3 research outputs found
Abnormally Long-Range Diamagnetic Anisotropy Induced by Cyclic d<sub>δ</sub>–p<sub>π</sub> π Conjugation within a Six-Membered Dimolybdenum/Chalcogen Ring
Incorporating two quadruply bonded dimolybdenum units
[Mo<sub>2</sub>(DAniF)<sub><sup>3</sup></sub>]<sup>+</sup> (ancillary
ligand DAniF
= <i>N</i>,<i>N</i>′-di-<i>p</i>-anisylformamidinate) with two hydroselenides (SeH<sup>–</sup>) gave rise to [Mo<sub>2</sub>(DAniF)<sub>3</sub>]<sub>2</sub>(μ-SeH)<sub>2</sub> (<b>1</b>). With the molecular scaffold remaining unchanged,
aerobic oxidation of <b>1</b>, followed by autodeprotonation,
generated [Mo<sub>2</sub>(DAniF)<sub>3</sub>]<sub>2</sub>(μ-Se)<sub>2</sub> (<b>2</b>). The two complexes share a common cyclic
six-membered Mo<sub>2</sub>/Se core, but compound <b>2</b> is
distinct from <b>1</b> by having structural, electronic, and
magnetic properties that correspond with aromaticity. Importantly,
the aromatic behaviors for this non-carbon system are ascribable to
the bonding analogy between the δ component in a Mo–Mo
quadruple bond and the π component in a C–C double bond.
Cyclic π delocalization via d<sub>δ</sub>–p<sub>π</sub> conjugation within the central unit, which involves
six π electrons with one electron from each of the Mo<sub>2</sub> units and two electrons from each of the bridging atoms, has been
confirmed in a previous work on the oxygen- and sulfur-bridged analogues
(Fang, W.; et al. <i>Chem.î—¸Eur. J.</i> <b>2011</b>, <i>17</i>, 10288). Of the three members in this family,
compound <b>2</b> exhibits an enhanced aromaticity because of
the selenium bridges. The remote in-plane and out-of-plane <i>methine</i> (ArNC<i>H</i>NAr) protons resonate at
chemical shifts (δ) 9.42 and 7.84 ppm, respectively. This NMR
displacement, Δδ = 1.58 ppm, is larger than that for the
oxygen-bridged (1.30 ppm) and sulfur-bridged (1.49 ppm) derivatives.
The abnormally long-range shielding effects and the large diamagnetic
anisotropy for this complex system can be rationalized by the induced
ring currents circulating the Mo<sub>2</sub>/chalcogen core. By employment
of the McConnell equation {Δσ = ΔχÂ[(l –
3 cos 2θ)/3<i>R</i><sup>3</sup><i>N</i>]},
the magnetic anisotropy (Δχ = χ<sub>⊥</sub> – χ<sub>||</sub>) is estimated to be −414 ppm
cgs, which is dramatically larger than −62.9 ppm cgs for benzene,
the paradigm of aromaticity. In addition, it is found that the magnitude
of Δχ is linearly related to the radius of the bridging
atoms, with the selenium analogue having the largest value. This aromaticity
sequence is in agreement with that for the chalcogen-containing aromatic
family, e.g., furan < thiophene < selenophene
Perovskite-Structured PbTiO<sub>3</sub> Thin Films Grown from a Single-Source Precursor
Perovskite-structured
lead titanate thin films have been grown on FTO-coated glass substrates
from a single-source heterometallic molecular complex, [PbTiÂ(μ<sub>2</sub>-O<sub>2</sub>CCF<sub>3</sub>)<sub>4</sub>(THF)<sub>3</sub>(μ<sub>3</sub>-O)]<sub>2</sub> (<b>1</b>), which was
isolated in quantitative yield from the reaction of tetraacetatoleadÂ(IV),
tetrabutoxytitaniumÂ(IV), and trifluoroacetic acid from a tetrahydrofuran
solution. Complex <b>1</b> has been characterized by physicochemical
methods such as melting point, microanalysis, FTIR, <sup>1</sup>H
and <sup>19</sup>F NMR, thermal analysis, and single-crystal X-ray
diffraction (XRD) analysis. Thin films of lead titanate having spherical
particles of various sizes have been grown from <b>1</b> by
aerosol-assisted chemical vapor deposition at 550 °C. The thin
films have been characterized by powder XRD, scanning electron microscopy,
and energy-dispersive X-ray analysis. An optical band gap of 3.69
eV has been estimated by UV–visible spectrophotometry
Perovskite-Structured PbTiO<sub>3</sub> Thin Films Grown from a Single-Source Precursor
Perovskite-structured
lead titanate thin films have been grown on FTO-coated glass substrates
from a single-source heterometallic molecular complex, [PbTiÂ(μ<sub>2</sub>-O<sub>2</sub>CCF<sub>3</sub>)<sub>4</sub>(THF)<sub>3</sub>(μ<sub>3</sub>-O)]<sub>2</sub> (<b>1</b>), which was
isolated in quantitative yield from the reaction of tetraacetatoleadÂ(IV),
tetrabutoxytitaniumÂ(IV), and trifluoroacetic acid from a tetrahydrofuran
solution. Complex <b>1</b> has been characterized by physicochemical
methods such as melting point, microanalysis, FTIR, <sup>1</sup>H
and <sup>19</sup>F NMR, thermal analysis, and single-crystal X-ray
diffraction (XRD) analysis. Thin films of lead titanate having spherical
particles of various sizes have been grown from <b>1</b> by
aerosol-assisted chemical vapor deposition at 550 °C. The thin
films have been characterized by powder XRD, scanning electron microscopy,
and energy-dispersive X-ray analysis. An optical band gap of 3.69
eV has been estimated by UV–visible spectrophotometry