12 research outputs found
Drug prevention and schools: a comparison of current drug education in Luton high schools with the advice given in the DFE Circular 4/95
Drug prevention and schools: a comparison of current drug education in Luton high schools with the advice given in the DFE Circular 4/9
Synthesis of the I–K Fused Polyether Array of CTX3C and Related Ciguatoxins by Use of a Gold-Catalyzed Cyclization Reaction
The I–K fragment
(C31–C49) of the ciguatoxin CTX3C
has been synthesized from a simple chiral pool derived tetrahydropyranyl
alcohol. An efficient gold-catalyzed cyclization reaction of a γ′-hydroxy
ynone has been used to accomplish efficient closure of ring K under
mild conditions. The resulting vinylogous ester has been elaborated
to give a complete tricyclic fragment bearing the dimethyl-substituted
side chain required for assembly of the LM spirocyclic acetal portion
of the target
Furosemide Cocrystals: Structures, Hydrogen Bonding, and Implications for Properties
In this paper, we report the crystal
growth of four cocrystals
of furosemide (4-chloro-2-[(2-furanylmethyl)amino]-5-sulfamoylbenzoic
acid), a loop diuretic drug used for the treatment of hypertension
and edemas, prepared with <i>p</i>-aminobenzoic acid, nicotinamide,
and isonicotinamide as coformers. We present four new crystal structures
and elucidate the intermolecular interactions present in the cocrystals.
The structures display interesting supramolecular chemistry: a number
of different synthons, as well as short strong hydrogen bonds with
partial proton transfer and indications of proton disorder. Using
powder X-ray diffraction, solid state NMR, and thermal analysis, we
provide evidence for the preparation of bulk samples of two compositions,
namely, the 1:1 cocrystal of furosemide and <i>p</i>-aminobenzoic
acid and 2:1 cocrystal of furosemide and isonicotinamide, highlighting
the general necessity of such multitechnique approaches to characterize
organic solids (including cocrystals and solvates) prepared by grinding
methods. Finally, we correlate the structural features reported for
the first time in this work with the previously published pharmacologically
relevant properties (solubility and intrinsic dissolution rate) of
the furosemide cocrystals
Synthetic Considerations in the Self-Assembly of Coordination Polymers of Pyridine-Functionalized Hybrid Mn-Anderson Polyoxometalates
The
incorporation of polyoxometalates (POMs) as structural units
into ordered porous constructs such as metal–organic frameworks
(MOFs) is desirable for a range of applications where intrinsic properties
inherited from both the MOF and POM are utilized, including catalysis
and magnetic data storage. The controlled self-assembly of targeted
MOF topologies containing POM units is hampered by the wide range
of oxo and hydroxo units on the peripheries of POMs that can act as
coordinating groups toward linking metal cations leading to a diverse
range of structures, but incorporation of organic donor units into
hybrid POMs offers an alternative methodology to programmably synthesize
POM/MOF conjugates. Herein, we report six coordination polymers obtained
serendipitously wherein Zn<sup>2+</sup> and Cu<sup>2+</sup> link pyridine-appended
Mn-Anderson clusters into two- and three-dimensional network solids
with complex connectivities and topologies. Careful inspection of
their solid-state structures has allowed us to identify common structure-directing
features across these coordination polymers, including a square motif
where two Zn<sup>2+</sup> cations bridge two POMs. By correlating
certain structural motifs with synthetic conditions, we have formulated
a series of design considerations for the self-assembly of coordination
polymers of hybrid POMs, encompassing the selection of reaction conditions,
coligands, and linking metal cations. We anticipate that these synthetic
guidelines will inform the future assembly of hybrid POMs into functional
MOF materials
Symes_Supplementary information_ESM.doc from An investigation into the unusual linkage isomerization and nitrite reduction activity of a novel tris(2-pyridyl) copper complex
1H and 13C NMR spectra of compound 1, deconvoluted calculated IR spectra for [Cu1(NO2)2] and additional crystallographic data for [Cu1(NO2)2]
SO<sub>2</sub> Phototriggered Crystalline Nanomechanical Transduction of Aromatic Rotors in Tosylates: Rationalization via Photocrystallography of [Ru(NH<sub>3</sub>)<sub>4</sub>SO<sub>2</sub>X]tosylate<sub>2</sub> (X = pyridine, 3‑Cl-pyridine, 4‑Cl-pyridine)
Thermally
reversible solid-state linkage SO<sub>2</sub> photoisomers of three
