Formation of a Decanuclear Organometallic Dysprosium Complex via a Radical-Radical Cross-Coupling Reaction.

Over the years, polynuclear cyclic or torus complexes have attracted increasing interest due to their unique metal topologies and properties. However, the isolation of polynuclear cyclic organometallic complexes is extremely challenging due to their inherent reactivity, which stems from the labile and reactive metal-carbon bonds. In this study, the pyrazine ligand undergoes a radical-radical cross-coupling reaction leading to the formation of a decanuclear [(Cp*)20Dy10(L1)10]·12(C7H8) (1; where L1 = anion of 2-prop-2-enyl-2H-pyrazine) complex, where all DyIII metal centers are bridged by the anionic L1 ligand. Amongst the family of polynuclear Ln organometallic complexes bearing CpR2Lnx units, 1 features the highest nuclearity obtained to date. In-depth computational studies were conducted to elucidate the proposed reaction mechanism and formation of L1, while probing of the magnetic properties of 1, revealed slow magnetic relaxation upon application of a static dc field.

Probing the magnetic and magneto-optical properties of a radical-bridged Tb4 single-molecule magnet.

Reaction of the 1,2,4,5-tetrazine (tz˙-) radical and {Cp*2Tb}+ has yielded a tetranuclear radical-bridged TbIII single-molecule magnet. The strong Ln-radical coupling and the electronic differences of the TbIII ions in [(Cp*2Tb)4(tz˙-)4]·3C6H6 (1) are probed via magnetic, magneto-optical and computational studies.

Interesting chemical and physical features of the products of the reactions between trivalent lanthanoids and a tetradentate Schiff base derived from cyclohexane-1,2-diamine.

The initial use of a tetradentate Schiff base (LH2) derived from the 2 : 1 condensation between 2-hydroxyacetophenone and cyclohexane-1,2-diamine in 4f-metal chemistry is described. The 1 : 2 reaction of Ln(NO3)3·xH2O (Ln = lanthanoid or yttrium) and LH2 in MeOH/CH2Cl2 has provided access to isostructural complexes [Ln(NO3)3(L'H2)(MeOH)] in moderate to good yields. Surprisingly, the products contain the corresponding Schiff base ligand L'H2 possessing six aliphatic -CH2- groups instead of the -CH-(CH2)4-CH- unit of the cyclohexane ring, i.e. an unusual ring-opening of the latter has occurred. A mechanism for this LnIII-assisted/promoted LH2 → L'H2 transformation has been proposed assuming transient LnII species and a second LH2 molecule as the H2 source for the reduction of the cyclohexane moiety. DFT calculations provide strong evidence for the great thermodynamic stability of the products in comparison with analogous complexes containing the original intact ligand. The structures of the PrIII, SmIII, GdIII, TbIII, and HoIII complexes have been determined by single-crystal X-ray crystallography. The 9-coordinate LnIII centre in the molecules is bound to six oxygen atoms from the three bidentate chelating nitrato groups, two oxygen atoms that belong to the bidentate chelating organic ligand, and one oxygen atom from the coordinated MeOH group. In the overall neutral bis(zwitterionic) L'H2 ligand, the acidic H atoms are clearly located on the imino nitrogen atoms and this results in the formation of an unusual 16-membered chelating ring. The coordination polyhedra defined by the nine donor atoms around the 4f-metal-ion centres can be best described as distorted, spherical capped square antiprisms. The EuIII, TbIII, and DyIII complexes exhibit LnIII-based luminescence in the visible region, with the coordinated L'H2 molecule acting as the antenna. Ac magnetometry experiments show that the DyIII member of the family behaves as an SIM at zero field and under external dc fields of 0.1 and 0.2 T without the enhancement of the peaks' maxima, suggesting that QTM is not the relaxation path. The GdIII complex behaves, rather unexpectedly, as a SIM with two different magnetic relaxation paths occurring at very close temperatures; this behaviour is tentatively attributed to a very small axial zero-field splitting (D ∼ 0.1 cm-1), which cannot be detected by magnetization or susceptibility experiments. The prospects of the present, first results in the lanthanoid(III)-LH2 chemistry are discussed.

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.

A trivalent 4f complex with two bis-silylamide ligands displaying slow magnetic relaxation.

