Cooperative redox and spin activity from three redox congeners of sulfur-bridged iron nitrosyl and nickel dithiolene complexes.

The synthesis of sulfur-bridged Fe-Ni heterobimetallics was inspired by Nature's strategies to "trick" abundant first row transition metals into enabling 2-electron processes: redox-active ligands (including pendant iron-sulfur clusters) and proximal metals. Our design to have redox-active ligands on each metal, NO on iron and dithiolene on nickel, resulted in the observation of unexpectedly intricate physical properties. The metallodithiolate, (NO)Fe(N2S2), reacts with a labile ligand derivative of [NiII(S2C2Ph2)]0, NiDT, yielding the expected S-bridged neutral adduct, FeNi, containing a doublet {Fe(NO)}7. Good reversibility of two redox events of FeNi led to isolation of reduced and oxidized congeners. Characterization by various spectroscopies and single-crystal X-ray diffraction concluded that reduction of the FeNi parent yielded [FeNi]-, a rare example of a high-spin {Fe(NO)}8, described as linear FeII(NO-). Mössbauer data is diagnostic for the redox change at the {Fe(NO)}7/8 site. Oxidation of FeNi generated the 2[FeNi]+⇌[Fe2Ni2]2+ equilibrium in solution; crystallization yields only the [Fe2Ni2]2+ dimer, isolated as PF6- and BArF- salts. The monomer is a spin-coupled diradical between {Fe(NO)}7 and NiDT+, while dimerization couples the two NiDT+ via a Ni2S2 rhomb. Magnetic susceptibility studies on the dimer found a singlet ground state with a thermally accessible triplet excited state responsible for the magnetism at 300 K (χMT = 0.67 emu·K·mol-1, µeff = 2.31 µB), and detectable by parallel-mode EPR spectroscopy at 20 to 50 K. A theoretical model built on an H4 chain explains this unexpected low energy triplet state arising from a combination of anti- and ferromagnetic coupling of a four-radical molecular conglomerate.

Photodriven Elimination of Chlorine From Germanium and Platinum in a Dinuclear PtII →GeIV Complex.

Searching for a connection between the two-electron redox behavior of Group-14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o-(Ph2 P)C6 H4 )2 GeIV Cl2 ]PtII Cl2 and [(o-(Ph2 P)C6 H4 )2 ClGeIII ]PtIII Cl3 , two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o-(Ph2 P)C6 H4 )2 ClGeIII ]PtI Cl with quantum yields of 1.7 % and 3.2 % for the GeIV -PtII and GeIII -PtIII isomers, respectively. Conversion of the GeIV -PtII isomer into the platinum germyl complex is a rare example of a light-induced transition-metal/main-group-element bond-forming process. Finally, transient-absorption-spectroscopy studies carried out on the GeIII -PtIII isomer point to a ligand arene-Cl. charge-transfer complex as an intermediate.

Construction of 2D layered TiO2@MoS2heterostructure for efficient adsorption and photodegradation of organic dyes.

In this work, heterostructures of coupled TiO2@MoS2with different phases of MoS2were synthesized via hydrothermal technique. The prepared materials were thoroughly characterized using various techniques, including XRD, SEM, transmission electron microscopy, Brunauer-Emmet-Teller, XPS, Zeta potential and UV-vis spectroscopy. The optimized nanocomposites were tested for the photocatalytic degradation of methyl Orange (MO) under visible light as well as the adsorption of Rhodamine b (RhB) and methelene blue (MB) dyes. The TiO2@1T/2H-MoS2heterostructures exhibited a narrow bandgap compared to the other studied nanomaterials. A remarkable photodegradation efficiency of TiO2@1T/2H-MoS2was observed, which completely degraded 20 ppm of MO after 60 min with high stability over four successive cycles. This can be assigned to the formation of unique heterostructures with aligned energy bands between MoS2nanosheets and TiO2nanobelts. The formation of these novel interfaces promoted the electron transfer and increased the separation efficiency of carriers, resulting in high photocatalytic degradation. Furthermore, the adsorption efficiency of TiO2@1T/2H-MoS2was unique, 20 ppm solutions of RhB and MB were removed after 1 and 2 min, respectively. The superior adsorption performance of the TiO2@1T/2H-MoS2can be attributed to its high surface area (279.9 m2g-1) and the rich concentration of active sites. The kinetics and the isothermal analysis revealed that the TiO2@1T/2H MoS2heterstructures have maximum adsorption capacity of 1200 and 970 mg g-1for RhB and MB, respectively. This study provides a powerful way for designing an effective photocatalyst and adsorbent TiO2-based nanocomposites for water remediation.

Molecular and Electronic Structures and Single-Molecule Magnet Behavior of Tris(thioether)-Iron Complexes Containing Redox-Active α-Diimine Ligands.

