Fibrous TiO2 Alternatives for Semiconductor-Based Catalysts for Photocatalytic Water Remediation Involving Organic Contaminants

Water decontamination remains a challenge in several developed and developing countries. Affordable and efficient approaches are needed urgently. In this scenario, heterogeneous photocatalysts appear as one of the most promising alternatives. This justifies the extensive attention that semiconductors, such as TiO2, have gained over the last decades. Several studies have evaluated their efficiency for environmental applications; however, most of these tests rely on the use of powder materials that have minimal to no applicability for large-scale applications. In this work, we investigated three fibrous TiO2 photocatalysts, TiO2 nanofibers (TNF), TiO2 on glass wool (TGW), and TiO2 in glass fiber filters (TGF). All materials have macroscopic structures that can be easily separated from solutions or that can work as fixed beds under flow conditions. We evaluated and compared their ability to bleach a surrogate dye molecule, crocin, under batch and flow conditions. Using black light (UVA/visible), our catalysts were able to bleach a minimum of 80% of the dye in batch experiments. Under continuous flow experiments, all catalysts could decrease dye absorption under shorter irradiation times: TGF, TNF, and TGW could, respectively, bleach 15, 18, and 43% of the dye with irradiation times as short as 35 s. Catalyst comparison was based on the selection of physical and chemical criteria relevant for application on water remediation. Their relative performance was ranked and applied in a radar plot. The features evaluated here had two distinct groups, chemical performance, which related to the dye degradation, and mechanical properties, which described their applicability in different systems. This comparative analysis gives insights into the selection of the right flow-compatible photocatalyst for water remediation

Tunable Energy-Transfer Process in Heterometallic MOF Materials Based on 2,6-Naphthalenedicarboxylate: Solid-State Lighting and Near-Infrared Luminescence Thermometry

Trivalent lanthanide ions (Ln3+) are used to prepare a plethora of coordination compounds, with metal-organic frameworks (MOFs) being among the most sought-after in recent years. The porosity of Ln-MOFs is often complemented by the luminescence imparted by the metal centers, making them attractive multifunctional materials. Here, we report a class of three-dimensional (3D) MOFs obtained from a solvothermal reaction between 2,6-naphthalenedicarboxylic acid (H2NDC) and lanthanide chlorides, yielding three types of compounds depending on the chosen lanthanide: [LnCl(NDC)(DMF)] for Ln3+ = La3+, Ce3+, Pr3+, Nd3+, Sm3+ (type 1), [Eu(NDC)1.5(DMF)]·0.5DMF (type 2), and [Ln2(NDC)3(DMF)2] for Ln3+ = Tb3+, Dy3+, Y3+, Er3+, Yb3+ (type 3). Photoluminescent properties of selected phases were explored at room temperature. The luminescence thermometry capability of Yb3+-doped Nd-MOF was fully investigated in the 15-300 K temperature range under 365 and 808 nm excitation. To describe the optical behavior of the isolated MOFs, we introduce the total energy-transfer balance model. Therein, the sum of energy-transfer rates is considered along with its dependence on the temperature - the sign, magnitude, and variation of this parameter - permitting to afford a thorough interpretation of the observed behavior of the luminescent species of all materials presented here. The combination of novel theoretical and experimental studies presented herein to describe energy-transfer processes in luminescent materials can pave the way toward the design of MOF-based chemical and physical sensors working in an optical range of interest for biomedical applications.Fil: Gomez, Germán Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Marin, Riccardo. University of Ottawa; CanadáFil: Carneiro Neto, Albano N.. Universidade de Aveiro; PortugalFil: Botas, Alexandre M. P.. Universidade de Aveiro; PortugalFil: Ovens, Jeffrey. University of Ottawa; CanadáFil: Kitos, Alexandros A.. University of Ottawa; CanadáFil: Bernini, Maria Celeste. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Carlos, Luís D.. Universidade de Aveiro; PortugalFil: Soler Illia, Galo Juan de Avila Arturo. Universidad Nacional de San Martin. Instituto de Nanosistemas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Murugesu, Muralee. University of Ottawa; Canad

New members of radical bridged Ln₂ metallocene single-molecule magnets based on the unsubstituted 1,2,4,5-tetrazine ligand

