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1.
J Colloid Interface Sci ; 580: 660-668, 2020 Jul 13.
Artigo em Inglês | MEDLINE | ID: mdl-32712472

RESUMO

Layered double hydroxides (LDH) and their magnetic composites have been intensively investigated as recyclable high-capacity phosphate sorbents but with little attention to their stability as function of pH and phosphate concentration. The stability of a Fe3O4@SiO2-Mg3Fe LDH P sorbent as function of pH (5-11) and orthophosphate (Pi) concentration (1-300 mg P/L) was investigated. The composite has high adsorption capacity (approx. 80 mg P/g) at pH 5 but with fast dissolution of the LDH component resulting in formation of ferrihydrite as evidenced by Mössbauer spectroscopy. At pH 7 more than 60% of the LDH dissolves within 60 min, while at alkaline pH, the LDH is more stable but with less than 40% adsorption capacity as compared to pH 5. The high Pi sorption at acid to neutral pH is attributed to Pi bonding to the residual ferrihydrite. Under alkaline conditions Pi is sorbed to LDH at low Pi concentration while magnesium phosphates form at higher Pi concentration evidenced by solid-state 31P MAS NMR, powder X-ray diffraction and chemical analyses. Sorption as function of pH and Pi concentration has been fitted by a Rational 2D function allowing for estimation of Pi sorption and precipitation. In conclusion, the instability of the LDH component limits its application in wastewater treatment from acid to alkaline pH. Future use of magnetic LDH composites requires substantial stabilisation of the LDH component.

2.
Chemistry ; 2020 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-32369645

RESUMO

A homoleptic organometallic Fe(IV) complex that is stable in both solution and in the solid state at ambient conditions has been synthesized and isolated as [Fe(phtmeimb) 2 ](PF 6 ) 2 (phtmeimb = [phenyl(tris(3-methylimidazolin-2-ylidene))borate] - ). This Fe(IV) N -heterocyclic carbene (NHC) complex was characterized by 1 H NMR, HR-MS, elemental analysis, scXRD analysis, electrochemistry, Mößbauer spectroscopy, and magnetic susceptibility. The two latter techniques unequivocally demonstrate that [Fe(phtmeimb) 2 ](PF 6 ) 2 is a triplet Fe(IV) low-spin S =1 complex in the ground state, in agreement with quantum chemical calculations. The electronic absorption spectrum of [Fe(phtmeimb) 2 ](PF 6 ) 2 in acetonitrile shows an intense absorption band in the red and near IR, due to LMCT (ligand-to-metal charge transfer) excitation. For the first time the excited state dynamics of a Fe(IV) complex was studied and revealed a ~0.8 ps lifetime of the 3 LMCT excited state of [Fe(phtmeimb) 2 ](PF 6 ) 2 in acetonitrile.

3.
Inorg Chem ; 2020 Mar 31.
Artigo em Inglês | MEDLINE | ID: mdl-32227864

RESUMO

Presented herein is a first investigation of the chemical reactivity of osmium-nitrido corroles, which are known for their unusual thermal, chemical, and photochemical stability. Elemental chlorine perchlorinates the ß-positions of the triarylcorrole but leaves the OsN unit untouched. The OsN unit is also unaffected by a variety of other electrophilic and nucleophilic reagents. Upon photolysis, however, the anion of Zeise's salt associates with the nitrido ligand to generate an OsVI≡N-PtII complex. The very short OsN-Pt linkage [1.895(9)-1.917(8) Å] and the downfield 195Pt NMR resonance (-2702 ppm) suggest that the OsN corrole acts as a π-accepting ligand toward the Pt(II) center. This finding represents a rare example of the successful photochemical activation of a metal-ligand multiple bond that is too kinetically inert to exhibit any appreciable reactivity under thermal conditions.

4.
Inorg Chem ; 59(1): 235-243, 2020 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-31825607

RESUMO

In this paper, we experimentally study and model the electron donating character of an axial diamagnetic Pd2+ ion in four metalloligated lanthanide complexes of formula [PPh4][Ln{Pd(SAc)4}2] (SAc- = thioacetate, Ln = Tb, Dy, Ho, and Er). A global model encompassing inelastic neutron scattering, torque magnetometry, and dc magnetometry allows to precisely determine the energy level structure of the complexes. Solid state nuclear magnetic resonance reveals a less donating character of Pd2+ compared to the previously reported isostructural Pt2+-based complexes. Consequently, all complexes invariably show a lower crystal field strength compared to their Pt2+-analogues. The dynamic properties show an enhanced single molecule magnet behavior due to the suppression of quantum tunneling, in agreement with our model.

