Four new heterometallic complexes combining M
(H
dapsc)
cations with the chelating H
dapsc {2,6-diacetylpyridine-bis(semicarbazone)} Schiff base ligand and Cr(CN)
anion were synthesized: {M
(H
...dapsc)Cr
(CN)
K(H
O)
(EtOH)
}
·1.2
(H
O), M = Mn (
) and Co (
), {Mn(H
dapsc)
Cr(CN)
(H
O)
}Cl·H
O (
) and {Co(H
dapsc)
Cr(CN)
(H
O)
}Cl·2EtOH·3H
O (
). In all the compounds, M(II) centers are seven-coordinated by N
O
atoms of H
dapsc in the equatorial plane and N or O atoms of two apical -CN/water ligands. Crystals
and
are isostructural and contain infinite negatively charged chains of alternating M
(H
dapsc)
and Cr
(CN)
units linked by CN-bridges. Compounds
and
consist of centrosymmetric positively charged trimers in which two M
(H
dapsc)
cations are bound through one Cr
(CN)
anion. All structures are regulated by π-stacking of coplanar H
dapsc moieties as well as by an extensive net of hydrogen bonding. Adjacent chains in
and
interact also by coordination bonds via a pair of K
ions. The compounds containing Mn
(
,
) and Co
(
,
) show a significant difference in magnetic properties. The ac magnetic measurements revealed that complexes
and
behave as a spin glass and a field-induced single-molecule magnet, respectively, while
and
do not exhibit slow magnetic relaxation in zero and non-zero dc fields. The relationship between magnetic properties and non-covalent interactions in the structures
-
was traced.
ortho-Pyrovanadate (or ortho-diorthovanadate) K2Mn2 3+Mn2+O(OH)(VO4)(V2O7) synthesized hydrothermally crystallizes in the orthorhombic space group Pnma with a = 17.9155(5), b = 5.8940(2), c = ...10.9971(3) Å, V = 1161.23(6) Å3, and Z = 4. Its crystal structure features linear chains of edge-sharing Mn3+O6 octahedra with every second pair of Mn3+O6 octahedra condensed with a Mn2+O6 octahedron on one side of a chain in a sawtooth pattern so that each sawtooth chain consists of a triangular trimer. These sawtooth chains, running parallel to the b axis and linked by the VO4 and V2O7 groups, form a framework with channels populated by K atoms. The new compound is a structural analogue of the mineral zoisite Ca2Al3O(OH)(SiO4)(Si2O7), showing a striking example of very different chemical compositions. K2Mn3O(OH)(VO4)(V2O7) undergoes a phase transition into an ordered antiferromagnetic (AFM) state at T N = 14.4 K, which was detected by high-frequency electron spin resonance as well as by both specific heat C p and Fisher’s specific heat d(χT)/dT measurements. However, this phase transition was not detected by magnetic susceptibility measurements. The origin of this puzzling observation was resolved by evaluating the spin exchanges of K2Mn3O(OH)(VO4)(V2O7), which revealed that each triangular trimer is a ferromagnetically coupled cluster, and the observed ordering involves an AFM ordering between the ferromagnetic (FM) clusters. This ordering is shrouded in magnetic susceptibility measurements due to the susceptibility contributions from the individual FM triangular trimers even below T N. We showed that the magnetic susceptibility of K2Mn3O(OH)(VO4)(V2O7) between ∼30 K and room temperature is satisfactorily described by an AFM chain made up of ferromagnetically coupled triangular clusters, as described by a few spin-exchange parameters.
Three tetraphenylborates of mononuclear Mn(III) cation complexes with hexadentate ligands, the products of the reaction between a N,N′‐bis(3‐aminopropyl)ethylenediamine and salicylaldehydes with the ...different haloid substitutions at the 5 or 3,5 positions, have been synthesized: Mn(5‐F‐sal‐N‐1,5,8,12)BPh4 (1), Mn(3,5‐diCl‐sal‐N‐1,5,8,12)BPh4 (2) and Mn(3,5‐Br,Cl‐sal‐N‐1,5,8,12)BPh4 (3). Their crystal structure, dielectric constant (ϵ) and magnetic properties have been studied. Ligand substituents have a dramatic effect on the structure and magnetic properties of the complexes. With decreasing temperature, the complex (1) shows a gradual spin crossover from the high‐spin state (HS) to the HS:LS intermediate phase, followed by an abrupt transition to the low‐spin state (LS) without changing the crystal symmetry. The complexes 2 and 3 are isostructural, but have fundamentally different properties. Complex 2 demonstrates two structural phase transitions related to sharp spin crossovers from the HS to the HS:LS intermediate phase at 137 K and from the intermediate phase to the LS at 87 K, while complex 3 exhibits only one spin transition from the HS to the HS:LS intermediate phase at 83 K.
