4 research outputs found
Phoenix
A novel chiral coordination polymer, [Cu(C<sub>6</sub>H<sub>5</sub>CH(OH)COO)(μ-C<sub>6</sub>H<sub>5</sub>CH(OH)COO)]
(<b>1</b>-L and <b>1</b>-D), was synthesized through a
reaction of copper
acetate with l-mandelic acid at room temperature. Although
previously reported copper mandelate prepared by hydrothermal reaction
was a centrosymmetric coordination polymer because of the racemization
of mandelic acid, the current coordination polymer shows noncentrosymmetry
and a completely different structure from that previously reported.
The X-ray crystallography for <b>1</b>-L revealed that the copper
center of the compound showed a highly distorted octahedral structure
bridged by a chiral mandelate ligand in the unusual coordination mode
to construct a one-dimensional (1D) zigzag chain structure. These
1D chains interdigitated each other to give a layered structure as
a result of the formation of multiple aromatic interactions and hydrogen
bonds between hydroxyl and carboxylate moieties at mandelate ligands.
The coordination polymer <b>1</b>-L belongs to the noncentrosymmetric
space group of C2 to show piezoelectric properties and second harmonic
generation (SHG) activity
Interconversion between [Fe<sub>4</sub>S<sub>4</sub>] and [Fe<sub>2</sub>S<sub>2</sub>] Clusters Bearing Amide Ligands
Structural conversion
of [Fe<sub>4</sub>S<sub>4</sub>] clusters into [Fe<sub>2</sub>S<sub>2</sub>] clusters has been suggested to be a fundamental process
for some O<sub>2</sub>-sensing proteins. While the formation of [Fe<sub>2</sub>S<sub>2</sub>] clusters from synthetic [Fe<sub>4</sub>S<sub>4</sub>] clusters has been unprecedented, an all-ferric [Fe<sub>4</sub>S<sub>4</sub>]<sup>4+</sup> cluster Fe<sub>4</sub>S<sub>4</sub>{N(SiMe<sub>3</sub>)<sub>2</sub>}<sub>4</sub> (<b>1</b>) was found to split
in the presence of pyridines, giving [Fe<sub>2</sub>S<sub>2</sub>]
clusters Fe<sub>2</sub>S<sub>2</sub>{N(SiMe<sub>3</sub>)<sub>2</sub>}<sub>2</sub>(L)<sub>2</sub> (<b>2</b>, L = pyridines).
The structural conversion between [Fe<sub>4</sub>S<sub>4</sub>] and
[Fe<sub>2</sub>S<sub>2</sub>] clusters appeared to be reversible,
and the thermodynamic parameters for the equilibrium reactions between <b>1</b> + L and <b>2</b> were determined. Assembly of two
[Fe<sub>2</sub>S<sub>2</sub>] clusters was also induced by chemical
reductions of Fe<sub>2</sub>S<sub>2</sub>{N(SiMe<sub>3</sub>)<sub>2</sub>}<sub>2</sub>(Py)<sub>2</sub> (Py = pyridine), and the
resultant [Fe<sub>4</sub>S<sub>4</sub>] clusters [<b>1</b>]<sup>−</sup> and [<b>1</b>]<sup>2–</sup> were found
to split into two [Fe<sub>2</sub>S<sub>2</sub>] clusters by oxidation
with [Cp<sub>2</sub>Fe]<sup>+</sup> in the presence of pyridine
Reduction of C<sub>1</sub> Substrates to Hydrocarbons by the Homometallic Precursor and Synthetic Mimic of the Nitrogenase Cofactor
Solvent-extracted
nitrogenase cofactors can reduce C<sub>1</sub> substrates (CN<sup>–</sup>, CO and CO<sub>2</sub>) to hydrocarbons
in reactions driven by a strong reductant, SmI<sub>2</sub> (<i>E</i><sup>0′</sup> = −1.55 V vs SCE). Here we
show that a synthetic [Et<sub>4</sub>N]<sub>4</sub>[Fe<sub>6</sub>S<sub>9</sub>(SEt)<sub>2</sub>] cluster (designated the Fe<sub>6</sub><sup>RHH</sup>-cluster), which mimics the homometallic [Fe<sub>8</sub>S<sub>9</sub>C] core of the nitrogenase cofactor (designated the
L-cluster), is capable of conversion of C<sub>1</sub> substrates into
hydrocarbons in the same reactions. Comparison of the yields and product
profiles between these homometallic clusters and their heterometallic
counterparts points to possible roles of the heterometal, interstitial
carbide and belt sulfur-bridged iron atoms in catalysis. More importantly,
the observation that a “simplified”, homometallic cofactor
mimic can perform Fischer–Tropsch-like hydrocarbon synthesis
suggests future biotechnological adaptability of nitrogenase-based
biomimetic compounds for recycling C<sub>1</sub> substrates into useful
chemical and fuel products
A Convenient Route to Synthetic Analogues of the Oxidized Form of High-Potential Iron–Sulfur Proteins
An amide-bound [Fe<sub>4</sub>S<sub>4</sub>]<sup>3+</sup> cluster, [Fe<sub>4</sub>S<sub>4</sub>{N(SiMe<sub>3</sub>)<sub>2</sub>}<sub>4</sub>]<sup>−</sup> (<b>1</b>), was found to serve as a convenient precursor for synthetic analogues
of the oxidized form of high-potential iron–sulfur proteins.
Treatment of <b>1</b> with 4 equiv of bulky thiols led to replacement
of the amide ligands with thiolates, giving rise to a series of [Fe<sub>4</sub>S<sub>4</sub>(SR)<sub>4</sub>]<sup>−</sup> clusters
(R = Dmp (<b>2a</b>), Tbt (<b>2b</b>), Eind (<b>2c</b>), Dxp (<b>2d</b>), Dpp (<b>2e</b>); Dmp = 2,6-di(mesityl)phenyl,
Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Eind = 1,1,3,3,5,5,7,7-octaethyl-<i>s</i>-hydrindacen-4-yl, Dxp = 2,6-di(<i>m</i>-xylyl)phenyl,
Dpp = 2,6-diphenylphenyl). These clusters were characterized by the
mass spectrum, the EPR spectrum, and X-ray crystallography. The redox
potentials of the [Fe<sub>4</sub>S<sub>4</sub>]<sup>3+/2+</sup> couple,
−0.82 V (<b>2a</b>), −0.86 V (<b>2b</b>),
−0.84 V (<b>2c</b>), −0.74 V (<b>2d</b>),
and −0.63 V (<b>2e</b>) vs Ag/Ag<sup>+</sup> in THF,
are significantly more negative than that of [Fe<sub>4</sub>S<sub>4</sub>(SPh)<sub>4</sub>]<sup>−/2–</sup> (−0.21
V)