213 research outputs found
Slow Relaxation of Magnetization in an Isostructural Series of Zinc–Lanthanide Complexes: An Integrated EPR and AC Susceptibility Study
We report the synthesis, structure, and spectroscopic and dynamic magnetic properties of a series of heterodinuclear complexes, [ZnLn(LH4 )2 ](NO3 )3 â
6âH2 O (Ln=Nd, Tb, Dy, Ho, Er, and Yb), with the singly deprotonated form of a new compartmentalized Schiff-base ligand, LH5 . The Ln(III) ions in these systems show a distorted square-antiprism geometry with an LnO8 coordination sphere. EPR spectroscopy and DC magnetic studies have shown that the anisotropic nature of the complexes is far more complicated than predicted on the basis of a simple electrostatic model. Among the investigated systems, only the Dy(III) derivative showed single-ion magnet behavior, in zero and an applied magnetic field, both in pure polycrystalline samples and in a series of polycrystalline samples with different degrees of dilution at the single-crystal level in the isostructural Y(III) derivative. The rich dynamics observed as functions of frequency, field, and temperature reveals that multiple relaxation mechanisms are at play, resulting in a barrier of 189â
cm(-1) , which is among the highest reported for a dinuclear Zn-Dy system. Analysis of the dynamic behavior as a function of dilution degree further evidenced the persistence of non-negligible intermolecular interactions, even at the lowest concentration of 1â%
Constructing Robust Channel Structures by Packing Metallacalixarenes: Reversible Single-Crystal-to-Single-Crystal Dehydration
The self-assembly process involving the dianion of trimesic acid (Htrim2â) and {Cu(tmen)}2+ templating cations (tmen = N,N,NâČ,NâČ-tetramethylethylenediamine) affords a new metallacalixarene, [Cu4(tmen)4(Htrim)4]·nH2O. The packing of the cyclic molecules in the crystal generates channels that are filled by water molecules. The dehydrationârehydration process of the crystals was found to be reversible
Conducting mixed-valence salt of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with the paramagnetic heteroleptic anion [CrIII(oxalate)2(2,2âČ-bipyridine)](-)
The synthesis and crystal structure of the first tetrathiafulvalene (TTF) based radical cation salt containing the heteroleptic paramagnetic anion [CrIII(2,2âČ-bipy)(C2O4)2]â are reported. In the salt formulated as αâČ-(BEDT-TTF)2[Cr(C2O4)2(2,2âČ-bipy)]·CHCl2CH2Cl according to the single-crystal X-ray structure, the BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) donors are in a mixed valence state and form two types of uniform chains within organic layers. Two overlap modes are observed in these chains, which are canted with respect to the stacking direction, leading to a peculiar αâČ packing mode. The anions organize in supramolecular chains sustained by ÏâÏ interactions between the bipyridine units. The magnetic behavior of the compound follows a CurieâWeiss law, with a magnetic contribution arising from both cationic and anionic counterparts. Single-crystal electrical transport measurements are in agreement with a semiconductor behavior and have been correlated with extended HĂŒckel tight-binding calculations
Stereoisomeric semiconducting radical cation salts of chiral bis(2-hydroxypropylthio)ethylenedithioTTF with tetrafluoroborate anions
The new chiral TTF-based donor molecule bis(2-hydroxypropylthio)ethylenedithiotetrathiafulvalene has produced enantiopure R,R and S,S radical cation salts with the tetrafluoroborate anion as well as the nearly isostructural meso/racemate mixture. The enantiopure R,R or S,S salts are both 1:1 semiconducting salts with activation energies of 0.19â0.24 eV, both crystallising in the orthorhombic space group C2221. The semiconducting salt containing both meso and racemic donor cations has a very similar crystal structure but crystallising in the monoclinic space group C2/c (ÎČ = 91.39°) with similar SâŻS interactions but a smaller activation energy of 0.15â0.17 eV. This is in contrast to previous families of this type where the disordered racemate has a larger activation energy than its enantiopure salts
New heterometallic coordination polymers constructed from 3dâ3dâČ binuclear nodes
