Single crystalline bulk assemblies of metal halide clusters
show
great potential as highly efficient light emitters with tunable photophysical
properties. However, synthetic control of the geometry of the clusters
in a rational manner has not been well established, and the relationships
between the photophysical properties and structures of this emerging
class of zero-dimensional materials are still not well understood.
Here, we report the synthesis and characterization of two bulk assemblies
of lead bromide clusters, (bmpy)6[Pb3Br12] (T1) and (bmpy)9[ZnBr4]2[Pb3Br11] (T2) (bmpy:
1-butyl-1-methylpyrrolidinium), which contain metal halide trimer
clusters with different geometries. T1 with chain-shaped
[Pb3Br12]6– clusters is not
emissive at room temperature, whereas T2 with triangle-shaped
[Pb3Br11]5– clusters exhibits
yellowish-green emission peaked at 564 nm with a photoluminescence
quantum efficiency of 7% at room temperature. Detailed analysis of
the structural and photophysical properties show that the photophysical
properties and excited-state dynamics of these materials are highly
dependent on the geometry of the metal halide clusters.
An approach to obtaining substantial
amounts of data from a hazardous starting material that can only be
obtained and handled in small quantities is demonstrated by the investigation
of a single small-scale reaction of cyclooctatetraene, C8H8, with a solution obtained from the reduction of Cp′3Pu (Cp′ = C5H4SiMe3) with potassium graphite. This one reaction coupled with oxidation
of a product has provided single-crystal X-ray structural data on
three organoplutonium compounds as well as information on redox chemistry
thereby demonstrating an efficient route to new reactivity and structural
information on this highly radioactive element. The crystal structures
were obtained from the reduction of C8H8 by
a putative Pu(II) complex, (Cp′3PuII)1−, generated in situ, to form the Pu(III) cyclooctatetraenide
complex, [K(crypt)][(C8H8)2PuIII], 1-Pu, and the tetra(cyclopentadienyl) Pu(III)
complex, [K(crypt)][Cp′4PuIII], 2-Pu. Oxidation of the sample of 1-Pu with Ag(I)
afforded a third organoplutonium complex that has been structurally
characterized for the first time, (C8H8)2PuIV, 3-Pu. Complexes 1-Pu and 3-Pu contain Pu sandwiched between parallel (C8H8)2– rings. The (Cp′4PuIII)− anion in 2-Pu features three η5-Cp′ rings and one η1-Cp′ ring, which is a rare example of a formal Pu–C
η1-bond. In addition, this study addresses the challenge
of small-scale synthesis imparted by radiological and material availability
of transuranium isotopes, in particular that of pure metal samples.
A route to an anhydrous Pu(III) starting material from the more readily
available PuIVO2 was developed to facilitate
reproducible syntheses and allow complete spectroscopic analysis of 1-Pu and 2-Pu. PuIVO2 was
converted to PuIIIBr3(DME)2 (DME
= CH3OCH2CH2OCH3) and
subsequently PuIIIBr3(THF)
x
, which was used to independently synthesize 1-Pu, 2-Pu, and 3-Pu.
In
this study, the synthesis, characterization, and pressure response
of a 1D californium mellitate (mellitate = 1,2,3,4,5,6-benzenehexacarboxylate)
coordination polymer, Cf2(mell)(H2O)10·4H2O (Cf-1), are reported. The Cf–O
lengths within the crystal structure are compared to its gadolinium
(Gd-1) and holmium (Ho-1) analogs as well.
These data show that the average Cf–O bond distance is slightly
longer than the average Gd–O bond, consistent with trends in
effective ionic radii. UV–vis-NIR absorption spectra as a function
of pressure were collected using diamond-anvil techniques for both Cf-1 and Ho-1. These experiments show that the
Cf(III) f → f transitions have a stronger dependence on pressure
than that of the holmium analog. In the former case, the shift is
nearly linear with applied pressure and averages 6.6 cm–1/GPa, whereas in the latter, it is <3 cm–1/GPa.
The mellitate ion is relevant in
spent nuclear fuel processing
and is utilized as a surrogate for studying the interactions of f
elements with humic acids. A wealth of different coordination modes
gives the potential for diverse structural chemistry across the actinide
series. In this study, an americium mellitate, 243Am2[(C6(COO–)6](H2O)8·2H2O (1-Am), has
been synthesized and characterized using structural analysis and spectroscopy
at ambient and elevated pressures. 1-Am was then compared
to isomorphous neodymium (1-Nd) and samarium (1-Sm) mellitates via bond-length analysis and pressure dependence of
their Laporte-forbidden f → f transitions. Results show that
the pressure dependence of the f → f transitions of 1-Am is significantly greater than that observed in 1-Nd and 1-Sm, with average shifts of 21.4, 4.7, and 3.6
cm–1/GPa, respectively. This greater shift found
in 1-Am shows further evidence that the 5f orbitals are
more affected than the 4f orbitals when pressure is applied to isostructural
compounds.
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