The best-performing single-molecule magnets (SMMs) have historically relied on pseudoaxial ligands delocalized across several coordinated atoms. This coordination environment has been found to elicit strong magnetic anisotropy, but lanthanide-based SMMs with low coordination numbers have remained synthetically elusive species. Here we report a cationic 4f complex bearing only two bis-silylamide ligands, Yb(III)[{N(SiMePh2)2}2][Al{OC(CF3)3}4], which exhibits slow relaxation of its magnetization. The combination of the bulky silylamide ligands and weakly coordinating [Al{OC(CF3)3}4]- anion provides a sterically hindered environment that suitably stabilizes the pseudotrigonal geometry necessary to elicit strong ground-state magnetic anisotropy. The resolution of the mJ states by luminescence spectroscopy is supported by ab initio calculations, which show a large ground-state splitting of approximately 1,850 cm-1. These results provide a facile route to access a bis-silylamido Yb(III) complex, and further underline the desirability of axially coordinated ligands with well-localized charges for high-performing SMMs.

A cationic fcu-lanthanide MOF enhances the uptake of iodine vapour at room temperature.

The first example of a cationic cluster-based fcu-lanthanide metal-organic framework (MOF) bearing an asymmetric linker, herein named UOTT-4, has been designed and fully characterized. Compared to its rare-earth (RE) anionic counterpart (RE-UiO-66), UOTT-4 was found to significantly improve the performance towards adsorption of iodine vapour at room temperature, opening avenues for the design of the next-generation cationic porous materials for the beneficial uptake and confinement of target molecules.

Expanding the series of alkali metal plumbolyl complexes to Na and K.

Herein we detail the straightforward and scalable synthesis of sodium and potassium complexes of the 2,5-bis(tert-butyldimethylsilyl)-3,4-diphenylplumbolyl dianion (PblTBS,Ph). Their solid-state structures were found to comprise either monomeric solvates or coordination polymers depending on the alkali metal ion and crystallization medium. These complexes were readily prepared with high yields and purity compared to known routes to the dilithium congener of PblTBS,Ph and are well-positioned to serve as convenient precursors for salt metathesis-type reactions leading to metal complexes of the understudied PblTBS,Ph ligand.

Straightforward Mechanosynthesis of a Phase-Pure Interpenetrated MOF-5 Bearing a Size-Matching Tetrazine-Based Linker.

The archetypal metal-organic framework-5 (MOF-5 or IRMOF-1) has been explored as a benchmark sorbent material with untapped potential to be studied in the capture and storage of gases and chemical confinement. Several derivatives of this framework have been prepared using the multivariate (MTV) strategy through mixing size-matching linkers to isolate, for example, MIXMOFs that outperform same-linker congeners when employed as gas reservoirs. Herein, we describe a straightforward protocol that uses mechanosynthesis (solvent-free grinding) followed by mild activation in dimethylformamide (DMF)/CHCl3 (40 °C and ambient pressure) to synthesize a functional phase-pure interpenetrated MOF-5 (int-MOF-5) bearing the size-matching 1,4-benzene dicarboxylate (BDC) and 1,2,4,5-tetrazine-3,6-dicarboxylate (TZDC) linkers in the backbone of the interpenetrated MIXMOF. We found that the grinding involving a mixture of H2TZDC and H2BDC in a 1:4 ratio (20% of H2TZDC) in the presence of zinc(II) acetate yields a crystalline solid that upon activation forms a phase-pure int-MOF-5 herein referred to as 20%TZDC-MOF-5. The crystalline phase, thermal stability, and porous structure of 20%TZDC-MOF-5 were thoroughly characterized, and the gas adsorption performance of the MIXMOF was investigated through the isotherms of N2 and H2 at 77 K and CO2 at 273 and 296 K. The pore size distribution for 20%TZDC-MOF-5 was found to be very similar to that determined using single crystals of the same-linker int-MOF-5. The presence of TZDC in the MIXMOF led to a slight increase in the uptake values for both H2 and CO2, suggesting that beneficial interactions take place. To the best of our knowledge, this is the first report presenting a suitable protocol to yield a functionalized int-MOF-5 as a promising means of synergistically fine-tuning the confinement of small target molecules such as CO2 and H2.

Radical-Bridged Ln4 Metallocene Complexes with Strong Magnetic Coupling and a Large Coercive Field.

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, and magnetic properties of two tetranuclear [(Cp*2 Ln)4 (tz. )4 ]⋅3(C6 H6 ) (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 large coercive field of 30 kOe.

Probing optical and magnetic properties via subtle stereoelectronic effects in mononuclear DyIII-complexes.