Incorporating radical ligands into metal complexes is one of the emerging trends in the design of single-molecule magnets (SMMs). While significant effort has been expended to generate multinuclear transition metal-based SMMs with bridging radical ligands, less attention has been paid to mononuclear transition metal-radical SMMs. Herein, we describe the first α-diiminato radical-containing mononuclear transition metal SMM, namely, [κ2-PhTttBu]Fe(AdNCHCHNAd) (1), and its analogue [κ2-PhTttBu]Fe(CyNCHCHNCy) (2) (PhTttBu = phenyltris(tert-butylthiomethyl)borate, Ad = adamantyl, and Cy = cyclohexyl). 1 and 2 feature nearly identical geometric and electronic structures, as shown by X-ray crystallography and electronic absorption spectroscopy. A more detailed description of the electronic structure of 1 was obtained through EPR and Mössbauer spectroscopies, SQUID magnetometry, and DFT, TD-DFT, and CAS calculations. 1 and 2 are best described as high-spin iron(II) complexes with antiferromagnetically coupled α-diiminato radical ligands. A strong magnetic exchange coupling between the iron(II) ion and the ligand radical was confirmed in 1, with an estimated coupling constant J < -250 cm-1 (J = -657 cm-1, DFT). Calibrated CAS calculations revealed that the ground-state Fe(II)-α-diiminato radical configuration has significant ionic contributions, which are weighted specifically toward the Fe(I)-neutral α-diimine species. Experimental data and theoretical calculations also suggest that 1 possesses an easy-axis anisotropy, with an axial zero-field splitting parameter D in the range from -4 to-1 cm-1. Finally, dynamic magnetic studies show that 1 exhibits slow magnetic relaxation behavior with an energy barrier close to the theoretical maximum, 2|D|. These results demonstrate that incorporating strongly coupled α-diiminato radicals into mononuclear transition metal complexes can be an effective strategy to prepare SMMs.

Magnetostructural and EPR Studies of Anisotropic Vanadium trans-Dicyanide Molecules.

A series of trans-dicyanide vanadium(III) compounds based on acetylacetonate, (PPN)[VIII(acac)2(CN)2]·(PPN)Cl·2MeCN (1), and salen ligands, (Et4N)[VIII(salen)(CN)2] (2a), (PPN)[VIII(MeOsalen)(CN)2]·DMF·2MeCN (3), and (PPN)[VIII(salphen)(CN)2]·DMF (4) [salen = N,N'-ethylenebis(salicyl-imine), MeOsalen = N,N'-ethylenebis(methoxysalicylimine), salphen = N,N'-phenylenebis(salicyl-imine), and PPN = bis(triphenylphosphine)iminium], were prepared and structurally characterized. High-field EPR studies reveal that the complexes exhibit moderate magnetic anisotropy with positive D values of +5.70, +3.80, +4.05, and +3.99 cm-1 for 1-4, respectively.

Slow magnetic relaxation in cobalt N-heterocyclic carbene complexes.

The combined experimental and theoretical investigation of the magnetic properties of the cobalt(ii) NHC complexes (NHC = N-heterocyclic carbene); [Co(CH2SiMe3)2(IPr)] (1), [CoCl2(IMes)2] (2) and [Co(CH3)2(IMes)2] (3) revealed a large easy plane anisotropy for 1 (D = +73.7 cm-1) and a moderate easy axis anisotropy for 2 (D = -7.7 cm-1) due to significant out-of-state spin-orbit coupling. Dynamic magnetic measurements revealed slow relaxation of the magnetization for 1 (Ueff = 22.5 K, τ0 = 3 × 10-7 s, 1000 Oe) and for 2 (Ueff = 20.2 K, τ0 = 1.73 × 10-8 s, 1500 Oe). The molecular origin of the slow relaxation phenomena was further supported by the retention of AC signal in 10% solutions in 2-MeTHF which reveals a second zero field AC signal in 1 at higher frequencies. Compound 3 was found to be an S = 1/2 system.

Geometrical control of the magnetic anisotropy in six coordinate cobalt complexes.

The geometry of cobalt(ii) ions in the axially distorted octahedral cation in [Co(MeCN)6](BF4)2 (1) was compared to the trigonal prismatic cation in [CoTppy]PF6 (2) which revealed significant differences in magnetic anisotropy. Combined experimental and ab initio CASSCF/NEVPT2 calculations support the observed zero field SMM behaviour for 2, with easy axis anisotropy, attributed to the rigidity of the trigonal prismatic ligand. Strong transverse anisotropy for 1 leads to significant quantum tunnelling processes.

A cyanide-bridged wheel featuring a seven-coordinate Mo(iii) center.

