Lithium metal phosphate (Li2MPO4) and silicates (Li2MSiO4) (where M=Fe, Mn, and Co) are promising polyanion cathodes for rechargeable lithium batteries, owing to the inherent merits such as low cost, ...decent electrochemical property, and high stability. However, these merits have often been undermined by insufficient energy and power delivery due to poor Li extraction/insertion kinetics. It is generally believed that the extremely low conductivity, i.e. ∼10−9scm−1 for phosphates and 10−12–10−16scm−1 for silicates at room temperature, in combination with slow Li ion diffusion could account for such sluggish Li cycling kinetics. To address this critical issue, it is essential to integrate well-defined nano-carbons such as one-dimensional (1D) carbon nanotube (CNT), two-dimensional (2D) graphene, and their three-dimensional (3D) assembly into polyanion materials. By constructing hybrid architectures, integrated composites could afford much improved activity towards Li storage versus the bare ones. In this short review, we summarize recent advance in integrating CNT, graphene, and their 3D assemblies into LiMPO4 and Li2MSiO4 cathodes, with particular emphasis on how the cathodes interact with carbon materials and their mechanism. We also conclude some general rules to engineer such integration structures to maximize their utilization towards Li storage.
Quantum chemical calculations of the molecular and electronic structure of the complexes (L)
2
M1
3+
(L)M2
2+
(L)
2
5−
(M1
3+
is the Mo ion in the oxidation state +3; M2
2+
is the 3d and 4d ...transition-metal (Fe, Ru, Rh, Pd) ion in the oxidation state +2; and L is the dithiooxamide ligand) were carried out to search for pairs of metals corresponding to the maximum value of the exchange coupling constant
J
. Molecular structure calculations of the complexes were performed in the B3LYP/LANL2DZ approximation while the
J
constants were obtained from B3LYP/TZV calculations. It was shown that replacement of 3d transition-metal ions in the oxidation state +2 by 4d transition-metal ions in the oxidation state +2 leads to higher
J
values. It was established that the
J
values change in parallel with the difference between the total spin density on the M1
3+
and M2
2+
metal ions in the complexes and in the isolated M1
3+
and M2
2+
ions.
The mechanisms of hydrolysis of a model iron–sulfur–nitrosyl complex (ISNC) Fe(NO)
2
(SCH
2
)
2
+
1
with thioformaldehyde ligands have been studied using the density functional theory and ...polarizable continuum model of water. Quantum chemical calculations employed the TPSSH and M06 functionals and def2-TZVP basis set and took into account interactions with water medium. Hydrolysis of
1
was found to be an exothermic process with small activation energy whereas exchange of NO for H
2
O is thermodynamically unfavorable. The calculations have predicted lower activation barrier for the associative mechanism with concerted replacement of SCH
2
by H
2
O than for dissociative mechanism with homolytic bond cleavage of the Fe–S coordination bond in water. The mechanism of hydrolysis that involves participation of OH
–
was found to be less probable at pH 7. The calculation results show that ISNC
1
is of {Fe
1+
(NO
•
)
2
}
9
type and retains its tetrahedral structure that is typical for crystals of ISNC with thiocarbonyl ligands.
A mechanism of the reaction between the cationic nitrosyl iron complex with thiourea ligands Fe(SC(NH
2
)
2
)
2
(NO)
2
+
Cl
−
and molecular oxygen in aqueous solution is proposed. It was ...demonstrated that NO released as reaction product can undergo subsequent transformations in the presence of molecular oxygen and water. As a result, various oxygen-containing products including NO
2
, NO
2
−
, NO
3
−
, and ONOO
−
are released to the solution. A mechanism was proposed for the formation of an OH radical in the system, which makes it possible to explain the experimental data on the kinetics of NO release by the complex under study under aerobic and anaerobic conditions.
Indoline spiropyran containing an σ-acceptor chlorine atom in 6′ position of the 2
H
-chromene part of the molecule was synthesized and studied. The use of 1,2,3,3-tetramethyl-3
H
-indolium ...perchlorate as a starting compound made it possible to achieve higher product yields as compared to previous studies. The molecular structure of the compound was established by single crystal X-ray diffraction analysis. The features of the crystal structure and intermolecular interactions were investigated using CrystalExplorer17 software package. The photochromic behavior in acetonitrile solution was studied for the first time. It was found that the merocyanine form of spiropyran is characterized by an absorption maximum at 592 nm, which is 37 nm closer to the range of the “biological window” in comparison with the nitro-substituted analog.
The structures of 3,5-di-(
tert
-butyl)-2-hydroxyazobenzene (L) in the free state and in complexes with Ni
2+
(
I
) and Pd
2+
(
II
) cations are studied by X-ray diffraction (XRD). The same space ...group
R
с
with close unit cell parameters, the same crystal structure motif, and unusual conformations of the cupola-shaped coordination polyhedra of complexes
I
and
II
are revealed by XRD for ligand L. In complexes
I
and
II
based on this compound as the ligand, the coordinating atoms form
trans
-planar coordination nodes.
Mechanisms of reactions between cations of mononuclear dinitrosyliron complexes (DNIC) bearing alkyl-substituted thiourea ligands and molecular oxygen were studied by the density functional theory. ...The optimized geometries of the initial, final, intermediate, and transition states were obtained and the energy profiles of the reactions were plotted. It was shown that in some cases the alkyl substituents introduced into the thiourea ligands significantly influence the mechanism of the reaction with molecular oxygen.
Based on the previous experimental and theoretical studies of the unusual dome-shaped structures of Pd
II
and Ni
II
3,5-di(
tert
-butyl)-2-oxyazobenzene complexes, gas-phase quantum chemical ...calculations were performed for related model Cu
II
, Co
II
, Fe
II
, Mn
II
, Cr
II
, and Zn
II
complexes. The calculations were carried out with full geometry optimization at the TPSSh/def2tzvp(Cu,Co,Fe,Mn,Cr,Zn)/6-311G*(C,N,O,H) level of theory. All compounds were calculated in the low-spin and high-spin states — singlet and triplet for Fe
II
, Cr
II
, Zn
II
and doublet and quartet for Cu
II
, Mn
II
, Co
II
. Metal complexes with a closed shell (Zn), a half-filled shell (Cr), and a half-filled d-subshell (Mn) have a tetrahedral structure in the gas-phase ground energy state, whereas Cu
II
-, Co
II
-, and Fe
II
-based complexes have an unusual dome-shaped structure.
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