Effect of halide substituents on spin and phase transitions in Mn(III) complexes
Abstract Transport of macromolecules through the nuclear envelope (NE) is mediated by nuclear pore complexes (NPCs) consisting of nucleoporins (Nups). Elys/Mel-28 is the Nup that binds and connects ...the decondensing chromatin with the reassembled NPCs at the end of mitosis. Whether Elys links chromatin with the NE during interphase is unknown. Here, using DamID-seq, we identified Elys binding sites in Drosophila late embryos and divided them into those associated with nucleoplasmic or with NPC-linked Elys. These Elys binding sites are located within active or inactive chromatin, respectively. Strikingly, Elys knockdown in S2 cells results in peripheral chromatin displacement from the NE, in decondensation of NE-attached chromatin, and in derepression of genes within. It also leads to slightly more compact active chromatin regions. Our findings indicate that NPC-linked Elys, together with the nuclear lamina, anchors peripheral chromatin to the NE, whereas nucleoplasmic Elys decompacts active chromatin.
As a result of the electrochemical oxidation process, the FeIII(5Cl‐thsa)2− spin‐crossover (SCO) anion with N2S2O2 coordination sphere transforms into N4O2‐coordinated FeIII SCO neutral binuclear ...complex 2 with twist of two disulfide bridges. Each dimeric complex is a binuclear double‐stranded helicate with similar chirality of both Fe centers. The crystal structure of the complex 2 ⋅ 3H2O at 100 K has a monoclinic C2/c space group and contains large cavities (about 21.5 % of the unit cell volume) half‐filled by 3 water molecules per one dimer. The N4O2 coordination of iron(III) with two oxygen atoms (−O−) of phenoxy groups, two imine‐type (−Nim=) nitrogen atoms of azomethine groups, one amidrazone‐type (=NamidH) nitrogen atom and one ionized terminal group (−NionizH) of nitrogen has not been observed in CCDC so far. The oxidation state of the iron atoms in the dimeric complex was confirmed by 57Fe Mössbauer spectroscopy on 90 % enriched 57Fe sample. Mössbauer spectra and dc magnetic measurements demonstrated the partial HS‐HS→LS‐LS SCO in the 185–225 K temperature range. The details of the structure of complex 2 and the features of its magnetic properties were refined by theoretical analysis based on DFT calculations. The B3LYP* functional correctly predicting the energy of the spin‐crossover process was revealed.
In the result of electrochemical oxidation, the SCO FeIII(5Cl‐thsa)2− anion with N2S2O2 coordination sphere transforms into a neutral binuclear N4O2‐coordinated FeIII SCO complex with twisted disulfide bridges and C2 point group.
In this study, crystals of the hybrid layered structure, combined with Fe(III) Spin-Crossover (SCO) complexes with metal-dithiolate anionic radicals, and the precursors with nitrate and iodine ...counterions, are obtained and characterized. Fe(III)(3-OMe-Sal
trien)Ni(dmit)
(
), Fe(III)(3-OMe-Sal
trien)NO
·H
O (
), Fe(III)(3-OMe-Sal
trien)I (
) (3-OMe-Sal
trien = hexadentate N
O
Schiff base is the product of the condensation of triethylenetetramine with 3-methoxysalicylaldehyde; H
dmit = 2-thioxo-1,3-dithiole-4,5-dithiol). Bulk SCO transition was not achieved in the range 2.0-350 K for all three compounds. Alternatively, the hybrid system (
) exhibited irreversible segregation into the spatial fractions of Low-Spin (LS) and High-Spin (HS) phases of the ferric moiety, induced by thermal cycling. Fractioning was studied using both SQUID and EPR methods. Magnetic properties of the LS and HS phases were analyzed in the framework of cooperative interactions with anionic sublattice: Anion radical layers Ni(dmit)
(
), and H-bonded chains with NO
and I (
,
). LS phase of (
) exhibited unusual quasi-two-dimensional conductivity related to the Arrhenius mechanism in the anion radical layers,
= 2 × 10
Ohm·cm and
= 7 × 10
Ohm·cm at 293 K. Ground spin state of the insulating HS phase was distinctive by ferromagnetically coupled spin pairs of HS Fe
,
= 5/2, and metal-dithiolate radicals,
= 1/2.