A new cyclic molecule incorporating [MoIII(CN)7]4- has been characterized by single crystal X-ray methods, SQUID magnetometry and theoretical calculations. The wheel molecule [MoIII(CN)7]6[Ni(L)]12(H2O)6 exhibits ferromagnetic Mo-Ni coupling which did not exist for the previously reported octacyanometallate analogue [MoIV(CN)8]6[Ni(L)]12(H2O)6. These results indicate that known supramolecular architectures incorporating octacyanometallates can be used as platforms for making new molecules incorporating seven-coordinate cyanide precursors.

Revealing the role of the 1T phase on the adsorption of organic dyes on MoS2 nanosheets.

Herein, different phases of MoS2 nanosheets were synthesized, characterized and tested for dye removal from water. The influence of the MoS2 phases as well as the 1T concentration on the adsorption performance of organic dyes MO, RhB and MB was deeply investigated. The results revealed that the 1T-rich MoS2 nanosheets have superior adsorption performance compared to other 2H and 3R phases. The kinetic results of the adsorption process demonstrate that the experimental data followed the pseudo-second order equation. Meanwhile, the adsorption of dyes over the obtained materials was fitted with several isotherm models. The Langmuir model gives the best fitting to the experimental data with maximum a adsorption capacity of 787 mg g-1. The obtained capacity is significantly higher than that of all previous reports for similar MoS2 materials. Computational studies of the 2H and 1T/2H-MoS2 phases showed that the structural defects present at the 1T/2H grain boundaries enhance the binding of hydroxide and carboxyl groups to the MoS2 surface which in turn increase the adsorption properties of the 1T/2H-MoS2 phase.

A comparative study on the photocatalytic degradation of organic dyes using hybridized 1T/2H, 1T/3R and 2H MoS2 nano-sheets.

MoS2 is a very attractive material and has been well studied for potential applications in various areas. However, due to the wide variety of factors affecting the molecular and electronic structure of MoS2, several contradictory reports about the adsorptive and photocatalytic properties of such materials have been published. In most of these reports, the effect of the actual phase of the materials on the properties was neglected. Here, different phases of MoS2 nanosheets (1T/2H, 1T/3R and 2H) have been obtained using the hydrothermal method with different Mo : S molar ratios and different autoclave filling ratios. The obtained materials have been thoroughly characterized using Raman, UV-vis, powder XRD, SEM, TEM and XPS measurements in order to accurately identify the existing phases in each material. A comparative study of the photocatalytic organic dye degradation efficiency under white light irradiation has been conducted using methyl orange to correlate the different activity of each material to the respective phase composition. The results indicate a much higher performance of the 1T/2H phase compared to the 2H and 3R phases. Detailed computational studies of the different phases revealed the emergence of mid-gap states upon introducing 1T sites into the 2H lattice. This leads to the improvement of the photocatalytic activity of 1T/2H compared to the other prepared materials.

Electronic, Magnetic, and Redox Properties and O2 Reactivity of Iron(II) and Nickel(II) o-Semiquinonate Complexes of a Tris(thioether) Ligand: Uncovering the Intradiol Cleaving Reactivity of an Iron(II) o-Semiquinonate Complex.

The iron(II) semiquinonate character within the iron(III) catecholate species has been proposed by numerous studies to account for the O2 reactivity of intradiol catechol dioxygenases, but a well-characterized iron(II) semiquinonate species that exhibits intradiol cleaving reactivity has not yet been reported. In this study, a detailed electronic structure description of the first iron(II) o-semiquinonate complex, [PhTttBu]Fe(phenSQ) [PhTttBu = phenyltris(tert-butylthiomethyl)borate; phenSQ = 9,10-phenanthrenesemiquinonate; Wang et al. Chem. Commun. 2014, 50, 5871-5873], was generated through a combination of electronic and Mössbauer spectroscopies, SQUID magnetometry, and density functional theory (DFT) calculations. [PhTttBu]Fe(phenSQ) reacts with O2 to generate an intradiol cleavage product, diphenic anhydride, in 16% yield. To assess the dependence of the intradiol reactivity on the identity of the metal ion, the nickel analogue, [PhTttBu]Ni(phenSQ), and its derivative, [PhTttBu]Ni(3,5-DBSQ) (3,5-DBSQ = 3,5-di-tert-butyl-1,2-semiquinonate), were prepared and characterized by X-ray crystallography, mass spectrometry, 1H NMR and electronic spectroscopies, and SQUID magnetometry. DFT calculations, evaluated on the basis of the experimental data, support the electronic structure descriptions of [PhTttBu]Ni(phenSQ) and [PhTttBu]Ni(3,5-DBSQ) as high-spin nickel(II) complexes with antiferromagnetically coupled semiquinonate ligands. Unlike its iron counterpart, [PhTttBu]Ni(phenSQ) decomposes slowly in an O2 atmosphere to generate 14% phenanthrenequinone with a negligible amount of diphenic anhydride. [PhTttBu]Ni(3,5-DBSQ) does not react with O2. This dramatic effect of the metal-ion identity supports the hypothesis that a metal(III) alkylperoxo species serves as an intermediate in the intradiol cleaving reactions. The redox properties of all three complexes were probed using cyclic voltammetry and differential pulse voltammetry, which indicate an inner-sphere electron-transfer mechanism for the formation of phenanthrenequinone. The lack of O2 reactivity of [PhTttBu]Ni(3,5-DBSQ) can be rationalized by the high redox potential of the metal-ligated 3,5-DBSQ/3,5-DBQ couple.