Abstract Magnetic coupling plays a critical role in the overall magnetic behaviour of a single-molecule magnet (SMM). Through a careful design strategy that employs the highly delocalized 1,2,4,5-tetrazinyl (tz) radical anion with lanthanide metallocenes, a new family of dinuclear complexes was isolated; [(Cp*₂LnIII)₂(tz˙−)(THF)₂](BPh₄), (Ln = Gd (1), Tb (2), Dy (3); THF = tetrahydrofuran; Cp* = pentamethylcyclopentadienyl). The strong magnetic exchange coupling of JGd–rad = −7.2 cm−1 observed in 1, was probed through SQUID magnetometry as well as computational studies. This, combined with the highly anisotropic TbIII and DyIII ions in 2 and 3, respectively, leads to zero-field SMM behaviour and slow relaxation of the magnetization through thermally activated processes. These dinuclear complexes serve as ideal models for understanding the magnetic interactions between 4f element

Radical bridged Ln₄ metallocene complexes with strong magnetic coupling and large coercive field

Abstract Inducing magnetic coupling between 4f elements is an ongoing challenge. To overcome this formidable difficulty, we incorporate highly delocalized tetrazinyl radicals, which strongly couple with f-block metallocenes to form discrete tetranuclear complexes. Synthesis, structure, magnetic properties of two tetranuclear [(Cp*₂Ln)₄(tz•)₄]·3(C₆H₆) (Cp* = pentamethylcyclopentadienyl; tz = 1,2,4,5-tetrazine; Ln = Dy, Gd) complexes are reported. An in-depth examination of their magnetic properties through magnetic susceptibility measurements, as well as computational studies, support a highly sought-after radical-induced “giant-spin” model. Strong exchange interactions between the LnIII ions and tz• radicals lead to a strong magnet-like behaviour in this molecular magnet with a giant coercive field of 30 kOe

A new benzodiazepine molecule and its interactions with diorganotin(IV)chlorides

2-Methyl-2,4-di-thiophen-2?,2?-yl-2,3-dihydro-1H-benzo[b][1,4]diazepine (L) has been synthesized through condensation of phenylene-1,2-diamine and 2-acetylthiophene, and its reactions with dialkyltin(IV)dichlorides have been studied. Two salts formulated as (LH)[R2SnCl3] (R = Et, 1; R = Me, 2) have been isolated. L and 1 were structurally characterized. The conformation of the benzodiazepine L, changes in 1 due to H-bonds formation. [Et2SnCl3]- is one of the rare examples of five coordinated tin(IV) species and has distorted trigonal bipyramidal geometry. H-bonding interactions, in 1, lead to the formation of supramolecular helices

Strong magnetic exchange coupling in Ln2 metallocenes attained by the trans-coordination of a tetrazinyl radical ligand

A combination of high-performing lanthanide metallocenes and tetrazine-based radical ligands leads to a new series of radical-bridged dinuclear lanthanide metallocenes; [(Cp*2LnIII)2(bpytz˙−)][BPh4] (where Ln = Gd (1), Tb (2), Dy (3) and Y (4); Cp* = pentamethylcyclopentadienyl; bpytz = 3,6-bis(3,5-dimethyl-pyrazolyl)-1,2,4,5-tetrazine). The formation of the radical species is achieved via a controlled, stepwise synthesis and verified in all complexes by X-ray crystallography and SQUID magnetometry, as well as EPR spectroscopy of 4. Through the judicious choice of the Cp* ancillary ligands and by taking advantage of the steric effects imposed by their bulkiness, we were able to promote the trans coordination mode of the bpytz˙− radical anion that enables stronger magnetic exchange coupling compared to the cis fashion. This yields a JGd–rad = −14.0 cm−1 in 1, which is the strongest exchange coupling observed in organic monoanionic radical-bridged lanthanide metallocene systems. The strong Ln-rad exchange coupling was further confirmed by high-frequency EPR (HF-EPR) spectroscopy and broken-symmetry (BS) density functional theory (DFT) calculations. This combined with the highly anisotropic nature of TbIII and DyIII ions in 2 and 3, respectively, leads to strong SMM behavior and slow relaxation of the magnetization at zero fields.peerReviewe

The search for cobalt single-molecule magnets: A disk-like (CoCo6II)-Co-III cluster with a ligand derived from a novel transformation of 2-acetylpyridine