Heterobinuclear [CuIIMnII] and [CuIICoII] cationic complexes can efficiently act as nodes for designing coordination polymers. The crystal structures of two binuclear precursors, [LCuCo(NO3)2] (1) and [LCuMn(NO3)2] (2), have been solved (L2â is the dianion of the Schiff base resulting from the 2 : 1 condensation of 3-methoxysalicyladehyde with 1,3-propanediamine). The nitrato ligands, coordinated to CoII and, respectively, the MnII ions from the precursors, are easily replaced by exo-dentate ligands, resulting in 1-D coordination polymers: 1â[L(H2O)CuCo(oxy-bbz)]·CH3CN·C2H5OH (3), 1â[L(H2O)CuCo(2,5-dhtp)]·CH3CN (5) and â[L(H2O)CuMn(ox)]·3H2O (6) (oxy-bbz2â = the dianion of 4,4âČ-oxy-bis(benzoic) acid; 2,5-dhtp2â = the dianion of 2,5-dihydroxy-terephthalic acid; ox2â = the dianion of the oxalic acid). In the case of the [CuMn] node, the interaction with oxy-bbz2â affords a binuclear complex, [LCuMn(oxy-bbz)(H2O)2] (4)
Quantum Origins of Molecular Recognition and Olfaction in Drosophila
The standard model for molecular recognition of an odorant is that receptor
sites discriminate by molecular geometry as evidenced that two chiral molecules
may smell very differently. However, recent studies of isotopically labeled
olfactants indicate that there may be a molecular vibration-sensing component
to olfactory reception, specifically in the spectral region around 2300
cm. Here we present a donor-bridge-acceptor model for olfaction which
attempts to explain this effect. Our model, based upon accurate quantum
chemical calculations of the olfactant (bridge) in its neutral and ionized
states, posits that internal modes of the olfactant are excited impulsively
during hole transfer from a donor to acceptor site on the receptor,
specifically those modes that are resonant with the tunneling gap. By
projecting the impulsive force onto the internal modes, we can determine which
modes are excited at a given value of the donor-acceptor tunneling gap. Only
those modes resonant with the tunneling gap and are impulsively excited will
give a significant contribution to the inelastic transfer rate. Using
acetophenone as a test case, our model and experiments on D. melanogaster
suggest that isotopomers of a given olfactant give rise to different odorant
qualities. These results support the notion that inelastic scattering effects
play a role in discriminating between isotopomers, but that this is not a
general spectroscopic effectComment: 7 pages, 3 figure
Charge-sensitive vibrational modes in the (EDT-TTF-OX)2AsF6 chiral molecular conductors
Infrared and Raman spectra of three chiral molecular conductors (EDT-TTF-OX)2AsF6, comprising of two salts based on enantiopure EDT-TTF-OX donor molecules and one based on their racemic mixture, have been measured as a function of temperature. In the frequency range of the C=C stretching vibrations of EDT-TTF-OX, charge-sensitive modes are identified based on theoretical calculations for neutral and oxidized EDT-TTF-OX using density functional theory (DFT) methods. The positions of C=C stretching modes in both Raman and infrared spectra of the (EDT-TTF-OX)2AsF6Â materials are analyzed assuming a linear relationship between the frequency and charge of the molecule. The charge density on the EDTTTF-OX donor molecule is estimated to be +0.5 in all investigated materials and does not change with temperature. Therefore we suggest, that M-I transition observed in (EDT-TTF-OX)2AsF6Â chiral molecular conductors at low temperature is not related to the charge ordering mechanism
Chirality in charge-transfer salts of BEDT-TTF of tris(oxalato)chromate(III)
Crystallisation from chiral electrolyte (R)-(â)-carvone has produced three new chiral semiconducting salts of BEDT-TTF from racemic anion tri(oxalato)chromate(III)
Dimers and chains of {3d-4f} single molecule magnets constructed from heterobimetallic tectons.
International audienceA tetranuclear complex and a 1-D coordination polymer with a ladder-like topology have been obtained by connecting [Ni(II)Dy(III)] nodes with dicarboxylato ligands: [Niâ(valpn)âDyâ(III)(pdca)â(NOâ)(HâO)â](NOâ)*4HâO 1, and (â)Âč[Niâ(HâO)â(valpn)âDyâ(tfa)â]*4CHâCN 2 (valpnÂČâ» = the dianion of the Schiff base resulting from reacting o-vanillin with 1,3-propanediamine; pdcaÂČâ» = the dianion of 2,6-pyridinedicarboxylic acid; tfaÂČâ» = the dianion of the terephthalic acid). The magnetic measurements show a ferromagnetic interaction between Ni(II) and Dy(III), and that both compounds behave like SMM with strong tunnelling. The barrier of 2 (17.4 K) is higher than that of 1 (13.6 K)
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