5.
Angew Chem Int Ed Engl ; 58(44): 15650-15654, 2019 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-31290580

RESUMO

The first structurally characterized hexafluorido complex of a tetravalent actinide ion, the [UF6 ]2- anion, is reported in the (NEt4 )2 [UF6 ]⋅2 H2 O salt (1). The weak magnetic response of 1 results from both UIV spin and orbital contributions, as established by combining X-ray magnetic circular dichroism (XMCD) spectroscopy and bulk magnetization measurements. The spin and orbital moments are virtually identical in magnitude, but opposite in sign, resulting in an almost perfect cancellation, which is corroborated by ab initio calculations. This work constitutes the first experimental demonstration of a seemingly non-magnetic molecular actinide complex carrying sizable spin and orbital magnetic moments.

6.
Chem Commun (Camb) ; 55(57): 8270-8273, 2019 Jul 11.
Artigo em Inglês | MEDLINE | ID: mdl-31246199

RESUMO

The sequential treatment of (Cy3P)2Cl2Ru[triple bond, length as m-dash]C with [PtCl2(C2H4)]2 and (dbm)2Cr[triple bond, length as m-dash]N affords trans-(Cy3P)2Cl2Ru[triple bond, length as m-dash]C-PtCl2-N[triple bond, length as m-dash]Cr(dbm)2, in which a platinum(ii) center is coordinated by both carbide and nitride ligands. ESR spectroscopy indicates that the carbide-nitride complex is loosely associated and that its unpaired electron remains localized mainly at the chromium center.

7.
Inorg Chem ; 58(18): 11875-11882, 2019 Sep 16.
Artigo em Inglês | MEDLINE | ID: mdl-31067042

RESUMO

The notion of magnetic anisotropy is very central to the field of molecule-based magnetism, where it is considered to be a key quantity that must be rationalized and controlled in order to improve the performances of, e.g., single-molecule magnets. A rough classification of the magnetic properties is widely done in terms of the qualitative descriptors of magnetic anisotropy: "easy-axis" and "easy-plane". They can be based on different physical properties, in casu: free energy, magnetization, or magnetic susceptibility. However, this degree of freedom leads in some cases, including very simple ones like [V(H2O)6]3+, to incommensurate descriptions of a system being simultaneously easy-axis and easy-plane, depending only on the choice of the physical quantity on which the descriptor is based. Moreover, it has recently been pointed out that the magnetic anisotropy of a chemical system can be addressed and switched using external stimuli like temperature and magnetic field. These external parameters are, though, not the only ones capable of triggering anisotropy switching for actual chemical systems under experimentally relevant conditions. Indeed, this applies also to pressure, as discussed here. In this paper, we try to illustrate the multifaceted nature of magnetic anisotropy and assist the overview using anisotropy phase diagrams.

8.
Inorg Chem ; 58(8): 4812-4819, 2019 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-30916952

RESUMO

We report the first examples of the carbide ligand in (Cy3P)2Cl2Ru≡C (RuC) developing into a µ3 ligand toward metal centers. Conventionally, sterics exclude this coordination mode, but Fe2(CO)9 and Co2(CO)8 expel bridging CO ligands upon reaction with RuC to form trimetallic (Cy3P)2Cl2Ru═CFe2(CO)8 (RuCFe2) and (Cy3P)2Cl2Ru═CCo2(CO)7 (RuCCo2) complexes. Thus, the proximity offered by metal-metal associations in bimetallic carbonyl complexes allows the formation of trinuclear carbide complexes as verified by NMR, Mössbauer, and X-ray spectroscopic techniques.

9.
Science ; 363(6424): 249-253, 2019 01 18.
Artigo em Inglês | MEDLINE | ID: mdl-30498167

RESUMO

Iron's abundance and rich coordination chemistry are potentially appealing features for photochemical applications. However, the photoexcitable charge-transfer states of most iron complexes are limited by picosecond or subpicosecond deactivation through low-lying metal-centered states, resulting in inefficient electron-transfer reactivity and complete lack of photoluminescence. In this study, we show that octahedral coordination of iron(III) by two mono-anionic facial tris-carbene ligands can markedly suppress such deactivation. The resulting complex [Fe(phtmeimb)2]+, where phtmeimb is {phenyl[tris(3-methylimidazol-1-ylidene)]borate}-, exhibits strong, visible, room temperature photoluminescence with a 2.0-nanosecond lifetime and 2% quantum yield via spin-allowed transition from a doublet ligand-to-metal charge-transfer (2LMCT) state to the doublet ground state. Reductive and oxidative electron-transfer reactions were observed for the 2LMCT state of [Fe(phtmeimb)2]+ in bimolecular quenching studies with methylviologen and diphenylamine.

