153 research outputs found
Inclusion Chemistry of Thiazyl and Selenazyl Radicals in MIL-53(Al)
Host-guest interactions have recently become a growing area of study within the scientific community, where the intrinsic chemistry affiliated with the binding and activity of these interactions can be directly correlated to the applications these complexes possess, such as gas storage materials, sensors, activators, and in heterogeneous catalysis. In particular, inclusion complexes possessing radical guests offer the potential for strong communication between both the host and guest and/or the guest molecules themselves, where the nature of the host-guest interactions lead to the effects in which the host can modify the guest properties, or conversely, the guest affects the host structure. This presentation will describe the inclusion chemistry of 4-phenyl-1,2,3,5-dithiadiazolyl (PhDTDA) radical, and its selenium analogue (PhDSDA), into the porous metal-organic framework host MIL-53(Al). The inclusion of the PhDTDA and PhDSDA radicals into MIL-53(Al) was achieved through gas phase diffusion, and led to a colour change in the host from white to red and purple, respectively. The characterization of these inclusion complexes was confirmed through powder X-Ray diffraction and EPR spectroscopy. Reactivity studies of these radicals within the host framework will be discussed
Structural studies of Perfluoroaryldiselenadiazolyl Radicals: Insights into Dithiadiazolyl Chemistry
Synopsis
Diselenadiazolyls exhibit a stronger tendency to dimerize in the solid state than their corresponding dithiadiazolyl (DTDA) radicals, reflected in a range of dimerization modes for (p-XC6F4CNSeSeN)2, which contrast with those of the monomeric DTDA radicals, p-XC6F4CNSSN. The structure of (p-NCC6F4CNSeSeN)2 reflects a buildup of molecular strain in order to accommodate both dimerization and structure-directing CN···Se contacts, whereas the suppression of dimerization releases molecular strain yet retains structure-directing CN···S contacts for the corresponding DTDA radical
Synthesis of bis(trithio)phosphines by oxidative transfer of phosphorus(I)
The synthesis of novel trithiobisphosphines is achieved by oxidative addition of tetrathiocins to the phosphorus(I) reagent [PIdppe][Br] in good yields under ambient conditions. These trithiobisphosphines and the related intermediate diphosphine species are characterized by X-ray diffraction and multinuclear NMR and a mechanism is proposed for the formation of these molecules
Neural Networks and the Classification of Active Galactic Nucleus Spectra
The use of Artificial Neural Networks (ANNs) as a classifier of digital
spectra is investigated. Using both simulated and real data, it is shown that
neural networks can be trained to discriminate between the spectra of different
classes of active galactic nucleus (AGN) with realistic sample sizes and
signal-to-noise ratios. By working in the Fourier domain, neural nets can
classify objects without knowledge of their redshifts.Comment: 11 pages, LaTeX, including two postscript figures, 41 kb. Accepted
for publication in Publ. AS
Synthesis, Structural, Magnetic and Computational Studies of a One-Dimensional Ferromagnetic Cu(II) Chain Assembled from a New Schiff Base Ligand
A new asymmetrically substituted ONOO Schiff base ligand N-(2′-hydroxy-1′-naphthylidene)-3-amino-2-naphthoic acid (nancH2) was prepared from the condensation of 2–hydroxy–1–naphthaldehyde and 3–amino–2–naphthoic acid. nancH2 reacts with Cu2(O2CMe)4·2H2O in the presence of Gd(O2CMe)3·6H2O to afford a uniform one-dimensional homometallic chain, [CuII(nanc)]n (1). The structure of 1 was elucidated via single crystal X-ray diffraction studies, which revealed that the Cu(II) ions adopt distorted square planar geometries and are coordinated in a tridentate manner by an [ONO] donor set from one nanc2− ligand and an O− of a bridging carboxylate group from a second ligand. The bridging carboxylato group of the nanc2− ligand adopts a syn, anti-η1:η1:μ conformation linking neighboring Cu(II) ions, forming a 1D chain. The magnetic susceptibility of 1 follows Curie–Weiss law in the range 45–300 K (C = 0.474(1) emu K mol-1, θ = +7.9(3) K), consistent with ferromagnetic interactions between S = ½ Cu(II) ions with g = 2.248. Subsequently, the data fit well to the 1D quantum Heisenberg ferromagnetic (QHFM) chain model with g = 2.271, and J = +12.3 K. DFT calculations, implementing the broken symmetry approach, were also carried out on a model dimeric unit extracted from the polymeric chain structure. The calculated exchange coupling via the carboxylate bridge (J = +13.8 K) is consistent with the observed ferromagnetic exchange between neighbouring Cu(II) centres. © 2023 by the authors.
