Search Results (68)

The integration of mechanics-based analysis and materials design procedures has become central to the development of multi-material structures with tailored mechanical and dynamic performance. In this study, the dynamic and flexural behaviour of multi-material FDM sandwich beams composed of PETG face sheets and an ABS core is experimentally investigated. Seven different infill patterns Grid, Line, Wavy, Honeycomb, Gyroid, Cubic, and Triangle were implemented in the core layer to assess their influence on damping and natural frequency behaviour. Experimental modal analysis was performed using impact testing to identify the first three vibration modes. Natural frequencies were extracted from Frequency Response Functions (FRFs), and modal damping ratios were determined using the half-power bandwidth method. The reliability of the damping results was evaluated through statistical analysis. Additionally, quasi-static three-point bending tests were conducted to assess flexural strength and load-carrying capacity. The results demonstrate that infill topology has a significant impact on both dynamic and mechanical responses. In particular, geometrically complex infill patterns exhibit enhanced stiffness, higher natural frequencies, and improved damping performance. Among the investigated designs, the Triangle infill exhibited the highest natural frequency values across the first three vibration modes (f₁ ≈ 24.910 Hz, f₂ ≈ 162.609 Hz, f ≈ 466.595 Hz), indicating its superior stiffness characteristics. In terms of damping behaviour, the Cubic infill showed the highest loss factor in the first vibration mode (0.0426), while the Line and Gyroid patterns exhibited the highest damping in the second (0.0439) and third modes (0.0354), respectively. Moreover, the force–displacement results revealed that the Triangle infill exhibited the highest load-bearing capacity, further confirming its superior structural stiffness among the investigated designs (SEA = 110.83 J/kg). These findings highlight the potential of multi-material FDM for designing polymer-based sandwich structures with tailored vibration and energy dissipation characteristics. Full article

Density functional theory (DFT) calculations elucidate the mechanism of diastereoselective cyclization of 2-picoline with 1,5-hexadiene catalyzed by a cationic half-sandwich scandium complex. The catalytic cycle proceeds through four key stages: formation of active species, initial alkene insertion, cis-selective cyclization, and protonation. Central to the mechanism is the dual role of 2-picoline, which initially coordinates as a supporting ligand to facilitate C–H activation and regioselective 1,2-insertion but must dissociate to enable stereocontrol. The mono(2-picoline)-coordinated complex C3 is identified as the thermodynamically favored active species. C–H activation reactivity follows the trend: ortho-C(sp²)–H (2-picoline-free) > ortho-C(sp²)–H (2-picoline-coordinated) > benzylic C(sp³)–H (2-picoline-free) > benzylic C(sp³)–H (2-picoline-coordinated), a preference governed by a wider C_α–Sc–C_α′ angle and shorter Sc···X (X = C_α, C_α′, H) distances that enhance scandium–substrate interaction. Subsequent 1,5-hexadiene insertion proceeds with high 1,2-regioselectivity through a picoline-assisted pathway. The stereoselectivity-determining step reveals a mechanistic dichotomy: while picoline coordination is essential for initial activation, its dissociation is required for intramolecular cyclization. This ligand displacement avoids prohibitive steric repulsion in the transition state, directing the reaction exclusively toward the cis-cyclized product. The cycle concludes with a sterically accessible mono-coordinated protonation. This work establishes a “ligand-enabled then ligand-displaced” mechanism, highlighting dynamic substrate coordination as a critical design principle for achieving high selectivity in rare-earth-catalyzed C–H functionalization. Full article

Current tumor diagnostics rely on fluorodeoxyglucose (FDG)-PET imaging, but FDG’s short half-life and high cost limit its widespread use. Infrared (IR) probes are emerging as non-radioactive alternatives to conventional tracers for tissue section and other in vitro imaging applications. Because cells and tissues are relatively free of absorption peaks between 1800 and 2200 cm⁻¹, metal-carbonyl complexes, especially cyclopentadienylrhenium(I) tricarbonyl (Cp[Re(CO)₃]) derivatives, absorb strongly in this window and provide robust platforms for bioconjugation. Furthermore, Cp[Re(CO)₃] fragments can be introduced into organic substrates via an elegant three-component reaction that simultaneously forges the cyclopentadienyl-metal and cyclopentadienyl-substituent bonds. As a result, the functionalized half-sandwich complex is obtained in a single step without any special handling issues. We have therefore properly modified a glucose molecule with that complex and developed a novel glucoconjugated Cp[Re(CO)₃] probe that enables IR-based visualization of diseased cells at 2100 cm⁻¹, offering a non-invasive, non-radioactive histological tool and a promising basis for future medical imaging devices. Full article

