Mössbauer Spectroscopic Characterization of Iron(III)–Polysaccharide Coordination Complexes: Photochemistry, Biological, and Photoresponsive Materials Implications

While polycarboxylates and hydroxyl-acid complexes have long been known to be photoactive, simple carboxylate complexes which lack a significant LMCT band are not typically strongly photoactive. Hence, it was somewhat surprising that a series of reports demonstrated that materials synthesized from iron­(III) and polysaccharides such as alginate (poly­[guluronan-<i>co</i>-mannuronan]) or pectate (poly­[galacturonan]) formed photoresponsive materials that convert from hydrogels to sols under the influence of visible light. These materials have numerous potential applications in areas such as photopatternable materials, materials for controlled drug delivery, and tissue engineering. Despite the near-identity of the functional units in the polysaccharide ligands, the reactivity of iron­(III) hydrogels can depend on the configuration of some chiral centers in the sugar units and in the case of alginate the guluronate to mannuronate block composition, as well as pH. Here, using temperature- and field-dependent transmission Mössbauer spectroscopy, we show that the dominant iron compound detected for both the alginate and pectate gels displays features typical of a polymeric (Fe³⁺O₆) system. The Mössbauer spectra of such systems are strongly dependent on temperature, field, size, and crystallinity, indicative of superparamagnetic relaxation of magnetically ordered nanoparticles. Pectate and alginate hydrogels differ in the size distribution of the iron oxyhydroxy nanoparticles, suggesting that in general smaller nanoparticles are more reactive. Potential biological implications of these results are also discussed

Cyclopentadienide Ligand Cp^C– Possessing Intrinsic Helical Chirality and Its Ferrocene Analogues

The novel chiral cyclopentadiene-type ligand Cp^CH is accessible from dibenzosuberenone in a five-step sequence with overall yields of 64%. NMR spectroscopy as well as DFT calculations prove that the racemization of this compound is slow at room temperature. By deprotonation of Cp^CH and subsequent reaction with appropriate iron­(II) precursors, the novel ferrocene derivatives (Cp^C)₂Fe and (Cp^C)­Fe­(⁴Cp) are accessible in good yields. The latter could structurally be characterized by means of single-crystal X-ray crystallography. Mössbauer spectroscopy proves the ferrocene nature of (Cp^C)₂Fe and (Cp^C)­Fe­(⁴Cp), and electrochemical investigations carried out with (Cp^C)­Fe­(⁴Cp) show that the compound is, as expected, more easily oxidized than ferrocene

Cyclopentadienide Ligand Cp^C– Possessing Intrinsic Helical Chirality and Its Ferrocene Analogues

The novel chiral cyclopentadiene-type ligand Cp^CH is accessible from dibenzosuberenone in a five-step sequence with overall yields of 64%. NMR spectroscopy as well as DFT calculations prove that the racemization of this compound is slow at room temperature. By deprotonation of Cp^CH and subsequent reaction with appropriate iron­(II) precursors, the novel ferrocene derivatives (Cp^C)₂Fe and (Cp^C)­Fe­(⁴Cp) are accessible in good yields. The latter could structurally be characterized by means of single-crystal X-ray crystallography. Mössbauer spectroscopy proves the ferrocene nature of (Cp^C)₂Fe and (Cp^C)­Fe­(⁴Cp), and electrochemical investigations carried out with (Cp^C)­Fe­(⁴Cp) show that the compound is, as expected, more easily oxidized than ferrocene

Cyclopentadienide Ligand Cp^C– Possessing Intrinsic Helical Chirality and Its Ferrocene Analogues

The novel chiral cyclopentadiene-type ligand Cp^CH is accessible from dibenzosuberenone in a five-step sequence with overall yields of 64%. NMR spectroscopy as well as DFT calculations prove that the racemization of this compound is slow at room temperature. By deprotonation of Cp^CH and subsequent reaction with appropriate iron­(II) precursors, the novel ferrocene derivatives (Cp^C)₂Fe and (Cp^C)­Fe­(⁴Cp) are accessible in good yields. The latter could structurally be characterized by means of single-crystal X-ray crystallography. Mössbauer spectroscopy proves the ferrocene nature of (Cp^C)₂Fe and (Cp^C)­Fe­(⁴Cp), and electrochemical investigations carried out with (Cp^C)­Fe­(⁴Cp) show that the compound is, as expected, more easily oxidized than ferrocene

Cyclopentadienide Ligand Cp^C– Possessing Intrinsic Helical Chirality and Its Ferrocene Analogues

The novel chiral cyclopentadiene-type ligand Cp^CH is accessible from dibenzosuberenone in a five-step sequence with overall yields of 64%. NMR spectroscopy as well as DFT calculations prove that the racemization of this compound is slow at room temperature. By deprotonation of Cp^CH and subsequent reaction with appropriate iron­(II) precursors, the novel ferrocene derivatives (Cp^C)₂Fe and (Cp^C)­Fe­(⁴Cp) are accessible in good yields. The latter could structurally be characterized by means of single-crystal X-ray crystallography. Mössbauer spectroscopy proves the ferrocene nature of (Cp^C)₂Fe and (Cp^C)­Fe­(⁴Cp), and electrochemical investigations carried out with (Cp^C)­Fe­(⁴Cp) show that the compound is, as expected, more easily oxidized than ferrocene