7 research outputs found
Support Effects on Hydrogen Desorption, Isotope Exchange, Chemical Reactivity, and Magnetism of Platinum Nanoclusters in KL Zeolite
Platinum
clusters were prepared by ion exchange of a KL zeolite,
followed by oxygen calcination and hydrogen reduction, and characterized
by electron paramagnetic resonance (EPR) and hyperfine sublevel correlation
experiment (HYSCORE) spectroscopy. Simulations indicate that the cluster
contains 12 equivalent platinum atoms. Therefore, the most likely
structure is an icosahedral or cuboctahedral magic number Pt<sub>13</sub> cluster with 12 platinum atoms at the surface. One atom in the center
possesses only a small spin density. H/D desorption and readsorption
experiments monitored via EPR and HYSCORE measurements provide information
about the structure of the clusters and about the reversibility of
the adsorption/desorption and isotope exchange process. Deuterium
desorption experiments result in a value of 2.1 ± 0.2 eV for
the D<sub>2</sub> desorption energy of the Pt<sub>13</sub> clusters
dispersed in KL zeolite. This is more than double of the value for
a (111) Pt single-crystal surface, revealing a finite size and/or
support effect. Oxygen adsorption on deuterium-covered Pt<sub>13</sub> clusters did not show a vigorous oxyhydrogen reaction. It appears
that the reaction is inhibited by the deuterium coverage
New Selective Synthesis of Dithiaboroles as a Viable Pathway to Functionalized Benzenedithiolenes and Their Complexes
A synthetic protocol
to synthesize 2-bromobenzo-1,3,2-dithiaboroles in one step from easily
accessible benzene bis(isopropyl thioether)s has been developed. The
reaction is remarkably specific in converting substrates with two
adjacent <sup><i>i</i></sup>PrS moieties while leaving isolated
thioether functions and other functional groups intact. On the basis
of the spectroscopic detection or isolation of reaction intermediates,
a mechanistic explanation involving a neighbor-group-assisted dealkylation
as a key step is proposed. The resulting products featuring one or
two dithiaborole units were isolated in good yields and fully characterized.
Subsequent methanolysis, which was carried out either as a separate
reaction step or in the manner of a one-pot reaction, gave rise to
functionally substituted benzenedithiols. The feasibility of a methylphosphoryl-substituted
benzenedithiol to act as a dianionic S,S-chelating ligand was demonstrated
with the formation of paramagnetic Ni(III) and Co(III) complexes.
Selective reduction of the phosphoryl group afforded a rare example
of a phosphino dithiol which was shown to act as a monoanionic P,S-bidentate
ligand toward Pd(II). All complexes were characterized by spectral
data and X-ray diffraction studies, and the paramagnetic ones also
by superconducting quantum interference device magnetometry
Multiple Bistability in Quinonoid-Bridged Diiron(II) Complexes: Influence of Bridge Symmetry on Bistable Properties
Quinonoid bridges
are well-suited for generating dinuclear assemblies that might display
various bistable properties. In this contribution we present two diiron(II)
complexes where the iron(II) centers are either bridged by the doubly
deprotonated form of a symmetrically substituted quinonoid bridge,
2,5-bis[4-(isopropyl)anilino]-1,4-benzoquinone (<b>H</b><sub><b>2</b></sub><b>L2′</b>) with a [O,N,O,N] donor
set, or with the doubly deprotonated form of an unsymmetrically substituted
quinonoid bridge, 2-[4-(isopropyl)anilino]-5-hydroxy-1,4-benzoquinone
(<b>H</b><sub><b>2</b></sub><b>L5′</b>) with
a [O,O,O,N] donor set. Both complexes display temperature-induced
spin crossover (SCO). The nature of the SCO is strongly dependent
on the bridging ligand, with only the complex with the [O,O,O,N] donor
set displaying a prominent hysteresis loop of about 55 K. Importantly,
only the latter complex also shows a pronounced light-induced spin
state change. Furthermore, both complexes can be oxidized to the mixed-valent
iron(II)–iron(III) form, and the nature of the bridge determines
the Robin and Day classification of these forms. Both complexes have
been probed by a battery of electrochemical, spectroscopic, and magnetic
methods, and this combined approach is used to shed light on the electronic
structures of the complexes and on bistability. The results presented
here thus show the potential of using the relatively new class of
unsymmetrically substituted bridging quinonoid ligands for generating
intriguing bistable properties and for performing site-specific magnetic
switching
Magnetic and HFEPR Studies of Exchange Coupling in a Series of μ‑Cl Dicobalt Complexes
We report three dinuclear
cobalt(II) complexes, [Co(L)Cl<sub>2</sub>]<sub>2</sub> (L = bpy,
mbpy, and dmpbt), that are bridged solely by chloride ions. High-field
electron paramagnetic resonance and magnetometric measurements were
applied to investigate the magnetic intramolecular Co–Co interactions.