Tapping into the secondary coordination environment of mononuclear DyIII-complexes leads to drastic changes in luminescence and magnetism. Visualization of effects induced by stereoelectronics on the opto-magnetic properties was achieved through subtle modifications in the ligand framework.

Lanthanide-Based Molecular Cluster-Aggregates: Optical Barcoding and White-Light Emission with Nanosized {Ln20 } Compounds.

Counterfeit goods represent a major problem to companies, governments, and customers, affecting the global economy. In order to protect the authenticity of products and documents, optical anti-counterfeit technologies have widely been employed via the use of discrete molecular species, extended metal-organic frameworks (MOFs), and nanoparticles. Herein, for the first time we demonstrate the potential use of molecular cluster-aggregates (MCA) as optical barcodes via composition and energy transfer control. The tuneable optical properties for the [Ln20 (chp)30 (CO3 )12 (NO3 )6 (H2 O)6 ], where chp- =deprotonated 6-chloro-2-pyridinol, allow the fine control of the emission colour output, resulting in high-security level optical labelling with a precise read-out. Moreover, a unique tri-doped composition of GdIII , TbIII , and EuIII led to MCAs with white-light emission. The presented methodology is a unique approach to probe the effect of composition control on the luminescent properties of nanosized molecular material.

Enhancing Magnetic Communication between Metal Centres: The Role of s-Tetrazine Based Radicals as Ligands.

Although 1,2,4,5-tetrazines or s-tetrazines have been known in the literature for more than a century, their coordination chemistry has become increasingly popular in recent years due to their unique redox activity, multiple binding sites and their various applications. The electron-poor character of the ring and stabilization of the radical anion through all four nitrogen atoms in their metal complexes provide new aspects in molecular magnetism towards the synthesis of new high performing Single Molecule Magnets (SMMs). The scope of this review is to examine the role of s-tetrazine radical ligands in transition metal and lanthanide based SMMs and provide a critical overview of the progress thus far in this field. As well, general synthetic routes and new insights for the preparation of s-tetrazines are discussed, along with their redox activity and applications in various fields. Concluding remarks along with the limitations and perspectives of these ligands are discussed.

Stark Sublevel-Based Thermometry with Tb(III) and Dy(III) Complexes Cosensitized via the 2-Amidinopyridine Ligand.

Amidine-based ligand frameworks were employed to isolate a series of mononuclear lanthanide complexes. The employed N-2-pyridylimidoyl-2-pyridylamidine (Py2ImAm) undergoes metal-assisted hydrolysis yielding the ligand 2-amidinopyridine (PyAm), which coordinates to the lanthanide ions affording [Ln(acac)3(PyAm)], where Ln = Eu(III) (1), Gd(III) (2), Tb(III) (3), Dy(III) (4) along with the Y(III) analogue (5). The Eu(III), Tb(III), and Dy(III) congeners exhibit characteristic emissions of red, green, and yellow light, respectively, with emission quantum yields of 3, 65, and 8%, respectively. Due to changes in the thermal population of the Stark sublevels, the Tb(III) and Dy(III) complexes can be used as efficient optical thermometers with maximum relative sensitivities of 1.57 and 2.03% K-1 for 3 and 4, respectively. These results demonstrate the viability of PyAm as an antenna for the sensitization of lanthanide ions.

Influence of ligand positional isomerism on the molecular and supramolecular structures of cobalt(II)-phenylimidazole complexes.

In a study to evaluate the impact of flexible positional isomeric ligands on the coordination geometry and self-assembly process of 3d metal complexes, the synthesis of eight new cobalt(II) complexes with the 2-phenylimidazole (LH) and 5-phenylimidazole (L'H) ligands has been carried out. A variety of parameters/conditions have been probed using the general CoII/X-/LH or L'H (X- = Cl-, Br-, I-, NO3-, NCS-, ClO4-, SO42-) reaction system. Interestingly, X-ray analyses reveal two distinct groups of complexes: reactions with LH only lead to tetrahedral or quasi-tetrahedral complexes {i.e. [CoCl2(LH)2] (1), [CoI2(LH)2] (2), [Co(NO3)2(LH)2] (3), [Co(NCS)2(LH)2] (4)}, whereas L'H favours octahedral coordination {i.e. [Co(L'H)4(MeCN)(H2O)]I2 (5), [Co(L'H)4(MeCN)(H2O)](NO3)2 (6) and [Co(NCS)2(L'H)4)]·2MeOH (7·2MeOH)}. A tetrahedral [Co(NCS)2(L'H)2)] (8) complex was also concurrently isolated with complex 7. The effects of the positional isomeric ligands LH and L'H and of the coordinated inorganic anions on the stoichiometry and packing arrangements of the complexes are thoroughly discussed. The supramolecular assembly is firmly directed, in all types of complexes, by robust N-H...X (X = Cl, I, O or S) motifs, leading to varying dimensionalities (1D, 2D or 3D) and packing arrangements. The formation of these motifs has been activated by choosing appropriate anions X, acting as terminal ligands or counterions. At a second level of organization, additional subordinate C-H...X (X = Cl, I, O or S), C-H...π and π...π intermolecular interactions complement the rigidity of the complexes' packing towards compact 3D assemblies. Hirshfeld surface analyses provided insight into the intermolecular interactions, allowed quantification of the individual contact types and comparison between the complexes.

