from the reaction of amino[2.2]paracyclophane with acenaphtenequinone. The ligand reacts with NiBr₂(dme) (dme: 1,2-dimethoxyethane) to form the dibromonickel complex with (R,R) and (S,S) configuration, NiBr₂(L1). The structure of the complex was confirmed by X-ray crystallography. NiBr₂(L1) catalyzes oligomerization of ethylene in the presence of methylaluminoxane (MAO) co-catalyst at 10–50 °C to form a mixture of 1- and 2-butenes after 3 h. The reactions for 6 h and 8 h at 25 °C causes further increase of 2-butene formed via isomerization of 1-butene and formation of hexenes. Reaction of 1-hexene catalyzed by NiBr₂(L1)–MAO produces 2-hexene via isomerization and C12 and C18 hydrocarbons via oligomerization. Consumption of 1-hexene of the reaction obeys first-order kinetics. The kinetic parameters were obtained to be ΔG^‡ = 93.6 kJ mol⁻¹, ΔH^‡ = 63.0 kJ mol⁻¹, and ΔS^‡ = −112 J mol⁻¹deg⁻¹. NiBr₂(L1) catalyzes co-dimerization of ethylene and 1-hexene to form C8 hydrocarbons with higher rate and selectivity than the tetramerization of ethylene.     

Reductive Methylation of Homogeneous Primary β-Lauryl/myristyl 7/3 Polyethyleneoxy n = 3–18 Ethylamines under Phase-Transfer Catalysis Conditions

Homogeneous tertiary N,N-dimethyl-N-β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylamines, LM(EO)_nAT, are niche intermediates in the synthesis of homogeneous N-alkyl (C₁–C₁₈)-N,N-dimethyl-N-β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylammonium chlorides (unitary degree of oligomerization of ethylene oxide in the polyoxyethylene chain). This paper synthetically presents the dependence of the reductive methylation yields of homogeneous primary β-lauryl/myristyl 7/3 polyethyleneoxy n = 3–18 ethylamines, LM(EO)_nAP, on the reaction time (10–90 min), the temperature (70 °C), the molar ratio formic aldehyde /LM(EO)_nAP (1.1/1–2.5/1), the molar ratio HCOOH/LM(EO)_nAP (5/1), the degree of oligomerization of ethylene oxide in the homogeneous polyoxyethylene chain in the 3,6,9,12,18 series, and the structure of the phase-transfer catalysts. The steric effects of hydrophobic groups CH₃ and C₁₈H₃₇ grafted onto the ammonium function, and the micellar phenomena in the vicinity of their critical micellar concentration, directly proportional to the homogeneous degree of oligomerization, were highlighted. In all cases, a steady increase in reductive methylation yields was observed, with even quantitative values obtained. The high purity of the homologous series LM(EO)_nAT will allow their personalization as reference structures for the study of the evolution of basic colloidal characteristics useful in forecasting technological applications. LM(EO)_nAP were obtained either by direct amidoethylation (nucleophilic addition under basic catalysis of homogeneous lauryl/myristyl 7/3 polyethoxylated n = 3, 6, 9, 12, 18 alcohols, LM(EO)_nOH, to acrylamide monomer) or by cyanoethylation of LM(EO)_nOH under basic catalysis at 25–50 °C, in the presence of Fe²⁺ cations as oligomerization/polymerization inhibitor, followed by partial acid hydrolysis of homogeneous β-alkyl (C₁₂H₂₅/C₁₄H₂₉) 7/3 polyethyleneoxy n = 3, 6, 9, 12, 18 propionitriles, LM(EO)_nPN, to β-alkyl (C₁₂H₂₅/C₁₄H₂₉) 7/3 polyethyleneoxy n = 3, 6, 9, 12, 18 propionamides, LM(EO)_nPD, which led to LM(EO)_nAP by Hoffmann degradation. Homogeneous higher tertiary polyetheramines LM(EO)_nAT were structurally characterized.     

Constrained Dipeptide Surrogates: 5- and 7-Hydroxy Indolizidin-2-one Amino Acid Synthesis from Iodolactonization of Dehydro-2,8-diamino Azelates

The constrained dipeptide surrogates 5- and 7-hydroxy indolizidin-2-one N-(Boc)amino acids have been synthesized from L-serine as a chiral educt. A linear precursor ∆⁴-unsaturated (2S,8S)-2,8-bis[N-(Boc)amino]azelic acid was prepared in five steps from L-serine. Although epoxidation and dihydroxylation pathways gave mixtures of hydroxy indolizidin-2-one diastereomers, iodolactonization of the ∆⁴-azelate stereoselectively delivered a lactone iodide from which separable (5S)- and (7S)-hydroxy indolizidin-2-one N-(Boc)amino esters were synthesized by sequences featuring intramolecular iodide displacement and lactam formation. X-ray analysis of the (7S)-hydroxy indolizidin-2-one N-(Boc)amino ester indicated that the backbone dihedral angles embedded in the bicyclic ring system resembled those of the central residues of an ideal type II’ β-turn indicating the potential for peptide mimicry.     

Optimising the Polyphenolic Content and Antioxidant Activity of Green Rooibos (Aspalathus linearis) Using Beta-Cyclodextrin Assisted Extraction

Antioxidant activity associated with green rooibos infusions is attributed to the activity of polyphenols, particularly aspalathin and nothofagin. This study aimed to optimise β-cyclodextrin (β-CD)-assisted extraction of crude green rooibos (CGRE) via total polyphenolic content (TPC) and antioxidant activity assays. Response surface methodology (RSM) permitted optimisation of β-CD concentration (0–15 mM), temperature (40–90 °C) and time (15–60 min). Optimal extraction conditions were: 15 mM β-CD: 40 °C: 60 min with a desirability of 0.985 yielding TPC of 398.25 mg GAE·g⁻¹, metal chelation (MTC) of 93%, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging of 1689.7 µmol TE·g⁻¹, ferric reducing antioxidant power (FRAP) of 2097.53 µmol AAE·g⁻¹ and oxygen radical absorbance capacity (ORAC) of 11,162.82 TE·g⁻¹. Aspalathin, hyperoside and orientin were the major flavonoids, with quercetin, luteolin and chrysoeriol detected in trace quantities. Differences (p < 0.05) between aqueous and β-CD assisted CGRE was only observed for aspalathin reporting the highest content of 172.25 mg·g⁻¹ of dry matter for extracts produced at optimal extraction conditions. Positive, strong correlations between TPC and antioxidant assays were observed and exhibited regression coefficient (R²) between 0.929–0.978 at p < 0.001. These results demonstrated the capacity of β-CD in increasing polyphenol content of green rooibos.