Theoretical investigation of the electronic structure of Fe(II) complexes at spin-state transitions

The electronic structure relevant to low spin (LS)high spin (HS) transitions in Fe(II) coordination compounds with a FeN6 core are studied. The selected [Fe(tz)6]2+(1) (tz=1H-tetrazole), [Fe(bipy)3]2+(2) (bipy=2,2’-bipyridine) and [Fe(terpy)2]2+ (3) (terpy=2,2’:6’,2’’-terpyridine) complexes have been actively studied experimentally, and with their respective mono-, bi-, and tridentate ligands, they constitute a comprehensive set for theoretical case studies. The methods in this work include density functional theory (DFT), time-dependent DFT (TD-DFT) and multiconfigurational second order perturbation theory (CASPT2). We determine the structural parameters as well as the energy splitting of the LS-HS states (ΔEHL) applying the above methods, and comparing their performance. We also determine the potential energy curves representing the ground and low-energy excited singlet, triplet, and quintet d6 states along the mode(s) that connect the LS and HS states. The results indicate that while DFT is well suited for the prediction of structural parameters, an accurate multiconfigurational approach is essential for the quantitative determination of ΔEHL. In addition, a good qualitative agreement is found between the TD-DFT and CASPT2 potential energy curves. Although the TD-DFT results might differ in some respect (in our case, we found a discrepancy at the triplet states), our results suggest that this approach, with due care, is very promising as an alternative for the very expensive CASPT2 method. Finally, the two dimensional (2D) potential energy surfaces above the plane spanned by the two relevant configuration coordinates in [Fe(terpy)2]2+ were computed both at the DFT and CASPT2 levels. These 2D surfaces indicate that the singlet-triplet and triplet-quintet states are separated along different coordinates, i.e. different vibration modes. Our results confirm that in contrast to the case of complexes with mono- and bidentate ligands, the singlet-quintet transitions in [Fe(terpy)2]2+ cannot be described using a single configuration coordinate

Spin crossover in [MnIII(pyrol)3tren] probed by high-pressure and low-temperature x-ray diffraction

The interplay between the solid-state spin-crossover features and the structural properties is analyzed for the [MnIII(pyrol)3tren] complex on the basis of high-pressure and low-temperature single-crystal x-ray-diffraction experiments. In particular, the low-temperature (30 K, 105 Pa) low spin crystal structure is compared to the low-temperature (60 K, 105 Pa) high spin and to the high-pressure (293 K, 1.00 GPa) high spin crystal structures. The low-temperature structural properties show the structural modifications due to the spin crossover in a Mn(III) complex. Comparison of these structural modifications to those described for mononuclear Fe(II) spin-crossover compounds emphasizes significant differences, such as in bond length variation and polyhedron distortion, for example. Elsewhere, analysis of the high-pressure data shows that the internal stress on the metal ion is not the cause of the occurrence of the thermal spin crossover, contrary to a general belief

Influence of isomerism on recrystallization and cocrystallization induced by CO2 as an antisolvent

Micronization, polymorphism, and cocrystal formation are well-known strategies to modify the characteristics of pharmaceutical ingredients. In this work, recrystallization induced by compressed CO2 as an antisolvent was investigated as a new way to produce aminosalicylate (ASA) polymorphs and cocrystals. Three ASA isomers were first recrystallized as single species. Isomerism has a particular influence on the product characteristics. The 5-ASA isomer was produced as micrometric spherical crystals with improved flow properties but no change in the crystal lattice was observed. 3-ASA recrystallized as micrometric spheres in a less dense crystal packing than that of the raw compound, and the 4-ASA isomer did not exhibit noticeable changes in the morphology or crystal lattice. Cocrystallization of each isomer with nicotinamide resulted in the production of an ASA:NCTA cocrystal only in the case of 4-ASA

Synthesis and Crystal Structure of 3-{4-[(4-(2-Oxo-2,3-dihydro-1H-benzilimidazol-1-yl)piperidin-1-yl)benzyl]}-2-phenylindole