Binding of ligands containing carbonyl and phenol groups to iron(iii): new Fe6, Fe10 and Fe12 coordination clusters.

The initial use of ligands 2'-hydroxyacetophenone (HL1), 2-hydroxybenzophenone (HL2) and 2,2'-dihydroxybenzophenone (H2L3) in iron(iii) chemistry is described. The syntheses and crystal structures are reported for five iron(iii) clusters: [Fe10O4(OMe)14(L1)6(MeOH)2](NO3)2·3MeOH (1·3MeOH), [Fe12O4(OH)(OMe)17(L1)8](ClO4)2·2H2O (2·2H2O), [Fe10O4(OMe)14Cl4(L2)4(MeOH)2] (3), [Fe10O4(OMe)14(L2)6(py)2](ClO4)2·MeOH (4·MeOH), where py = pyridine, and [Fe6O2(OEt)6(O2CMe)2(L3)2(HL3)2] (5). The molecular structures of the decanuclear clusters 1, 3 and 4 are organized around a {Fe10(µ4-O)4(µ3-OMe)2(µ-OMe)12}8+ core consisting of ten {Fe3O4} face-sharing defective cubane units. The core of 2 consists of a {Fe12(µ4-O)4(µ3-OMe)4(µ-OH)(µ-OMe)13}10+ unit composed of twelve {Fe3O4} face-sharing defective cubanes. The ligands (L1)- and (L2)- in 1-4 adopt the O,O'-bidentate chelating coordination mode and their roles are to terminate the further aggregation of the FeIII/O2-/RO- cores. Complex 5 contains the {Fe6(µ4-O)2(µ-OEt)6(µ-Ocarbonyl)2}4+ core, where the µ-Ocarbonyl atoms are the bridging carbonyl oxygens of the two η1:η2:η1:µ (L3)2- ligands; the (HL3)- groups behave as Ophenolate, Ocarbonyl-bidentate chelating ligands with the neutral hydroxyl group being unbound to the FeIII atoms. The core is composed of four {Fe3O4} face-sharing defective cubanes. The FeIII atoms in 1-5 are all six-coordinate with distorted octahedral geometries. The IR spectra of the complexes are discussed in terms of the known coordination modes of the ligands and the ionic character of nitrates and perchlorates. Variable-temperature magnetic susceptibility and variable-field magnetization measurements establish that 2, 3 and 5 have S = 3, 0 and 5 ground states, respectively. The susceptibility data for 5 were fitted using a 3-J model indicating the simultaneous presence of both antiferromagnetic and ferromagnetic FeIIIFeIII exchange interactions. Known magnetostructural correlations in oxido-bridged iron(iii) systems have been applied to rationalise the magnetic behaviour of the three clusters. The results of the present study demonstrate the utility of HL1, HL2 and H2L3 in the stabilisation of robust iron(iii)/oxido/alkoxido clusters.

Interesting copper(ii)-assisted transformations of 2-acetylpyridine and 2-benzoylpyridine.