This article belongs to the Special Issue Coordination Chemistry: Current Developments and Future Perspectives — a Themed Issue in Honor of Professor Spyros P. Perlepes on the Occasion of His 70th Birthday)
This article contains supplementary material. It is available for download as a supplementary file
Inclusion of a dithiadiazolyl radical in a seemingly non-porous solid
Inclusion of the dithiadiazolyl radical PhCNSSN• into the dynamically porous metallocycle [Cu2(L1)2Cl4], where L1 is the bidentate ligand 1,3-bis(imidazol-1-ylmethyl)-2,4,6- trimethylbenzene, has been achieved by gas phase diffusion. Single crystal X-ray diffraction, powder X-ray diffraction, UV-visible spectroscopy, EPR and SQUID magnetometry studies confirm inclusion of the radical into this seemingly non-porous material, and illustrate the presence of antiferromagnetic coupling between the paramagnetic host and guest species. The radical guest is readily released by heating or by the addition of solvent (CH2Cl2)
Supramolecular aggregation in dithia-arsoles: chlorides, cations and N-centred paddlewheels
The benzo-fused dithia-chloro-arsole derivative C6H4S2AsCl (1) is found to crystallise in the triclinic space group P[1 with combining macron] with 17 molecules in the asymmetric unit whereas the tolyl derivative, MeC6H3S2AsCl (2) is polymorphic with the α-phase crystallising in the monoclinic space group P21/c with a single molecule in the asymmetric unit and the β-phase adopting a triclinic structure with two molecules in the asymmetric unit. Reaction of these dithia-chloro-arsole derivatives with LiN(SiMe3)2 in a 3 : 1 mole ratio afforded the unique paddlewheel structure (MeC6H4S2As)3N (4)
Magnetic interactions in thiazyl-based magnets: The role of the charge and spin densities
The crystal structure of the organic radical p-O2NC6F4CNSSN was
determined at 20 K through a single-crystal neutron-diffraction
experiment. It crystallises in the tetragonal space group P41212,
unchanged from a previous single-crystal X-ray diffraction
experiment at 220 K although there are some changes in molecular
geometry and intermolecular contacts arising from the contraction
of the unit cell. Polarized neutron diffraction at 1.5 K revealed that
the spin distribution is predominantly localised on the N and S
atoms of the heterocyclic ring with a small negative spin density
on the heterocyclic C atom. Spin populations determined using a
multipolar analysis were -0.06, +0.25 and +0.28 on the C, N and S
sites, respectively. These spin populations are in excellent agreement
with both ab-initio DFT calculations (spin populations on the C, N
and S sites of -0.07, 0.22 and 0.31, respectively) and cw-EPR studies
which estimated the spin population on the N site as 0.24. The DFT
calculated spin density revealed less than 1% spin delocalisation
onto the perfluoroaryl ring, several orders of magnitude lower than
the density on the heterocyclic ring. cw-ENDOR studies at both
X-band (9 GHz) and Q-band (34 GHz) frequencies probed the spin
populations at the two chemically distinct F atoms. These spin
populations on the F atoms ortho and meta to the dithiadiazolyl
ring are of magnitude 10-3 and 10-4 respectively. Additional high-resolution single-crystal X-ray diffraction studies at 100 K analysed
within the atoms-in-molecules (AIM) framework gave detailed
information on the charge density distributio
Structure-property-reactivity studies on dithiaphospholes
The reaction of either toluene-3,4-dithiol or benzene dithiol with phosphorus(III) trihalides generates the
corresponding benzo-fused 1,3,2-dithiaphospholes, RC6H3S2PX (R = Me (1), R = H (2); X = Cl, Br, I).
The P-chloro-dithiaphospholes undergo: (a) halogen abstraction reactions with Lewis acids forming
phosphenium cations; (b) substitution with LiHMDS base and; (c) reduction chemistry with sodium metal
to generate the P–P σ-bonded dimer, (RC6H3S2P)2. Reduction catalysis of aldehydes with pinacolborane
using dithiaphospholes is compared with their dioxaphosphole and diazaphosphole counterparts as precatalysts,
revealing interesting differences in the reactivity of this series of compounds
Effects of Halo-substitution on 2'-Chloro-5'-halo-phenyl-1,2,3,5-dithiadiazolyl Radicals: A Crystallographic, Magnetic and EPR Case Study
The syntheses and characterization of the aryl-substituted dithiadiazolyls, 2ʹ-Cl-5ʹ-
X-C6H3CNSSN• [1 (X = F), 2 (X = Cl), 3 (X = Br), 4 (X = I)] are described. In all four cases the
radicals adopt distorted stacks of π*-π* dimers with inter-stack S···X contacts. In 1 (monoclinic
P2/c) S···Cl contacts are manifested through a non-crystallographic 3-fold axis forming
supramolecular trimers whereas the inter-stack S…X contacts in 2 (triclinic P-1), 3 and 4 (which
form an isostructural pair, orthorhombic Pna21) form supramolecular chains. While all the
structures adopt π*-π* cis-oid dimer motifs, tuning the halogen modifies the intra-dimer S···S
distance. Variable temperature SQUID magnetometry and X-band CW-EPR studies revealed the
presence of a thermally accessible triplet state in all cases, with the singlet-triplet separation
appearing in the order 1 > 2 > 3 > 4, consistent with a reduction in the overlap integral with
increasing intra-dimer S···S separation. Variable temperature structural studies on both 2 and 4
reveal a structural evolution from a distorted π-stack motif towards a regular π-stacked array on
warming. This is particularly pronounced in 2 where the intermolecular S…S separations along
the stacking direction converge on a regular 3.6 Å spacing at ambient temperature
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