The number of structurally investigated cyclopentadienyl (Cp⁻) complexes of technetium is limited in contrast to the situation with its heavier homolog, rhenium. Although this could be attributed to the radioactivity of all isotopes of the radioelement, there are also clear chemical differences to analogous compounds of the other group seven elements, manganese and rhenium. Technetium Cp⁻ compounds are known with the metal in the oxidation states “+1” to “+7”, with a clear dominance of Tc(I) carbonyls and nitrosyls. Corresponding carbonyl complexes also play a significant role in the development of ^99mTc-based radiopharmaceuticals with the aromatic ring as an ideal position for the attachment of biomarkers. In this paper, the present status of the synthetic and structural chemistry of technetium with Cp⁻ ligands is discussed, together with recent developments in the corresponding ^99mTc labeling chemistry. Full article

This study describes a series of water-soluble half-sandwich ruthenium(II), rhodium(III), and iridium(III) complexes with α-diimine ligands containing substituted aromatic groups. These ligands were derived from glyoxal and 2-aminophenol (a), 4-methyl-2-aminophenol (b), 4-aminophenol (c), phenyl hydrazine (d), and 1-aminonaphthalene (e). The ruthenium(II) (1b–1e), rhodium(III) (2a–2c, 2e), and iridium(III) complexes (3a–3e) were obtained by reacting the ligands (a–e) with the corresponding dimeric precursor [(η⁶-p-cym)RuCl₂]₂ (p-cym = p-cymene) or [(η⁵-Cp*)MCl₂]₂ (Cp* = pentamethylcyclopentadienyl, M = Rh, Ir) in air and under nonanhydro conditions. The air-stable and water-soluble ruthenium(II), rhodium(III), and iridium(III) complexes were characterized via nuclear magnetic resonance spectroscopy and electrospray ionization–mass spectrometry. The structures of complexes [(η⁶-p-cym)Ru(d)Cl]Cl, 1d; [(η⁵-Cp*)Ir(a)Cl]Cl, 3a; and [(η⁵-Cp*)Ir(c)Cl]Cl, 3c were determined via single-crystal X-ray diffraction. Additionally, the complexes exhibited catalytic activity as precatalysts in formic acid decomposition. Complex [(η⁵-Cp*)Ir(d)Cl]Cl, 3d achieved turnover number (TON) and turnover frequency (TOF) values of up to 2150 and 3861 h⁻¹, respectively, at short reaction times. In the hydrogenation of carbon dioxide, [(η⁶-p-cym)Ru(e)Cl]Cl, 1e attained TON and TOF values of up to 1385 and 69.25 h⁻¹, respectively. Full article

Polybutadiene (PB) and polyisoprene (PI) rubbers are indispensable synthetic elastomeric materials widely used in tires, footwear, hose, belts, sealants, electricity, construction, and other applications. Nowadays, PB and PI elastomers are produced from butadiene (BD) and isoprene (IP) monomers via transition-metal-mediated coordination polymerization. Transition metal catalytic systems consist of a precise characteristic structural unit at the molecular level: well known as “single-site catalysts” (SSCs). These have experienced a revolutionary advance in the recently developed conjugated dienes synthetic rubber method. Among the SSCs, a class of rare-earth, metal-centered half-sandwich molecule has been identified as a high-performance catalytic system for conjugated dienes polymerization. These novel half-sandwich rare-earth (HSRE) catalytic systems exhibit several irreplaceable advantages compared with the conventional Ziegler–Natta-type catalytic systems. These HSRE catalytic systems can create novel conjugated diene rubbers (CDRs) with high catalytic reactivity, high stereoselectivity, an adjustable polymer chain microstructure, and high molecular weights and are considered to be the next generation of ecofriendly and economic catalytic systems for industrial applications. This paper delivers a concise review of some important synthetic methods for representative HSRE complexes with characteristic structures and of the utilization of some HSRE catalytic systems for the preparation of high-performance CDRs, especially highly stereoregular PI and PB materials. Full article