10.
Dalton Trans ; 47(42): 14893-14896, 2018 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-30324186

RESUMO

The reaction of [Ru(CAuCl)Cl2(PCy3)2] with [W([triple bond, length as m-dash]CSnnBu3)(CO)2(Tp*)] (obtained from [W([triple bond, length as m-dash]CBr)(CO)2(Tp*)], nBuLi and ClSnnBu3) affords the heterotetrametallic bis(carbido) complex [WRuAu2(µ-C)2Cl3(CO)2(PCy3)2(Tp*)] in which the two distinct µ-carbido ligands adopt linear and T-shaped geometry at carbon.

11.
Chem Commun (Camb) ; 54(86): 12163-12166, 2018 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-30221297

RESUMO

The recently discovered thermal elasticity of magnetic anisotropy is not at all an exotic phenomenon. For many lanthanide complexes the qualitative nature of their magnetic anisotropy changes as a function of temperature and magnetic field; for some, even multiple times. The theoretically predicted existence of such multi-switch compounds is experimentally corroborated.

12.
Chem Commun (Camb) ; 54(64): 8869-8872, 2018 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-30042991

RESUMO

A new cobalt(ii) complex bearing a pair of cobalt(iii) tris-chelate complexes as metalloligands was prepared. The CoII ion possesses an ideal trigonal antiprismatic geometry because of the intermolecular hydrogen-bonds between the metalloligands via counter anions. This complex exhibits slow magnetic relaxation under a dc field reminiscent of a single-molecule magnet behavior.

13.
Angew Chem Int Ed Engl ; 57(33): 10569-10573, 2018 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-29923289

RESUMO

The tailored chemical synthesis of binary and ternary alloy nanoparticles with a uniform elemental composition is presented. Their dual use as magnetic susceptors for induction heating and catalytic agent for steam reforming of methane to produce hydrogen at temperatures near and above 800 °C is demonstrated. The heating and catalytic performance of two chemically synthesized samples of CoNi and Cu⊂CoNi are compared and held against a traditional Ni-based reforming catalyst. The structural, magnetic, and catalytic properties of the samples were characterized by X-ray diffraction, elemental analysis, magnetometry, and reactivity measurements. For induction-heated catalysts, the conversion rate of methane is limited by chemical reactivity, as opposed to the case of traditional externally heated reformers where heat transport limitations are the limiting factor. Catalyst production by the synthetic route allows controlled doping with miniscule concentrations of auxiliary metals.

14.
Chem Commun (Camb) ; 54(45): 5708-5711, 2018 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-29774335

RESUMO

The sterically accessible carbide complex, (Cy3P)Cl3Ru[triple bond, length as m-dash]C-PtCl(py)2, acts as a synthon for terminal and bridging carbide fragments that relocate to pincer and A-frame scaffolds upon ligand addition. This concept, benefitting from coordination sphere selection as the concluding step, confronts traditional synthetic strategies and broadens the scope for carbide complexes.

15.
Nat Commun ; 9(1): 1292, 2018 03 29.
Artigo em Inglês | MEDLINE | ID: mdl-29599433

RESUMO

Total control over the electronic spin relaxation in molecular nanomagnets is the ultimate goal in the design of new molecules with evermore realizable applications in spin-based devices. For single-ion lanthanide systems, with strong spin-orbit coupling, the potential applications are linked to the energetic structure of the crystal field levels and quantum tunneling within the ground state. Structural engineering of the timescale of these tunneling events via appropriate design of crystal fields represents a fundamental challenge for the synthetic chemist, since tunnel splittings are expected to be suppressed by crystal field environments with sufficiently high-order symmetry. Here, we report the long missing study of the effect of a non-linear (C4) to pseudo-linear (D4d) change in crystal field symmetry in an otherwise chemically unaltered dysprosium complex. From a purely experimental study of crystal field levels and electronic spin dynamics at milliKelvin temperatures, we demonstrate the ensuing threefold reduction of the tunnel splitting.

16.
Chemistry ; 24(20): 5124-5133, 2018 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-29027277

RESUMO

The performance of relativistic density functional theory (DFT) methods has been investigated for the calculation of the recently measured hyperfine coupling constants of hexafluorido complexes [ReF6 ]2- and [IrF6 ]2- . Three relativistic methods were employed at the DFT level of theory: the 2-component zeroth-order regular approximation (ZORA) method, in which the spin-orbit coupling was treated either variationally (EV ZORA) or as a perturbation (LR ZORA), and the 4-component Dirac-Kohn-Sham (DKS) method. The dependence of the results on the basis set and the choice of exchange-correlation functional was studied. Furthermore, the effect of varying the amount of Hartree-Fock exchange in the hybrid functionals was investigated. The LR ZORA and DKS methods combined with DFT led to very similar deviations (about 20 %) from the experimental values for the coupling constant of complex [ReF6 ]2- by using hybrid functionals. However, none of the methods were able to reproduce the large anisotropy of the hyperfine coupling tensor of complex [ReF6 ]2- . For [IrF6 ]2- , the EV ZORA and DKS methods reproduced the experimental tensor components with deviations of ≈10 and ≈5 % for the hybrid functionals, whereas the LR ZORA method predicted the coupling constant to be around one order of magnitude too large owing to the combination of large spin-orbit coupling and very low excitation energies.