complexes in the [Ru(NH<sub>3</sub>)<sub>4</sub>SO<sub>2</sub><b>X</b>]tosylate<sub>2</sub> family are captured in their metastable
states using photocrystallography, where <b>X</b> = pyridine
(<b>1</b>), 3-Cl-pyridine (<b>2</b>), and 4-Cl-pyridine
(<b>3</b>). This photoisomerism exists only in the single-crystal
form; accordingly, the nature of the crystalline environment surrounding
the photoactive species controls its properties. In particular, the
structural role of the tosylate anion needs to be understood against
possible chemical influences due to varying the <i>trans</i> ligand, <b>X</b>. The photoexcited geometries, photoconversion
levels, and thermal stabilities of the photoisomers that form in <b>1</b>–<b>3</b> are therefore studied. <b>1</b> and <b>2</b> yield two photoisomers at 100 K: the O-bound
end-on η<sup>1</sup>-SO<sub>2</sub> (MS1) configuration and
the side-bound η<sup>2</sup>-SO<sub>2</sub> (MS2); <b>3</b> exhibits only the more thermally stable MS2 geometry. The decay
kinetics of the MS2 geometry for <b>1</b>–<b>3</b> demonstrate that the greater the free volume of the GS SO<sub>2</sub> ligand for a given counterion, the greater the MS2 thermal stability.
Furthermore, a rationalization is sought for the SO<sub>2</sub> phototriggered
molecular rotation of the phenyl ring in the tosylate anion; this
is selectively observed in <b>2</b>, manifesting as nanomechanical
molecular transduction. This molecular transduction was not observed
in <b>1</b>, despite the presence of the MS1 geometry due to
the close intermolecular interactions between the MS1 SO<sub>2</sub> and the neighboring tosylate ion. The decay of this anionic molecular
rotor in <b>2</b>, however, follows a nontraditional decay pathway,
as determined by time-resolved crystallographic analysis; this contrasts
with the well-behaved first-order kinetic decay of its MS1 SO<sub>2</sub> phototrigger
About Living Water
Many
of the desirable properties of metal–organic frameworks
(MOFs) can be tuned by chemical functionalization of the organic ligands
that connect their metal clusters into multidimensional network solids.
When these linker molecules are intrinsically fluorescent, they can
pass on this property to the resultant MOF, potentially generating
solid-state sensors, as analytes can be bound within their porous
interiors. Herein, we report the synthesis of a series of 14 interpenetrated
Zr and Hf MOFs linked by functionalized 4,4′-[1,4-phenylene-bis(ethyne-2,1-diyl)]-dibenzoate
(peb<sup>2–</sup>) ligands, and we analyze the effect of functional
group incorporation on their structures and properties. Addition of
methyl, fluoro, naphthyl, and benzothiadiazolyl units
does not affect the underlying topology, but induces subtle structural
changes, such as ligand rotation, and mediates host–guest interactions.
Further, we demonstrate that solid-state photoluminescence spectroscopy
can be used to probe these effects. For instance, introduction of
naphthyl and benzothiadiazolyl units yields MOFs that
can act as stable fluorescent water sensors, a dimethyl modified MOF
exhibits a temperature dependent phase change controlled by steric
clashes between interpenetrated nets, and a tetrafluorinated analogue
is found to be superhydrophobic despite only partial fluorination
of its organic backbone. These subtle changes in ligand structure
coupled with the consistent framework topology give rise to a series
of MOFs with a remarkable range of physical properties that are not
observed with the ligands alone
Dynamics of Ground and Excited State Vibrational Relaxation and Energy Transfer in Transition Metal Carbonyls
Nonlinear vibrational spectroscopy
provides insights into the dynamics
of vibrational energy transfer in and between molecules, a crucial
phenomenon in condensed phase physics, chemistry, and biology. Here
we use frequency-domain 2-dimensional infrared (2DIR) spectroscopy
to investigate the vibrational relaxation (VR) and vibrational energy
transfer (VET) rates in different solvents in both the electronic
ground and excited states of Re(Cl)(CO)<sub>3</sub>(4,4′-diethylester-2,2′-bipyridine),
a prototypical transition metal carbonyl complex. The strong CO
and ester CO stretch infrared reporters, located on opposite
sides of the molecule, were monitored in the 1600–2100 cm<sup>–1</sup> spectral region. VR in the lowest charge transfer
triplet excited state (<sup>3</sup>CT) is found to be up to eight
times faster than in the ground state. In the ground state, intramolecular
anharmonic coupling may be solvent-assisted through solvent-induced
frequency and charge fluctuations, and as such VR rates are solvent-dependent.