International audienceThe initial employment of 2-acetylpyridine, (py)(Me)CO, in Co cluster chemistry is reported, and the synthesis, crystal structure, and full magnetic study of [Co-7(OH)(6)(L)(6)](ClO4)(3)center dot 1.6H(2)O (1.1.6H(2)O) are described: L- is the anion of 2-(pyridine-2-yl)pentane-2-ol-4-one, (py)(Me)C(CH2COCH3)(O)(-), formed in situ through a crossed-aldol reaction in acetone under strongly basic conditions. The reaction of Co(ClO4)(2)center dot 6H(2)O, (POMe)CO and (NBu4OMe)-O-II (1:1:1.2) in acetone at room temperature under aerobic conditions affords 1.1.6H(2)O in 35% yield. The mixed-valent cation possesses a wheel-shaped (or disk-like) structural motif comprising a central octahedral Co-III atom linked to six peripheral distorted octahedral Co-II atoms by six mu(3)-OII- groups: the six Co-II atoms on the rim are held together by six eta(1):eta(1):eta(1):mu(2).L- ligands and the oxygen atoms of the hydroxo groups. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on 1. The dc magnetic study of 1 shows a decline in the product chi(T)(M) with decreasing T. The observation of out-of phase (chi ''(M)) ac susceptibility signals below similar to 4 K suggests that the CoIIICo6II complex may be a single molecule magnet, and this was confirmed by single-crystal magnetization vs. dc field sweeps down to 0.04 K that exhibited hysteresis. The study reveals that each complex cation is a weak single-molecule magnet, but that there are also intermolecular interactions (also confirmed crystallographically) to create a 3D ordered lattice: this still gives some hysteresis at 5 K. (C) 2011 Elsevier Ltd. All rights reserved

Linear MnII 3 and cubane Mn II4 carboxylate clusters derived from di-2-pyridyl ketone: Synthesis, characterization and magnetic properties

The employment of di-2-pyridyl ketone, (py) 2CO, in manganese(II) benzoate chemistry is reported. The syntheses, crystal structures and spectroscopic (IR, EPR) characterization are described for [MnII3(O2CPh)6{(py)2CO}2] (1), [MnII3(O2CPh)6{(py)2CO}2]·2MeCN (2·  2MeCN) and [MnII4 (O2CPh)4{(py)2C(OH)O}4] (3), where (py)2C(OH)O- is the monoanion of the gem-diol form of (py)2CO. Variable-temperature, magnetic susceptibility studies on 3 have also been performed. Complexes 1 and 2·2MeCN are linkage isomers. The trinuclear molecules of both complexes have a linear structure, with one η1:η2:μ2 and two syn, syn- η1:η1:μ2 PhCO2- groups spanning each pair of MnII atoms. The terminal MnII atoms are each capped by one κ2 N,N' (py)2CO ligand in orange 1 and one κ2  N,O (py)2CO molecule in the yellow isomer 2·2MeCN. The molecule of 3 has a cubane topology with the MnII centers and the deprotonated oxygen atoms from the η1:η3:η1:μ3 ligands occupying alternate vertices of the cube. A terminal monodentate PhCO2- group completes a distorted octahedral coordination at each MnII atom. The IR data are discussed in terms of the coordination modes of the ligands that are present in the complexes. The Xband EPR spectra of powdered 1 and 2 at 4 K indicate that the populated spin states exhibit a zero-field splitting, while the spectrum of 3 at 18 K is consistent with the presence of magnetically interacting MnII atoms in the solid state. The magnetic properties of 3 in the 300–5 K range have been modelled with two J values, which reveal weak antiferromagnetic interactions within the molecule. Some suggestions have been made concerning the great stability of complex 3

A Systematic Evaluation of the Interplay of Weak and Strong Supramolecular Interactions in a Series of Co(II) and Zn(II) Complexes Tuned by Ligand Modification

A systematic investigation on a designed series of 21 transition metal complexes has been carried out with the intention to explore and assess the relative strength and the way in which intermolecular interactions, namely, weak and strong hydrogen-bonding and π–π interactions, cooperate and direct molecular association during crystallization. The complexes were prepared using the general M^II/X^–/L or HL′ (M^II = Co^II, Zn^II; X^– = Cl^–, Br^–, I^–, NO₃^–, NO₂^–, ClO₄^–; L = 1-methyl-4,5-diphenylimidazole; and HL′ = 4,5-diphenylimidazole) reaction system and were characterized by single-crystal X-ray crystallography. Although the two ligands are structurally similar, the crystal packing organization of their complexes is markedly different. In structures with L, the 3D assembly is based only on weak C–H···X, C–H···π, and intramolecular π···π stacking interactions, whereas in those with HL′, it is the recurring N–H···X motifs that clearly dominate and guide the molecular self-assembly. The formation of such synthons has been activated by choosing appropriate anions X, acting as terminal ligands or counterions. In parallel, the conformational flexibility of the two ligands serves a dual purpose: (i) L contributes to the stabilization of complexes via intramolecular π···π stacking interactions, and (ii) HL′ facilitates the synthon formation by adopting appropriate conformations, even at the expenses of the stabilizing intramolecular π···π stacking