Synthesis of a tetranitrosyl iron complex with unique structure and properties as an inhibitor of phosphodiesterases.

A novel neutral tetranitrosyl iron complex {[Fe(H2O)4]2+[FeR2(NO)2]22-}·4H2O (1) with R = 5-(3-pyridyl)-4H-1,2,4-triazole-3-thiolyls (C7H5N4S), which is a supramolecular ensemble, has been synthesized and studied. As follows from X-ray diffraction analysis, this is an octahedral Fe2+complex (Lewis acid) with two monoanionic dinitrosyl groups [FeR2(NO)2]- (Lewis base) and 4 water molecules as the ligands. As follows from Mössbauer spectra, the coordinating Fe2+ ion is in a low-spin state S = 0, and the dinitrosyl Fe+ ion is in a low-spin state S = 1/2. According to the data of EPR spectroscopy, mass-spectrometry and amperometry, complex 1 in solution forms dinitrosyl particles of [Fe(C7H6N4S-H)2(NO)2]- composition, which are responsible for NO generation. In addition, complex 1 was shown to be a 5-6 times more efficient phosphodiesterase (PDE) inhibitor at 5 × 10-5 M and 10-4 M concentrations than its thioligand. Probable binding sites of the [FeR2(NO)2]- ligand for the bovine PDE1B model have been determined by molecular docking and quantum-chemical calculations.

Formation of supramolecular synthons in the crystalline structure of the dinitrosyl iron complexes with aliphatic thiourea ligands.

By means of quantum-chemical calculations using Density Functional Theory, Quantum Theory of Atoms in Molecules, and Natural Bond Orbitals, theoretical modeling of intermolecular interactions has been performed for eight nitrosyl iron complexes with aliphatic thiourea ligands, which was aimed at discovering the presence of the NO…NO intermolecular interactions and at studying the possibility of the NO…NO supramolecular synthon formation in their crystalline structure for explaining their unusual magnetic properties. Such interactions were shown to be either stacking or T-like interactions, depending on the relative position of nitrosyl ligands and energetically corresponding to Van der Waals bonds. Mainly LP(O), π (NO), and π*(NO) orbitals in various combinations participate in their formation, with π (FeN), π(FeО), and LP(N) orbitals hardly being participants. The involvement of the NO bond orbitals results in quenching the orbital moment of the NO groups. If NO groups are isolated from intermolecular interactions, they can preserve the unquenched orbital moment.

Hydrogenation of 3d-metal oxide clusters: Effects on the structure and magnetic properties.

The geometrical structures and properties of the M8 O12 , M8 O12 H8 , and M8 O12 H12 clusters are explored using density functional theory with the generalized gradient approximation for all 3d-metals M from Sc to Zn. It is found that the geometries and total spin magnetic moments of the clusters depended strongly on the 3d-atom type and the hydrogenation extent. More than the half of all of the 30 clusters had singlet lowest total energy states, which could be described as either nonmagnetic or antiferromagnetic. Hydrogenation increases the total spin magnetic moments of the M8 O12 H12 clusters when MMnNi, which become larger by four Bohr magneton than those of the corresponding unary clusters M8 . Hydrogenation substantially affects such properties as polarizability, forbidden band gaps, and dipole moments. Collective superexchange where the local total spin magnetic moments of two atom squads are coupled antiparallel was observed in antiferromagnetic singlet states of Fe8 O12 H8 and Co8 O12 H8 , whereas the lowest total energy states of their neighbors Mn8 O12 H8 and Ni8 O12 H8 are ferrimagnetic and ferromagnetic, respectively. Hydrogenation leads to a decrease in the average binding energy per atom when moving across the 3d-metal atom series. © 2018 Wiley Periodicals, Inc.

Dependence of Properties and Exchange Coupling Constants on the Charge in the Mn2O n and Fe2O n Series.

The geometrical structure and properties of the neutral and singly charged Mn2O nq and Fe2O nq 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 Mn2O nq and Fe2O nq 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.

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.