In contrast, VR rates in the solvated <sup>3</sup>CT state are surprisingly
solvent-insensitive, which suggests that predominantly intramolecular
effects are responsible for the rapid vibrational deactivation. The
increased VR rates in the excited state are discussed in terms of
intramolecular electrostatic interactions helping overcome structural
and thermodynamic barriers for this process in the vicinity of the
central heavy atom, a feature which may be of significance to nonequilibrium
photoinduced processes observed in transition metal complexes in general
Systematic and Controllable Negative, Zero, and Positive Thermal Expansion in Cubic Zr<sub>1–<i>x</i></sub>Sn<sub><i>x</i></sub>Mo<sub>2</sub>O<sub>8</sub>
We
describe the synthesis and characterization of a family of materials,
Zr<sub>1–<i>x</i></sub>Sn<sub><i>x</i></sub>Mo<sub>2</sub>O<sub>8</sub> (0 < <i>x</i> < 1), whose
isotropic thermal expansion coefficient can be systematically varied
from negative to zero to positive values. These materials allow tunable
expansion in a single phase as opposed to using a composite system.
Linear thermal expansion coefficients, α<sub>l</sub>, ranging
from −7.9(2) × 10<sup>–6</sup> to +5.9(2) ×
10<sup>–6</sup> K<sup>–1</sup> (12–500 K) can
be achieved across the series; contraction and expansion limits are
of the same order of magnitude as the expansion of typical ceramics.
We also report the various structures and thermal expansion of “cubic”
SnMo<sub>2</sub>O<sub>8</sub>, and we use time- and temperature-dependent
diffraction studies to describe a series of phase transitions between
different ordered and disordered states of this material
Redox Non-innocence of Thioether Crowns: Elucidation of the Electronic Structure of the Mononuclear Pd(III) Complexes [Pd([9]aneS<sub>3</sub>)<sub>2</sub>]<sup>3+</sup> and [Pd([18]aneS<sub>6</sub>)]<sup>3+</sup>
The Pd(II) complexes [Pd([9]aneS<sub>3</sub>)<sub>2</sub>](PF<sub>6</sub>)<sub>2</sub>·2MeCN (<b>1</b>) ([9]aneS<sub>3</sub> = 1,4,7-trithiacyclononane) and [Pd([18]aneS<sub>6</sub>)](PF<sub>6</sub>)<sub>2</sub> (<b>2</b>) ([18]aneS<sub>6</sub> = 1,4,7,10,13,16-hexathiacyclooctadecane)
can be oxidized electrochemically or chemically oxidized with 70%
HClO<sub>4</sub> to [Pd([9]aneS<sub>3</sub>)<sub>2</sub>]<sup>3+</sup> and [Pd([18]aneS<sub>6</sub>)]<sup>3+</sup>, respectively. These
centers have been characterized by single crystal X-ray diffraction,
and by UV/vis and multifrequency electron paramagnetic resonance (EPR)
spectroscopies. The single crystal X-ray structures of [Pd<sup>III</sup>([9]aneS<sub>3</sub>)<sub>2</sub>](ClO<sub>4</sub>)<sub>6</sub>·(H<sub>3</sub>O)<sub>3</sub>·(H<sub>2</sub>O)<sub>4</sub> (<b>3</b>) at 150 K and [Pd([18]aneS<sub>6</sub>)](ClO<sub>4</sub>)<sub>6</sub>·(H<sub>5</sub>O<sub>2</sub>)<sub>3</sub> (<b>4</b>) at