A series of six seven-coordinate pentagonal-bipyramidal (PBP) erbium complexes, with acyclic pentadentate N3O2 Schiff-base ligands, 2,6-diacetylpyridine bis-(4-methoxybenzoylhydrazone) H2DAPMBH, or ...2,6-diacethylpyridine bis(salicylhydrazone) H4DAPS, and various apical ligands in different charge states were synthesized: Er(DAPMBH)(C2H5OH)Cl (1); Er(DAPMBH)(H2O)Cl·2C2H5OH (2); Er(DAPMBH)(CH3OH)Cl (3); Er(DAPMBH)(CH3OH)(N3) (4); (Et3H)N+Er(H2DAPS)Cl2− (5); and (Et3H)N+Y0.95Er0.05(H2DAPS)Cl2− (6). The physicochemical properties, crystal structures, and the DC and AC magnetic properties of 1–6 were studied. The AC magnetic measurements revealed that most of Compounds 1–6 are field-induced single-molecule magnets, with estimated magnetization energy barriers, Ueff ≈ 16–28 K. The experimental study of the magnetic properties was complemented by theoretical analysis based on ab initio and crystal field calculations. An experimental and theoretical study of the magnetism of 1–6 shows the subtle impact of the type and charge state of the axial ligands on the SMM properties of these complexes.
Two one-dimensional cyano-bridged coordination polymers, namely, {MnII(dapsc)MnIII(CN)6K(H2O)2.75(MeOH)0.5} n ·0.5n(H2O) (I) and {MnII(dapsc)MnIII(CN)6K(H2O)2(MeOH)2} n (II), based on ...alternating high-spin MnII(dapsc) (dapsc = 2,6-diacetylpyridine bis(semicarbazone)) complexes and low-spin orbitally degenerate hexacyanomanganate(III) complexes were synthesized and characterized structurally and magnetically. Static and dynamic magnetic measurements reveal a single-chain magnet (SCM) behavior of I with an energy barrier of U eff ≈ 40 K. Magnetic properties of I are analyzed in detail in terms of a microscopic theory. It is shown that compound I refers to a peculiar case of SCM that does not fall into the usual Ising and Heisenberg limits due to unconventional character of the MnIII–CN–MnII spin coupling resulting from a nonmagnetic singlet ground state of orbitally degenerate complexes MnIII(CN)63–. The prospects of MnIII(CN)63– complex as magnetically anisotropic molecular building block for engineering molecular magnets are critically analyzed.
The utility of DNA Barcoding for species identification and discovery has catalyzed a concerted effort to build the global reference library; however, many animal groups of economical or ...conservational importance remain poorly represented. This study aims to contribute DNA barcode records for all ground squirrel species (Xerinae, Sciuridae, Rodentia) inhabiting Eurasia and to test efficiency of this approach for species discrimination. Cytochrome c oxidase subunit 1 (COI) gene sequences were obtained for 97 individuals representing 16 ground squirrel species of which 12 were correctly identified. Taxonomic allocation of some specimens within four species was complicated by geographically restricted mtDNA introgression. Exclusion of individuals with introgressed mtDNA allowed reaching a 91.6% identification success rate. Significant COI divergence (3.5-4.4%) was observed within the most widespread ground squirrel species (Spermophilus erythrogenys, S. pygmaeus, S. suslicus, Urocitellus undulatus), suggesting the presence of cryptic species. A single putative NUMT (nuclear mitochondrial pseudogene) sequence was recovered during molecular analysis; mitochondrial COI from this sample was amplified following re-extraction of DNA. Our data show high discrimination ability of 100 bp COI fragments for Eurasian ground squirrels (84.3%) with no incorrect assessments, underscoring the potential utility of the existing reference librariy for the development of diagnostic 'mini-barcodes'.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
![[M II (H 2 dapsc)]-[Cr(CN) ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1420-3049_1433-1373/small "[M II (H 2 dapsc)]-[Cr(CN) 6 ] (M = Mn, Co) Chain and Trimer Complexes: Synthesis, Crystal Structure, Non-Covalent Interactions and Magnetic Properties")
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