The paper presents the electron paramagnetic resonance study of defects in the spin chain
o
-
(
DMTTF
)
2
X
family using continuous wave and pulsed techniques. The defects in spin chains are strongly ...correlated and present similar microscopic structure as a molecular magnet. By means of 2D-HYSCORE and DFT calculations, we show a strong reduction of hyperfine coupling between the defects and the nuclear spin bath. We assume that the reduction is due to the Heisenberg exchange interaction which screens the effect of the nuclei.
Deprotonation of 1-arylimidazoles (aryl = mesityl (Mes), 2,6-diisopropylphenyl (Dipp)), with n -butyl lithium afforded the corresponding derivatives (1-aryl-1 H -imidazol-2-yl)lithium ( 1a , Ar = ...Mes; 1b , Ar = Dipp) in good yield. Reaction of 1a with 0.5 equiv. of Ir(cod)(μ-Cl) 2 yielded two geometrical isomers of a doubly C2,N3-bridged dinuclear complex Ir(cod){μ-C 3 H 2 N 2 (Mes)-κC2,κN3} 2 ( 3 ), 3H–H , a head-to-head (H–H) isomer of C S symmetry, and 3H–T , the thermodynamically preferred head-to-tail (H–T) isomer of C 2 symmetry. The metallated carbon of the 4 electron donor anionic bridging ligands has some carbene character, reminiscent of the situation in N-metallated protic NHC complexes. Displacement of cod ligands from 3H–H and 3H–T afforded the tetracarbonyl complexes Ir(CO) 2 {μ-C 3 H 2 N 2 (Mes)-κC2,κN3} 2 4H–H and 4H–T , respectively. The reaction with PMe 3 , which gave only one complex, Ir(CO)(PMe 3 ){μ-C 3 H 2 N 2 (Mes)-κC2,κN3} 2 ( 5 ), demonstrates that the isomerization of the central core Irμ-C 3 H 2 N 2 (Mes)-κC2,κN3 2 Ir from H–H to H–T on going from 4H–H to 5 is readily triggered by phosphine substitution under mild conditions. Oxidative-addition of MeI to 5 afforded the formally metal–metal bonded d 7 –d 7 complex Ir 2 (CO) 2 (PMe 3 ) 2 (Me)I{μ-C 3 H 2 N 2 (Mes)-κC2,κN3} 2 ( 6 ). The blue Ir(C 2 H 4 ) 2 {μ-C 3 H 2 N 2 (Mes)-κC2,κN3} 2 ( 7 ) and purple Rh(C 2 H 4 ) 2 {μ-C 3 H 2 N 2 (Dipp)-κC2,κN3} 2 ( 9 ) tetraethylene complexes were also obtained with only a H–T arrangement of the bridging ligands. Although only modestly efficient in alkane dehydrogenation, complex 7 was found to be a more active pre-catalyst than 3H–T , 4H–T and 5 , probably because of the favorable lability of the ethylene ligands. From cyclic voltammetry, exhaustive coulometry and spectroelectrochemistry studies, it was concluded that 3H–T undergoes a metal-based one electron oxidation to generate the mixed-valent Ir( i )/Ir( ii ) system. The energy of the intervalence band for the orange dirhodium complex Rh(cod){μ-C 3 H 2 N 2 (Mes)-κC2,κN3} 2 ( 8 ) is shifted toward lower energies in comparison with 3H–T , reflecting the decrease of the energy with the intermetallic distance. It was concluded from the EPR study that the Ir and Rh centres contribute substantially to the experimental magnetic anisotropy and thus to the singly occupied molecular orbital (SOMO) in the mixed-valent Ir( i )/Ir( ii ) and Rh( i )/Rh( ii ) systems. The molecular structures of 3H–H , 3H–T , 8 and 9 have been determined by X-ray diffraction.
A tetranuclear copper(II) complex (1) was synthesized using 2‐hydroxy‐N‐(quinolin‐8‐yl)acetamide ligand. Single‐crystal X‐ray diffraction studies revealed that the complex consists of a distorted ...Cu4O4 core in which the four copper(II) ions are linked by alkoxo bridges. X‐ray analysis also evidenced intramolecular noncovalent carbonyl–π interactions. Those interactions that are encountered between lone‐pair electrons (of the amide oxygen atoms here) and π* orbitals of aromatic rings, have been recently recognized as important stabilizing interactions (named n→π*Ar). Computational studies using density functional theory (DFT) were conducted to evaluate the structural role of such interactions in the present tetranuclear entity. The magnetic properties of 1 were also investigated and DFT calculations were employed to predict, rationalize and correlate the exchange interactions operating within this original complex.
A tetranuclear copper(II) complex with a strongly distorted Cu4O4 core was prepared and its magneto‐structural properties are reported. Density functional theory was used to provide a rationale of the magnetic interactions as well as an estimate of the energy of intramolecular n→π* interactions.