The X-ray crystal structure of 3-{4-[(4-(2-oxo-2,3-dihydro-1H-benzimidazol-1-yl)piperidin-1-yl)benzyl]}-2-phenylindole, a compound that showed high cytotoxic potential against various leukemia cell lines, was established. The 3D spatial determination confirmed the structure in the solid state. It crystallizes inthe triclinic space group P-1 with cell parameters a=9.572(7) Å, b=11.091(2) Å, c=15.976(4) Å, α=92.53(2), β=105.45(3), γ=94.65(3), V=1625.6(13) Å3 and Z=2. The crystal structure was refined to final values of R1=0.0638 and wR2=0.1800. The crystal packing is controlled by intermolecular hydrogen bonding and C-H interactions. In addition, these new data could be further used to clarify the mechanism of action, implicating the antiproliferative effect of this new synthetic indole derivative on human leukemic cells

Comprehensive determination of the solid state stability of Bethanechol Chloride using combined analytical tools

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Syntheses, structural characterisation and magnetic properties of Fe(ii) and Mn(ii) compounds with the pentacyanopropenido ligand; structural characterisation of a substituted pyrazolo[1,5-a]pyrimidine

International audienceReactions between the metal(II) salts [M(CH3CN)n](BF4)2 (M = Fe, n = 6; M = Mn, n = 4) and some organic anionic polynitriles were studied. With the pentacyanopropenide anion pcp− [pcp− = (NC)2CC(CN)C(CN)2−], were obtained, according to the experimental conditions, the new complexes [M(pcp)2(H2O)4] (1, M = Fe; 2, M = Mn) and [M(pcp)2] (3, M = Fe; 4 = Mn). Use of the hexacyano-3,4-diazahexadienediide anion [(NC)2CC(CN)NNC(CN)C(CN)22−] instead of pcp− did not afford polynitrile metal complexes but led to a new organic derivative 5, of formula C10N8H2. Crystallographic studies indicated that the isostructural compounds 1 and 2 involve discrete monomeric units with pcp ligands acting with a monodentate coordination mode and having the metal in a pseudooctahedral trans-MN2O4 environment; however, a rich hydrogen bond system gives rise to a 3D array. Complex 3, which presents metal in a pseudooctahedral MN6 environment, has a 3D structure arising from pcp ligands having an unprecedented μ3-coordination mode. Compound 5 is a bicyclic derivative with a pyrazolo[1,5-a]pyrimidine skeleton. In all derivatives, the organic part is essentially planar and involves a strongly delocalized π system. The magnetic properties of the inorganic complexes have been studied in the 2–300 K range. Fit of the magnetic data indicates high spin complexes with weak antiferromagnetic interactions in 2, 3 and 4 and the presence of a significant zero field splitting of the Fe(II) ion in 1

Synthesis and evaluation of the cytotoxic activity of novel ethyl4-[4-(4-substitutedpiperidin-1-yl)] benzyl-phenylpyrrolo[1,2-alpha] quinoxaline-carboxylate derivatives in myeloid and lymphoid leukemia cell lines

Leukemia is the most common blood cancer, and its development starts at diverse points, leading to distinct subtypes that respond differently to therapy. This heterogeneity is rarely taken into account in therapies, so it is still essential to look for new specific drugs for leukemia subtypes or even for therapyresistant cases. Among heterocyclic compounds that attracted a lot of attention because of its wide spread biological activities, the pyrrolo[1,2-a]quinoxaline heterocyclic framework has been identified as interesting scaffolds for antiproliferative activity against various human cancer cell lines. In the present study, novel ethyl -(4-substitutedpiperidin-1-yl)]benzyl-phenylpyrrolo[1,2-a]quinoxaline-carboxylate derivatives 1a-l have been designed and synthesized. Their cytotoxicities were evaluated against five different leukemia cell lines, including Jurkat and U266 lymphoid cell lines), and K562, U937, HL60 (myeloid cell lines), as well as normal human peripheral blood mononuclear cells (PBMNCs). Then, apoptosis study was performed with the more interesting compounds. The new pyrrolo[1,2-a]quinoxaline series showed promising cytotoxic potential against all leukemia cell lines tested, and some compounds showed better results than the reference compound A6730. Some compounds, such as 1a, 1e, 1g and 1h are promising because of their high activity against leukemia and their low activity against normal hematopoietic cells. Structure-activity relationships of these new synthetic compounds 1a-l are here also discussed