Exchange interaction of Mo with 3d and 4d metals in complexes with dithiooxamide: a theoretical modeling

Quantum chemical calculations of the molecular and electronic structure of the complexes [(L)2M13+(L)M22+(L)2]5− (M13+ is the Mo ion in the oxidation state +3; M22+ 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 M13+ and M22+ metal ions in the complexes and in the isolated M13+ and M22+ ions. © 2022, Springer Science+Business Media LLC

Synthesis and structure of 3,4,5-triazidopyridine-2,6-dicarbonitrile possessing the record positive heat of formation

3,4,5-Triazidopyridine-2,6-dicarbonitrile, the first aromatic triazide with three adjacent azido groups in the ring, possessing the record positive heat of formation, was synthesized by azidation of 3,4,5-trichloropyridine-2,6-dicarbonitrile and characterized with X-ray analysis, thermogravimetry, differential scanning calorimetry and spectroscopic methods. © 201

Transitions from stable to metastable states in the Cr2On and Cr2On - series, n = 1-14

The geometrical and electronic structures of the Cr2On and Cr2On - clusters are computed using density functional theory with a generalized gradient approximation in the range of 1 ≤ n ≤ 14. Local total spin magnetic moments, polarizabilities, binding energies per atom, and energies of abstraction of O and O2 are computed for both series along with electron affinities of the neutrals and vertical detachment energies of the anions. In the lowest total energies states of Cr2O2, Cr2O3, Cr2O4, Cr2O14, Cr2O3-, Cr2O4-, and Cr2O14 -, total spin magnetic moments of the Cr atoms are quite large and antiferromagnetically coupled. In the rest of the series, at least one of the Cr atoms has no spin-magnetic moment at all. The computed vertical electron-detachment energies of the Cr2On - are in good agreement with experimental values obtained in the 1 ≤ n ≤ 7 range. All neutral Cr2On possess electron affinities larger than the electron affinities of halogen atoms when n > 6 and are thus superhalogens. It is found that the neutrals and anions are stable with respect to the abstraction of an O atom in the whole range of n considered, whereas both neutrals and anions became unstable toward the loss of O2 for n > 7. The polarizability per atom decreases sharply when n moves from one to four and then remains nearly constant for larger n values in both series. The largest members in both series, Cr2O14 and Cr2O14 -, possess the geometrical structures of the Cr2(O2)7 type by analogy with monochromium Cr(O2)4. © 2017 American Chemical Society

Quantum chemical study of the unusual structure of 3d metal complexes in the gas phase

Based on the previous experimental and theoretical studies of the unusual dome-shaped structures of Pd II and NiII 3,5-di(tert-butyl)-2-oxyazobenzene complexes, gas-phase quantum chemical calculations were performed for related model CuII, CoII, FeII, MnII, CrII, and ZnII 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 FeII, CrII, ZnII and doublet and quartet for CuII, MnII, CoII. 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 CuII-, CoII-, and FeII-based complexes have an unusual dome-shaped structure. © 2021, Springer Science+Business Media LLC

Synthesis and structure of 3,4,5-triazidopyridine-2,6-dicarbonitrile possessing the record positive heat of formation

3,4,5-Triazidopyridine-2,6-dicarbonitrile, the first aromatic triazide with three adjacent azido groups in the ring, possessing the record positive heat of formation, was synthesized by azidation of 3,4,5-trichloropyridine-2,6-dicarbonitrile and characterized with X-ray analysis, thermogravimetry, differential scanning calorimetry and spectroscopic methods. © 201

Intramolecular O -> Te and N -> Te coordination bonds in molecules of beta-tellurocyclohexenals and their nitrogen analogs

The structures of beta-tellurocyclohexenals and their nitrogen analogs, viz., beta-methyl-tellurocyclohexenal (6), beta-(4-ethoxyphenyltelluro)cyclohexenal (7), di(2-formylcyclohexen-1-yl) telluride (8), beta-(4-ethoxyphenyltelluro)cyclohexenylidene(4'-methylaniline) (9), beta-bromotellurenylcyclohexenylidene(4'-methylaniline) (10), and beta-bromotellurenylcyclohexenal (4-methylbenzoyl)hydrazone (11), were studied by X-ray diffraction analysis. Compounds 6-11 have a Z configuration at the double bond, which provides the formation of intramolecular O-->Te or N-->Te coordination bonds. The bonds about the Te atom have a T-shaped configuration. There is only one of two possible O-->Te coordination bonds in dialdehyde 8 and, consequently, this compound belongs to the 10-Te-3-tellurane structural type. Hydrazone 11 possesses both N-->Te and O-->Te intramolecular coordination bonds. Taking into account these interactions, the coordination polyhedron of the tellurium atom can be considered as a trigonal bipyramid. The intramolecular O-->Te or N-->Te coordination bond lengths in compounds 6 (2.692 Angstrom), 7 (2.657 Angstrom), 8 (2.657 Angstrom), and 9 (2.690 Angstrom) are 0.9-1.0 Angstrom smaller than the sums of the van der Waals radii of the corresponding atoms. These bond lengths in compounds 10 (2.170 Angstrom) and 11 (2.203 Angstrom) are almost equal to the standard covalent bond length

Dependence of Properties and Exchange Coupling Constants on the Charge in the Mn2On and Fe2On Series

The geometrical structure and properties of the neutral and singly charged Mn2Onq and Fe2Onq clusters (q = 0, ±1) are computed using density functional theory with the generalized gradient approximation in the range 1 ≤ n ≤ 7. The geometrical structures and spin multiplicities of the corresponding species in all six series are similar except for a few exceptions. Antiferromagnetic coupling of total spin magnetic moments of the metal atoms in the lowest total energy states is observed for the majority of species in all six series when n = 1-5; correspondingly, the computed magnetic exchange coupling constants are mostly negative. The states of Mn2Onq and Fe2Onq are nonmagnetic or weakly ferromagnetic when n > 5 except for Mn2O7+ where the ground state is antiferromagnetic. The computed adiabatic electron affinities and ionization energies of the neutral species in both series are quite close to one another and increase as n increases. However, the binding energies of a single oxygen atom and of an O2 dimer decrease as n increases and the Mn2O7+ and Fe2O7+ cations are barely stable with respect to the O2 abstraction. The most stable and least stable species at a given n are the anions and the cations, respectively. The electric dipole polarizability per atom decreases sharply when n moves from 1 to 4 and then remains nearly constant for larger n values in the anion series, whereas it is close to the asymptotic value already at n = 2 in the neutral series. Copyright © 2018 American Chemical Society