17.
J Phys Chem A ; 121(50): 9589-9598, 2017 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-29227102

RESUMO

Two sets of complexes of Co-triarylcorrole-bispyridine complexes, Co[TpXPC](py)2 and Co[Br8TpXPC](py)2 have been synthesized, where TpXPC refers to a meso-tris(para-X-phenyl)corrole ligand with X = CF3, H, Me, and OMe and Br8TpXPC to the corresponding ß-octabrominated ligand. The axial pyridines in these complexes were found to be labile and, in dilute solutions in dichloromethane, the complexes dissociate almost completely to the five-coordinate monopyridine complexes. Upon addition of a small quantity of pyridine, the complexes revert back to the six-coordinate forms. These transformations are accompanied by dramatic changes in color and optical spectra. 1H NMR spectroscopy and X-ray crystallography have confirmed that the bispyridine complexes are authentic low-spin Co(III) species. Strong substituent effects on the Soret maxima and broken-symmetry DFT calculations, however, indicate a CoII-corrole•2- formulation for the five-coordinate Co[TpXPC](py) series. The calculations implicate a Co(dz2)-corrole("a2u") orbital interaction as responsible for the metal-ligand antiferromagnetic coupling that leads to the open-shell singlet ground state of these species. Furthermore, the calculations predict two low-energy S = 1 intermediate-spin Co(III) states, a scenario that we have been able to experimentally corroborate with temperature-dependent EPR studies. Our findings add to the growing body of evidence for noninnocent electronic structures among first-row transition metal corrole derivatives.

18.
Inorg Chem ; 56(20): 12492-12497, 2017 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-28945348

RESUMO

We report the observation of the weakening of the RuC-Pt single bond in (Cy3P)2Cl2Ru≡C-PtCl2-L (Ru≡C-Pt-L) complexes, leading to the incipient formation of the terminal ruthenium carbide complex, (Cy3P)2Cl2Ru≡C (RuC). In the solid state, elongation of RuC-Pt bonds illustrates the degree of weakening, and in solution, decreasing platinum-carbide coupling constants and increasing carbide chemical shifts reveal weaker interaction through the carbide bridge, as the electron donating ability of L becomes progressively stronger. For the bridging carbide ligands, the chemical shifts and coupling constants to platinum are linearly dependent, and NMR data for parent RuC conform to this relationship, providing a spectroscopic means of determining the strength of the RuC-Pt linkages relative to dissociated RuC. The pliancy of the Ru≡C-Pt-L fragment with regard to the identity of L establishes the carbide-bridged complexes as remarkably wide-ranging and sensitive probes for ligand donor abilities.

19.
Chemistry ; 23(47): 11244-11248, 2017 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-28653317

RESUMO

Heavy 5d elements, like osmium, feature strong spin-orbit interactions which are at the origin of exotic physical behaviors. Revealing the full potential of, for example, novel osmium oxide materials ("osmates") is however contingent upon a detailed understanding of the local single-ion properties. Herein, two molecular osmate analogues, [OsF6 ]2- and [OsF6 ]- , are reported as model systems for Os4+ and Os5+ centers found in oxides. Using X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) techniques, combined with state-of-the-art ab initio calculations, their ground state was elucidated; mirroring the osmium electronic structure in osmates. The realization of such molecular model systems provides a unique chemical playground to engineer materials exhibiting spin-orbit entangled phenomena.

20.
Dalton Trans ; 46(18): 6024-6030, 2017 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-28426044

RESUMO

Using a new polydentate Schiff-base ligand (H3L) we isolated three new tetranuclear isostructural lanthanide complexes with the general formula [LnNa2(L)4(DMF)4(H2O)2(AcO)2]·4DMF·2H2O [Ln = Dy (1), Ho (2), or Er (3)]. The structural characterization of the complexes reveals that the Na+ ions are coordinated in the structure which gives them a structure-directing role in the molecule. The magnetic behavior of the systems was investigated by means of SQUID magnetometry which revealed that complex 1 exhibits single molecule magnet behavior at low temperatures which is enhanced by the application of a 2000 Oe static magnetic field. We were able to extract an effective barrier of Ueff = 43(1) K, however, we show that the consideration of an Orbach relaxation mechanism being the dominant is not always correct for lanthanides. On the contrary, we elaborate how in this system the relaxation is caused by a combination of a direct and a Raman process.

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