Towards the efforts to expand the bioactivity and to reduce toxic and adverse properties of known metal-based drugs, various multinuclear complexes have recently been studied. They have shown enhancement of target specificity and selectivity. Different from small organic compounds and traditional metal-based complexes with anticancer activity, iridium(III) multinuclear or heteronuclear metallodrugs have confirmed potential advantages due to their unique biological and chemical diversities, better activity and different anticancer mechanisms. Ir(III) coordination compounds, similar to most Pt group compounds, are of excessive interest because of their potential cytotoxic activity, effective cellular uptake and tolerance by healthy cells. Although mononuclear Ir(III) complex compounds have been extensively studied as promising candidates for antitumor application, the research on the antineoplastic potential of homo- or hetero-multinuclear iridium(III) complexes is not as abundant; nevertheless, intensive investigations have been conducted in the recent years towards developing complexes that are anticipated to have improved therapeutic potential and biotarget selectivity. Multimetallic iridium(III) frameworks have offered interesting possibilities for designing new antitumor agents by exploiting the action of different metal cations at the same time. This method was very successful in the design of homo- and hetero-multinuclear cyclometalated and half-sandwich organometallic Ir(III) compounds. In the described background, many homonuclear and heteronuclear Ir(III) complexes have been estimated and have exposed promising advantages in cancer therapy. This review intends to summarize newly reported innovative and promising multinuclear Ir(III)-based complexes and to afford a wide-ranging overview of current development and perspectives for the practical impact of these complexes in the tumor therapy field. It is anticipated that this analysis will provide significant direction for the further progress of active homonuclear and heteronuclear iridium-based anticancer agents. Full article

The conversion of abandoned butted well salt cavities into underground storage facilities holds immense significance for safeguarding energy security and improving the ecological environment. A significant barrier to the reconstruction of these old cavities is the limited comprehension of their complete morphology, caused by residue coverage. The three-dimensional seismic techniques excel in identifying complex geological structures but have a limited understanding of underground old salt cavity morphology, thus the seismic forward simulation method is utilized to study their seismic response patterns. Based on 3D seismic data, well logging data, and measured cavity shape parameters from the Yexian salt mine region in Henan Province, China, a geological model and observation system were established. The seismic response characteristics of the butted well salt cavern model, encompassing five distinct morphological attributes such as cavity spacing, cavity diameter, cavity height, sediment height, and horizontal connection channel height, were thoroughly investigated. The findings show that the cavity roof exhibits a distinctive “two peaks sandwiching a strong valley” feature, with the positions of the valley and roof remaining aligned and serving as a reliable indicator for identifying the cavity’s top surface. The width of the roof waveform exhibits an exponential amplification effect relative to the cavern width. The residue’s top surface presents an “upward-opening arc” wave peak with a downward shift that diminishes as the residue’s height increases. This peak forms a circular feature with the cavity roof reflection waveform, and the residue’s top surface is always located in the upper half of this circular waveform. The horizontal connection channel’s top and bottom surfaces exhibit contrasting reflection patterns, with the top position aligning with the reflection trough and the bottom reflection waveform shifting downward as the channel height increases. The brine cavern, residue, and bottom of the salt cavern mainly exhibit chaotic reflections. There are distinct identification characteristics on the cavity top, residue top, and connecting channel top in forward simulation. The research findings provide valuable guidance for identifying the morphology of the underground real butted well salt cavity based on 3D seismic data and accelerating the construction of underground energy storage facilities. Full article