90 K reveal distorted octahedral geometries with Pd–S distances
of 2.3695(8), 2.3692(8), 2.5356(9) and 2.3490(6), 2.3454(5), 2.5474(6)
Å, respectively, consistent with Jahn–Teller distortion
at a low-spin d<sup>7</sup> Pd(III) center. The Pd(II) compound [Pd([9]aneS<sub>3</sub>)<sub>2</sub>](PF<sub>6</sub>)<sub>2</sub> shows a one-electron
oxidation process in MeCN (0.2 M NBu<sub>4</sub>PF<sub>6</sub>, 293
K) at <i>E</i><sub>1/2</sub> = +0.57 V vs. Fc<sup>+</sup>/Fc assigned to a formal Pd(III)/Pd(II) couple. Multifrequency (Q-,
X-, S-, and L-band) EPR spectroscopic analysis of [Pd([9]aneS<sub>3</sub>)<sub>2</sub>]<sup>3+</sup> and [Pd([18]aneS<sub>6</sub>)]<sup>3+</sup> gives <i>g</i><sub><i>iso</i></sub> =
2.024, |<i>A</i><sub><i>iso</i>(Pd)</sub>| = 18.9
× 10<sup>–4</sup> cm<sup>–1</sup>; <i>g</i><sub><i>xx</i></sub> = 2.046, <i>g</i><sub><i>yy</i></sub> = 2.041, <i>g</i><sub><i>zz</i></sub> = 2.004; |<i>A</i><sub><i>xx</i>(Pd)</sub>| = 24 × 10<sup>–4</sup> cm<sup>–1</sup>, |<i>A</i><sub><i>yy</i>(Pd)</sub>| = 22 × 10<sup>–4</sup> cm<sup>–1</sup>, |<i>A</i><sub><i>zz</i>(Pd)</sub>| = 14 ×
10<sup>–4</sup> cm<sup>–1</sup>, |<i>a</i><sub><i>xx</i>(H)</sub>| = 4 × 10<sup>–4</sup> cm<sup>–1</sup>, |<i>a</i><sub><i>yy</i>(H)</sub>| = 5 × 10<sup>–4</sup> cm<sup>–1</sup>, |<i>a</i><sub><i>zz</i>(H)</sub>| = 5.5 × 10<sup>–4</sup> cm<sup>–1</sup> for [Pd([9]aneS<sub>3</sub>)<sub>2</sub>]<sup>3+</sup>, and <i>g</i><sub><i>iso</i></sub> = 2.015, |<i>A</i><sub><i>iso</i>(Pd)</sub>| = 18.8× 10<sup>–4</sup> cm<sup>–1</sup>; <i>g</i><sub><i>xx</i></sub> = 2.048 <i>g</i><sub><i>yy</i></sub> =
2.036, <i>g</i><sub><i>zz</i></sub> = 1.998; |<i>a</i><sub><i>xx(</i>H)</sub>| = 5, |<i>a</i><sub><i>yy(</i>H)</sub>| = 5,
|<i>a</i><sub><i>zz(</i>H)</sub>| = 6 × 10<sup>–4</sup> cm<sup>–1</sup>; |<i>A</i><sub><i>xx</i>(Pd)</sub>| = 23× 10<sup>–4</sup> cm<sup>–1</sup>, |<i>A</i><sub><i>yy</i>(Pd)</sub>| = 22 ×
10<sup>–4</sup> cm<sup>–1</sup>, |<i>A</i><sub><i>zz</i>(Pd)</sub>| = 4 × 10<sup>–4</sup> cm<sup>–1</sup> for [Pd([18]aneS<sub>6</sub>)]<sup>3+</sup>. Both [Pd([9]aneS<sub>3</sub>)<sub>2</sub>]<sup>3+</sup> and [Pd([18]aneS<sub>6</sub>)]<sup>3+</sup> exhibit five-line superhyperfine splitting
in the <i>g</i><sub><i>zz</i></sub> region in
their frozen solution EPR spectra. Double resonance spectroscopic
measurements, supported by density functional theory (DFT) calculations,
permit assignment of this superhyperfine to through-bond coupling
involving four <sup>1</sup>H centers of the macrocyclic ring. Analysis
of the spin Hamiltonian parameters for the singly occupied molecular
orbital (SOMO) in these complexes gives about 20.4% and 25% Pd character
in [Pd([9]aneS<sub>3</sub>)<sub>2</sub>]<sup>3+</sup> and [Pd([18]aneS<sub>6</sub>)]<sup>3+</sup>, respectively, consistent with the compositions
calculated from scalar relativistic DFT calculations