Trigonal antiprismatic Co(ii) single molecule magnets with large uniaxial anisotropies: importance of Raman and tunneling mechanisms.

The air-stable mononuclear Co(ii) compounds [CoII(Tpm)2][ClO4]2 (1, Tpm = tris(pyrazol-1-yl)methane), [CoII(Tpm)2][BPh4]2·2MeCN (2) with trigonal antiprismatic geometry (trigonally elongated octahedral geometry) are reported. Magnetic and theoretical studies reveal that the complexes exhibit single-molecule magnet behavior with uniaxial anisotropy and a huge energy difference between ground and first excited Karmers' doublets (∼200 cm-1). Under applied DC fields, compounds 1 and 2 exhibit frequency and temperature dependence of the imaginary susceptibility. The fit of the data to an Orbach relaxation process yields effective energy barriers of 30.6(1) and 44.7(6) cm-1 for 1 and 2, respectively, but there is no real state at that energy. The inclusion of tunneling, direct and Raman relaxation processes leads to the conclusion that the inclusion of an Orbach process is not required to provide a good fit to the data. More interestingly, a detailed study of the dependence of the relaxation time with field shows that for these Kramers' ions, tunneling is the predominant process at low temperature and that differences in the counteranion allow for a tuning of the Raman process at higher temperatures. These findings underscore the fact that large uniaxial anisotropy can be achieved in hexacoordinate Co(ii) trigonal antiprismatic complexes which is an unexplored geometry in mononuclear single molecule magnets.

A Trigonal-Pyramidal Erbium(III) Single-Molecule Magnet.

Given the recent advent of mononuclear single-molecule magnets (SMMs), a rational approach based on lanthanides with axially elongated f-electron charge cloud (prolate) has only recently received attention. We report herein a new SMM, [Li(THF)4[Er{N(SiMe3)2}3Cl]⋅2 THF, which exhibits slow relaxation of the magnetization under zero dc field with an effective barrier to the reversal of magnetization (ΔEeff/kB =63.3 K) and magnetic hysteresis up to 3 K at a magnetic field sweep rate of 34.6 Oe s(-1). This work questions the theory that oblate or prolate lanthanides must be stabilized with the appropriate ligand framework in order for SMM behavior to be favored.

Ligands effects on the magnetic anisotropy of tetrahedral cobalt complexes.

The effect of ligands with heavy donor atoms on the magnetic anisotropy of the pseudo-tetrahedral cobalt complexes, Co(quinoline)2I2 (1) and Co(EPh3)2I2 (2-3) (E = P, As) has been investigated. The axial zero-field splitting parameter D was found to vary from +9.2 cm(-1) in 1 to -36.9 cm(-1) in 2 and -74.7 cm(-1) in 3. Compounds 2 and 3 exhibit slow relaxation of the magnetization up to 4 K under an applied dc field, indicating SMM behavior.

Magnetic coupling between metal spins through the 7,7,8,8-tetracyanoquinodimethane (TCNQ) dianion.

A family of magnetic metal-organic frameworks, (Ph3PMe)2[M2(TCNQ)3] {M=Fe(2+), Co(2+), Ni(2+) and Zn(2+)} have been prepared and structurally characterized. The honeycomb-like "layers" consist of M(II) ions doubly bridged with dinitrilomethane moieties of two 7,7,8,8-tetracyanoquinodimethane (TCNQ) dianions which are further connected through phenyl rings to form a 3D dianionic framework [M2TCNQ3](2-) with Ph3PMe(+) cations filling cavities that run along the c axis. Studies of the magnetic coupling through the TCNQ dianion in these structures revealed that it can promote long-range magnetic ordering despite the long coupling pathway.

Trigonal bipyramidal 5d-4f molecules with SMM behavior.

A family of trigonal bipyramidal (TBP) 5d-4f cyanide bridged aggregates were synthesized that exhibit slow relaxation of the magnetization below 4 K as indicated by a signal in the out-of-phase ac susceptibility data under zero field.