Heterobimetallic complexes of an ambidentate deferiprone derivative, 3-hydroxy-2-methyl-1-(3-((pyridin-2-ylmethyl)amino)propyl)pyridin-4(1H)-one (PyPropHpH), incorporating an octahedral [Co(4N)]³⁺ (4N = tris(2-aminoethyl)amine (tren) or tris(2-pyridylmethyl)amine (tpa)) and a half-sandwich type [(η⁶-p-cym)Ru]²⁺ (p-cym = p-cymene) entity have been synthesized and characterized by various analytical techniques. The reaction between PyPropHpH and [Co(4N)Cl]Cl₂ resulted in the exclusive (O,O) coordination of the ligand to Co(III) yielding [Co(tren)PyPropHp](PF₆)₂ (1) and [Co(tpa)PyPropHp](PF₆)₂ (2). This binding mode was further supported by the molecular structure of [Co(tpa)PyPropHp]₂(ClO₄)₃(OH)·6H₂O (5) and [Co(tren)PyPropHpH]Cl(PF₆)₂·2H₂O·C₂H₅OH (6), respectively, obtained via the slow evaporation of the appropriate reaction mixtures and analyzed using X-ray crystallography. Subsequent treatment of 1 or 2 with [Ru(η⁶-p-cym)Cl₂]₂ in a one-pot reaction afforded the corresponding heterobimetallic complexes, [Co(tren)PyPropHp(η⁶-p-cym)RuCl](PF₆)₃ (3) and [Co(tpa)PyPropHp(η⁶-p-cym)RuCl](PF₆)₃ (4), in which the piano-stool Ru core is coordinated by the (N,N) chelating set of the ligand. Cyclic voltammetric measurements revealed that the tpa complexes can be reduced at less negative potentials, suggesting their capability to be bioreductively activated under hypoxia (1% O₂). Hypoxia activation of 2 and 4 was demonstrated by cytotoxicity studies on the MCF-7 human breast cancer cell line. PyPropHpH was shown to be a typical iron-chelating anticancer agent, raising the mRNA levels of TfR1, Ndrg1 and p21. Further qRT-PCR studies provided unambiguous evidence for the bioreduction of 2 after 72 h incubation under hypoxia, in which the characteristic gene induction profile caused by the liberated iron-sequestering PyPropHpH was observed. Full article

The aromatic boron cluster B₈^2– (D_7h) has similar π bonding to C₆H₆, which is named “borozene”. The B₈^2– ligand has been observed to stabilize monovalent Ln(+I) in C_7v-LnB₈⁻ (Ln = La, Pr, Tb, Tm, and Yb) borozene complexes. Low-valency actinide complexes have been reported more rarely, and B₈^2– may be one of the potential ligands. Here, we report a theoretical study on a series of actinide metal-doping octa-boron clusters AnB₈ (An = Pa, U, Np, and Pu). It was found that each species has both half-sandwich and chair-like structures. Except for PaB₈, the half-sandwich structures of UB₈, NpB₈, and PuB₈ are more energetically stable than the chair-like structures, and the half-sandwich clusters of AnB₈ are found to be actinide(II) borozene complexes with the M^II[B₈²⁻] type. For each of the half-sandwich clusters, the B₈²⁻ ligand has σ and π double aromaticity. Various bonding analyses of AnB₈ confirm the covalent interactions between the doped actinide metals and the octa-boron clusters, which further stabilize the complexes and determine the relative stability of AnB₈. As expected, these complexes show high bond dissociation energies, especially PaB₈ with stronger Pa-B covalent bonds. These results demonstrate that the B₈²⁻ doubly aromatic ligand is able to stabilize divalent actinides. Full article