Simulation results based on the multispin model reveal that the complexes
are weakly ferromagnetically coupled and that the isotropic exchange
coupling constants differ slightly for the three complexes. Moreover,
the competing effects of zero-field splitting and magnetic coupling
on the temperature-dependent magnetic susceptibility were analyzed
Magnetic and HFEPR Studies of Exchange Coupling in a Series of μ‑Cl Dicobalt Complexes
We report three dinuclear
cobalt(II) complexes, [Co(L)Cl<sub>2</sub>]<sub>2</sub> (L = bpy,
mbpy, and dmpbt), that are bridged solely by chloride ions. High-field
electron paramagnetic resonance and magnetometric measurements were
applied to investigate the magnetic intramolecular Co–Co interactions.
Simulation results based on the multispin model reveal that the complexes
are weakly ferromagnetically coupled and that the isotropic exchange
coupling constants differ slightly for the three complexes. Moreover,
the competing effects of zero-field splitting and magnetic coupling
on the temperature-dependent magnetic susceptibility were analyzed
Comprehensive Spectroscopic Determination of the Crystal Field Splitting in an Erbium Single-Ion Magnet
The electronic structure of a novel
lanthanide-based single-ion
magnet, {C(NH<sub>2</sub>)<sub>3</sub>}<sub>5</sub>[Er(CO<sub>3</sub>)<sub>4</sub>]·11H<sub>2</sub>O, was comprehensively studied
by means of a large number of different spectroscopic techniques,
including far-infrared, optical, and magnetic resonance spectroscopies.
A thorough analysis, based on crystal field theory, allowed an unambiguous
determination of all relevant free ion and crystal field parameters.
We show that inclusion of methods sensitive to the nature of the lowest-energy
states is essential to arrive at a correct description of the states
that are most relevant for the static and dynamic magnetic properties.
The spectroscopic investigations also allowed for a full understanding
of the magnetic relaxation processes occurring in this system. Thus,
the importance of spectroscopic studies for the improvement of single-molecule
magnets is underlined
Control of Complex Formation through Peripheral Substituents in Click-Tripodal Ligands: Structural Diversity in Homo- and Heterodinuclear Cobalt-Azido Complexes
The azide anion is widely used as
a ligand in coordination chemistry. Despite its ubiquitous presence,
controlled synthesis of azido complexes remains a challenging task.
Making use of click-derived tripodal ligands, we present here various
coordination motifs of the azido ligands, the formation of which appears
to be controlled by the peripheral substituents on the tripodal ligands
with otherwise identical structure of the coordination moieties. Thus,
the flexible benzyl substituents on the tripodal ligand TBTA led to
the formation of the first example of an unsupported and solely μ<sub>1,1</sub>-azido-bridged dicobalt(II) complex. The more rigid
phenyl substituents on the TPTA ligand deliver an unsupported and
solely μ<sub>1,3</sub>-azido-bridged dicobalt(II) complex.
Bulky diisopropylphenyl substituents on the TDTA ligand
deliver a doubly μ<sub>1,1</sub>-azido-bridged dicobalt(II)
complex. Intriguingly, the mononuclear copper(II) complex [Cu(TBTA)N<sub>3</sub>]<sup>+</sup> is an excellent synthon for generating mixed
dinuclear complexes of the form [(TBTA)Co(μ<sub>1,1</sub>-N<sub>3</sub>)Cu(TBTA)]<sup>3+</sup> or [(TBTA)Cu(μ<sub>1,1</sub>-N<sub>3</sub>)Cu(TPTA)]<sup>3+</sup>, both
of which contain a single unsupported μ<sub>1,1</sub>-N<sub>3</sub> as a bridge. To the best of our knowledge, these are also
the first examples of mixed dinuclear complexes with a μ<sub>1,1</sub>-N<sub>3</sub> monoazido bridge. All complexes were crystallographically
characterized, and selected examples were probed via magnetometry
and high-field EPR spectroscopy to elucidate the electronic structures
of these complexes and the nature of magnetic coupling in the various
azido-bridged complexes. These results thus prove the power of click-tripodal
ligands in generating hitherto unknown chemical structures and properties