Phoenix

A novel chiral coordination polymer, [Cu­(C₆H₅CH­(OH)­COO)­(μ-C₆H₅CH­(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 [Fe₄S₄] and [Fe₂S₂] Clusters Bearing Amide Ligands

Structural conversion of [Fe₄S₄] clusters into [Fe₂S₂] clusters has been suggested to be a fundamental process for some O₂-sensing proteins. While the formation of [Fe₂S₂] clusters from synthetic [Fe₄S₄] clusters has been unprecedented, an all-ferric [Fe₄S₄]⁴⁺ cluster Fe₄S₄{N­(SiMe₃)₂}₄ (<b>1</b>) was found to split in the presence of pyridines, giving [Fe₂S₂] clusters Fe₂S₂­{N­(SiMe₃)₂}₂(L)₂ (<b>2</b>, L = pyridines). The structural conversion between [Fe₄S₄] and [Fe₂S₂] 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 [Fe₂S₂] clusters was also induced by chemical reductions of Fe₂S₂­{N­(SiMe₃)₂}₂(Py)₂ (Py = pyridine), and the resultant [Fe₄S₄] clusters [<b>1</b>]⁻ and [<b>1</b>]^2– were found to split into two [Fe₂S₂] clusters by oxidation with [Cp₂Fe]⁺ in the presence of pyridine

Reduction of C₁ Substrates to Hydrocarbons by the Homometallic Precursor and Synthetic Mimic of the Nitrogenase Cofactor

Solvent-extracted nitrogenase cofactors can reduce C₁ substrates (CN^–, CO and CO₂) to hydrocarbons in reactions driven by a strong reductant, SmI₂ (<i>E</i>^0′ = −1.55 V vs SCE). Here we show that a synthetic [Et₄N]₄[Fe₆S₉(SEt)₂] cluster (designated the Fe₆^RHH-cluster), which mimics the homometallic [Fe₈S₉C] core of the nitrogenase cofactor (designated the L-cluster), is capable of conversion of C₁ 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 C₁ 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 [Fe₄S₄]³⁺ cluster, [Fe₄S₄{N­(SiMe₃)₂}₄]⁻ (<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 [Fe₄S₄(SR)₄]⁻ 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 [Fe₄S₄]^3+/2+ 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⁺ in THF, are significantly more negative than that of [Fe₄S₄(SPh)₄]^−/2– (−0.21 V)