A series of new chelating bidentate (SS) alkylimidazole-2-thione-Ru(II)/Os(II) complexes (3a_i, 3a_ii, 3a_iii, 3b_ii/4a_iii, 4b_i, 4b_ii), and the tridentate (SNS) pyridine-2,6-diylimidazole-2-thione-Ru(II)/Os(II) complexes (5b_i, 5c_iv/6bi, 6c_i, 6c_iv) in the forms [M^II(cym)(L)Cl]PF₆ and [M^II(cym)(L)]PF₆ (M = Ru or Os, cym = η⁶-p-cymene, and L = heterocyclic derivatives of thiourea) respectively, were successfully synthesized. Spectroscopic and analytical methods were used to characterize the complexes and their ligands. Solid-state single-crystal X-ray diffraction analyses revealed a “piano-stool” geometry around the Ru(II) or Os(II) centers in the respective complexes. The complexes were investigated for in vitro chemotherapeutic activities against human cervical carcinoma (HeLa) and the non-cancerous cell line (Hek293) using the MTT assay. The compounds 3a_ii, 5c_iv, 5b_i, 4a_iii, 6c_i, 6c_iv, and the reference drug, 5-fluorouracil were found to be selective toward the tumor cells; the compounds 3a_i, 3a_iii, 3b_ii, 4b_i, 4b_ii, and 6b_i, which were found not to be selective between normal and tumor cell lines. The IC₅₀ value of the tridentate half-sandwich complex 5b_i (86 ± 9 μM) showed comparable anti-proliferative activity with the referenced commercial anti-cancer drug, 5-fluorouracil (87 ± 15 μM). The pincer (SNS) osmium complexes 6c_i (36 ± 10 μM) and 6c_iv (40 ± 4 μM) were twice as effective as the reference drug 5-fluorouracil at the respective dose concentrations. However, the analogous pincer (SNS) ruthenium complex 5c_iv was ineffective and did not show anti-proliferative activity, even at a higher concentration of 147 ± 1 μM. These findings imply that the higher stability of the chelating (SS) and the pincer (SNS) ligand architectures in the complexes improves the biological (anti-proliferative) activity of the complexes by reducing the chance of ligand dissociation under physiological conditions. In general, the pincer (SNS) osmium complexes were found to be more cytotoxic than their ruthenium analogues, suggesting that the anti-proliferative activity of the imidazole-2-thione-Ru/Os complexes depends on the ligand’s spatial coordination, the nature of the metal center, and the charge of the metal complex ions. Full article

Valence tautomerism (VT) may occur if a molecule contains two chemically different redox-active units, which differ only slightly in their intrinsic redox potential. Herein, we present three new half-sandwich complexes [(η⁶-arene)Cr(CO)₂L]⁺ with a triarylmethylium substituent appended to the π-coordinated arene and different coligands L (L = CO, P(OPh)₃, PPh₃, 1⁺–3⁺) at the chromium atom. Ligand substitution purposefully lowers the half-wave potential for chromium oxidation and thereby the redox potential difference towards tritylium reduction. For the PPh₃-substituted complex 3⁺, cyclic voltammetry measurements indicate that chromium oxidation and tritylium reduction occur at (almost) the same potential. This renders the diamagnetic Cr(0)-C₆H₄-CAr₂⁺ form 3⁺, and its paramagnetic diradical Cr(I)^+•-C₆H₄-CAr₂^• valence tautomer 3^+•• energetically nearly degenerate. Temperature-dependent IR spectroscopy indeed shows two pairs of carbonyl bands that are assignable to a Cr(0) and a Cr(I) species, coexisting in a T-dependent equilibrium with almost equal quantities for both at −70 °C. The diradical form with one unpaired spin at the trityl unit engages in a monomer ⇌ dimer equilibrium, which was investigated by means of quantitative EPR spectroscopy. The diradical species 1^+••–3^+•• were found to be highly reactive, leading to several identified reaction products, which presumably result from hydrogen atom abstraction via the trityl C atom, e.g., from the solvent. Full article

Half-sandwich iron(II) dihalido complexes of the type [Fe(η⁵-Cp’)X₂]⁻ (Cp’ = C₅H₅ or substituted cyclopentadienyl) which are thermally stable at room temperature are extremely scarce, being limited to congeners containing the bulky C₅H₂-1,2,4-tBu₃ ligand. We extended this to homologues [Fe(η⁵-Cp*)X₂]⁻ (X = Cl, Br, I) containing the particularly popular C₅Me₅ (Cp*) ligand. Corresponding ionic compounds ER₄[Fe(η⁵-Cp*)X₂] are easily accessible from FeX₂, MCp* (M = Li, K) and a suitable halide source R₄EX (E = N, P) in THF. Despite their high sensitivity towards air and moisture, the new compounds NnPr₄[Fe(η⁵-Cp*)X₂] (X = Cl, Br), NnPr₄[Fe(η⁵-Cp*)BrCl], and PPh₄[Fe(η⁵-Cp*)X₂] (X = Cl, Br, I) were structurally characterised using single-crystal X-ray diffraction. NnPr₄[Fe(η⁵-Cp*)Cl₂] reacts readily with CO to afford [Fe(η⁵-Cp*)Cl(CO)₂], indicating the synthetic potential of ER₄[Fe(η⁵-Cp*)X₂] in FeCp* half-sandwich chemistry. Full article