Synthesis, redox properties, and Langmuir monolayer formation of selected <i>3d</i>- and <i>4d</i>- metalloamphiphiles
Transition metals containing amphiphilic compounds integrate various geometric, electronic, magnetic, and electrochemical properties together with the film forming properties. These compounds thereby find potential towards the fabrication of responsive films. This dissertation confers the synthesis and analysis of film forming properties of various redox-active metalloamphiphiles. Two new azido and thiocyanto bridged copper-based amphiphiles were synthesized and characterized by IR, UV-visible, and EPR spectroscopies, mass spectrometry, cyclic voltammetry, and elemental analysis. The redox studies show that both these complexes exhibit redox reversibility with only the azido bridged complex showing good redox cycling of about 50 times with minimal decomposition of less than 30 mV. The UV-visible studies using coordinating solvent suggest that monomer/dimer equilibria might happen at the air/water interface. The LB studies show that the monolayer stability is maintained up to a pressure of ca. 49 mN/m when collapse occurs. The IRRAS spectra suggest high order of the deposited film.
The synthesis and characterization a series of single-tailed copper(II)-containing surfactants of the type [CuII(LPY18)X2] with varying coligands (X) was also studied. The complexes [CuII(L PY18)(OAc)2], [CuII(LPY18)(OBz) 2], [CuII(LPY18)(acac)Br], [Cu II(LPY18)(dbm)Br], [CuII(LPY18 )(Ox)], and [CuII(LPY18)(1,10-phen)Cl]PF 6 were synthesized, isolated, and characterized. The redox characteristics change depending on the nature of the coligands without compromising the amphiphilic behavior of the complexes. The monodentate coligands (acetate and benzoate) containing complexes exhibit a quasi-reversible CuII→Cu I couple with a potential of about −900 mV whereas the bidentate coligands such as acetylacetonate, dibenzoyl methanate, and oxalate offered irreversible multiple processes. The phenanthroline containing complex exhibited the best reversibility together with excellent cyclability. The Langmuir monolayer isotherm indicates that the films of these complexes are stable up to a pressure of about 45 mN/m. BAM studies showed intricate variations in film topology. The IRRAS studies on selected complexes indicate the presence of well-packed condensed monolayer on the surface of the substrate.
Three octahedral amphiphilic metal complexes of bivalent iron, cobalt, and ruthenium were also synthesized and characterized. The iron containing complex do not show good redox behavior however, the cobalt complex shows a quasi-reversible ligand based process at E1/2 = −1379 mV and the ruthenium complex shows two ligand related processes at E1/2 = −1609 and −2050 mV and RuII/Ru III couple at 600 mV. All the complexes reveal excellent film formation properties. The IRRAS studies display the presence the CH stretching bands at around 2850–2925 cm−1.
We also report on the synthesis and characterization of various copper and nickel containing complexes containing phenolate based ligands with varying substitutents. The redox studies on the nickel complexes reveal quasi-reversible ligand based process and the copper complexes show good reversibility of the copper(II)-based process. However, these amphiphilic complexes showed a compromising behavior at the air/water interface with a maximum collapse pressure of 28 mN/m.
We have also presented the Langmuir-Blodgett film formation studies on various bimetallic and tetrametallic copper complexes and the effect of changes in the subphase on the film formation.
A new family of pyridyl- and phenolato-containing amphiphiles such as [(LPY18I)RuII(bpy)2](PF6) 2, [(LPY18A)RuII(bpy)2](PF 6)2, [(LPhBuI)RuII(bpy) 2](PF6), and [(LPhClI)RuII(bpy) 2](PF6) were also described. The capability of these species as precursors for photo-responsive Langmuir-Blodgett films was evaluated. These complexes are surface active and are strong candidates for the formation of monolayer films, as characterized by compression isotherms and Brewster angle microscopy. Relative solubility in water for the ruthenium pyridyl complexes requires the presence of an aqueous NaCl subphase for proper film formation.
We have also reported on the tetrametallic complex [FeII(Fe IIIL2)3](PF6)2 of discoid topology. To the best of our knowledge, this is the first species in which the presence of tert-butyl groups concurrently imposes redox activity and surfactancy. This result points that a modular approach can be used to develop redox-active homo and heterometallic film precursors of discoid topology.
0794: Materials science