We employ electron paramagnetic resonance (EPR) of the spin probe Mn
2+
to study the paraelectric − ferroelectric transition in Dimethylammonium Manganese Formate (DMMnF) and Mn
2+
-doped ...Dimethylammonium Zinc Formate (DMZnF), which are considered model metal − organic frameworks (MOF) with a Pb-free perovskite architecture. In DMMnF, we study the variation of the Mn
2+
EPR line shape and intensity at the X-band (∼9.4 GHz) and over 80 to 300 K, and we show the absence of magnetoelectric coupling at the ferroelectric transition. At the antiferromagnetic transition in DMMnF, we detect a magnetoelectric coupling caused by weak ferromagnetism in the AFM phase. In DMZnF, EPR spectra of the Mn
2+
probe combined with DFT show that the crystal field is predominantly determined by the Dimethylammonium (DMA
+
) cations.
Thiocarbohydrazone-based catalysts feature ligands that are potentially electrochemically active. From the synthesis point of view, these ligands can be easily tailored, opening multiple strategies ...for optimization, such as using different substituent groups or metal substitution. In this work, we show the possibility of a new strategy, involving the nuclearity of the system, meaning the number of metal centers. We report the synthesis and characterization of a trinuclear nickel-thiocarbohydrazone complex displaying an improved turnover rate compared with its mononuclear counterpart. We use DFT calculations to show that the mechanism involved is metal-centered, unlike the metal-assisted ligand-centered mechanism found in the mononuclear complex. Finally, we show that two possible mechanisms can be assigned to this catalyst, both involving an initial double reduction of the system.
Bis(benzimidazole)amine‐based copper complexes, with structural similarities to the active sites of Lytic Polysaccharide Monooxygenase enzymes (LPMOs), were tested for the oxidative degradation of ...cellulose. Spectroscopic characterization of the complexes, as well as structural authentication of one of them, confirm a tetragonal coordination environment with 3 nitrogen donors, as well as a thioether in axial positions. Aqueous oxidative degradation of cellulose was achieved with the CuII complexes and H2O2 as oxidant through putative cupric‐hydroperoxo intermediates. Conversion of cellulose was achieved in up to 67 % yield of soluble oligosaccharide derivatives at ambient temperature and pressure. The products were analyzed in aqueous solution by HPLC‐MS, confirming oxidative depolymerization of cellulose under ambient conditions, in an analogous fashion to LPMOs.
Biomimetic chemistry: LPMO‐inspired benzimidazole‐based copper complexes oxidatively degrade cellulose to cellobiose, aldonic acid and levoglucosan as soluble products in the presence of hydrogen peroxide/triethylamine as oxidant mixture under mild conditions through initially formed cupric hydroperoxo intermediates.
We demonstrate, based on experimental and theoretical evidence, that the isolated 2(CH3CN)22+ complex prepared in CH3CN and containing a mixed‐valent {Cu2II,IS} core evolves towards a new 2(CH3CN)32+ ...species upon solvation in CH3CN. Unlike its type III structural analogue 2(H2O)(OTf)+ active toward N2O reduction, this new type I compound is inactive. This outcome opens new perspectives for a rational for N2O activation using bio‐inspired Cu/S complexes, especially on the role of the valence localization/delocalization and the Cu−Cu bond on the reactivity.
Delocalized or not delocalized? The mixed valent bis‐copper complex 2(CH3CN)22+ was isolated as a powder and has spectroscopic properties of a fully delocalized class III mixed‐valent system. Solvation in acetonitrile results in its total conversion to 2(CH3CN)32+ with this time a fully localized valence (class I). The effect on nitrous oxide reductase (N2Or) activity is discussed.
Two anilinosalen and a mixed phenol‐anilinosalen ligands involving sterically hindered anilines moieties were synthesized. Their nickel(II) complexes 1, 2, and 3 were prepared and characterized. They ...could be readily one‐electron oxidized (E1/2=−0.30, −0.26 and 0.10 V vs. Fc+/Fc, respectively) into anilinyl radicals species 1+, 2+, and 3+, respectively. The radical complexes are extremely stable and were isolated as single crystals. X‐ray crystallographic structures reveal that the changes in bond length resulting from oxidation do not exceed 0.02 Å within the ligand framework in the symmetrical 1+ and 2+. No quinoid bond pattern was present. In contrast, larger structural rearrangements were evidenced for the unsymmetrical 3+, with shortening of one CorthoCmeta bond. Radical species 1+ and 2+ exhibit a strong absorption band at around 6000 cm−1 (class III mixed valence compounds). This band is significantly less intense than 3+, consistent with a rather localized anilinyl radical character, and thus a classification of this species as class II mixed‐valence compound. Magnetic and electronic properties, as well as structural parameters, have been computed by DFT methods.
Nickel(II)‐anilinyl radical complexes from N4‐anilinosalen ligands are remarkably stable; depending on the ligand structure, the radical complexes belong to either class II or class III mixed‐valence compounds (see figure). Solid‐state structure and DFT calculations reveal striking differences between anilinyl and isoelectronic phenoxyl radicals.
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