The reactions of various copper(ii) sources with 2-acetylpyridine, (py)(me)CO, and 2-benzoylpyridine, (py)(ph)CO, under strongly basic conditions have been studied and novel ligand transformations have been discovered. Reaction of Cu(ClO4)2·6H2O and (py)(me)CO in the presence of NBu4(n)OMe (1 : 1 : 1) in CHCl3 gave a mixture of [Cu2Cl2(HLA)2](ClO4)2 (1) and [Cu2Cl2(LB)2(ClO4)2] (2), where HLA is 3-hydroxy-1,3-di(pyridin-2-yl)-butane-1-one and LB is the zwitterionic-type ligand 3-hydroxy-1-methyl-3-(pyridin-2-yl)-3H-indolizin-4-ium. The ligand HLA is formed through an aldol reaction-type mechanism, while the formation of LB takes place via an intramolecular nucleophilic attack of the remote 2-pyridyl nitrogen atom on the positive carbonyl carbon of HLA, after the transformation of the latter through deprotonation and dehydration. The Cu(II) ions in 1 are bridged by two 2.1111 HLA ligands resulting in a long Cu(II)Cu(II) distance (5.338 Å); the metal ions in 2 are triply bridged by the alkoxide oxygen atoms of the two 2.21 LB ligands and one 2.1100 perchlorato group. The absence of α-hydrogens in (py)(ph)CO leads the reactivity of this ligand in the presence of Cu(II) to different pathways. The Cu(ClO4)2·6H2O/(py)(ph)CO/NBu4(n)OMe reaction mixture in MeOH/H2O (25 : 1 v/v) gave the dinuclear cationic complex [Cu2{(py)(ph)CO}2(LC)2](ClO4)2 (3), where LC(-) is the anion of (methoxy)(phenyl)(pyridin-2-yl)methanol formed in situ via the nucleophilic addition of MeO(-) to the carbonyl carbon of (py)(ph)CO upon Cu(II) coordination. The Cu(II) ions in the cation are doubly bridged by the deprotonated oxygen atoms of the two LC(-) ligands. Replacement of Cu(ClO4)2·6H2O with Cu(NO3)2·3H2O and NBu4(n)OMe with NMe4OH and the decrease of the H2O concentration in the above reaction system yielded the tetranuclear coordination cluster [Cu4(OMe)2(NO3)4{(py)(ph)CO}2(LC)2] (4). The Cu(II) centres in this complex define a parallelogram. Two parallel sides of the parallelogram are each supported by deprotonated oxygen atoms belonging to a 2.21 LC(-) ligand and a 2.2 MeO(-) group. The metal ions that define each of the other two sides are singly bridged by an oxygen atom of a 2.210 nitrato group. No bridging exists between the Cu(II) ions that define the two diagonals of the parallelogram. Replacement of MeOH with EtOH in the reaction system that gave 4 resulted in the dinuclear complex [Cu2(NO3)2(LD)2)(EtOH)] (5), LD(-) being the anion of (ethoxy)(phenyl)(pyridin-2-yl)methanol. The Cu(II) ions are doubly bridged by the alkoxide oxygen atoms of the two 2.21 LD(-) ligands. The 1 : 1 : 1 Cu(NO3)2·3H2O/(py)(ph)CO/NMe4OH reaction system in CH3NO2 gave the dinuclear complex [Cu2(NO3)2(LE)2] (6), where LE(-) is the anion of 2-nitro-1-phenyl-1-(pyridin-2-yl)ethanol. The OH(-) ion abstracts one of the methyl hydrogens of CH3NO2, and once the carbanion (-):CH2NO2 is formed it attacks the positive (δ+) carbonyl carbon of (py)(ph)CO; as the carbanion forms the new C-C bond, the π electrons of the carbonyl group of the original ligand are transferred completely to oxygen forming the alkoxide-type ligand LE(-). The Cu(II) ions are doubly bridged by the alkoxide oxygen atoms of the two 2.21 LE(-) ligands. Simplified mechanistic views of the Cu(II)-assisted formation of the transformed ligands are proposed. Dc magnetic susceptibility studies in the 2-300 K range for the representative complexes 3-6 reveal the presence of very strong antiferromagnetic Cu(II)Cu(II) exchange interactions in the dinuclear complexes 3, 5, and 6 and within the dimeric {Cu2(OMe)(NO3){(py)(ph)CO}(LC)}(+) subunits of 4. The strong antiferromagnetic coupling is discussed in terms of the large Cu-O-Cu angles (101.0-102.9°) in the dinuclear, planar {Cu2O2} units/subunits of 3-6.

Rare oxidation-state combinations and unusual structural motifs in hexanuclear Mn complexes using 2-pyridyloximate ligands.

The use of phenyl-2-pyridyl ketone oxime and di-2-pyridyl ketone oxime in Mn chemistry has led to hexanuclear clusters with unprecedented (Mn(II)(4)Mn(III)Mn(IV)) or extremely rare (Mn(II)Mn(III)(5) and Mn(II)(3)Mn(III)(3)) metal oxidation-state combinations and uncommon structural motifs.