Archetypical Modeling and Amphiphilic Behavior of Cobalt(II)-Containing Soft-Materials with Asymmetric Tridentate Ligands

Abstract

The stabilization of a bivalent oxidation state in cobalt complexes of phenolate-based asymmetric tridentate ligands with iodo and bromo substituents is studied. The complexes [CoII(LIA)2].2CH3OH (1) and [CoII(LBrA)2].CH3OH (2) were characterized by means of several spectroscopic and spectrometric techniques. The molecular structure of 1 was determined by diffractometric analysis and reveals the cobalt(II) ion in a distorted-octahedral geometry. The centrosymmetric metal ion adopts a local D2h symmetry and is surrounded by facially coordinated ligands. Equivalent donor sets in both ligands are trans to each other, and DFT calculations suggest that the fac-trans configuration is favored by a small margin when compared to the fac-cis isomers. Both DFT calculations and EPR spectroscopy agree with a high-spin S=3/2 electronic configuration given by [ag1, b1g1, ag1, b2g2, b3g2]. This oxidation state was indirectly observed by the lack of a ppiphenolate-->dsigma*cobalt(III) charge-transfer band, which is found between 430 and 470 nm for similar cobalt(III) species. On the basis of the geometrical preferences and the oxidation state of archetypical 1 and 2, two metallosurfactants [CoII(LI-ODA)2] (3) and [CoII(LI-NOBA)2].CH2Cl2 (4) were obtained. The redox chemistry of 1-4 is marked by metal- and ligand-centered activity with several follow up processes and film formation on the electrode. Both metallosurfactants exhibit amphiphilic properties and organization, as shown by compression isotherms and Brewster angle microscopy but exhibit dissimilar collapse mechanisms; whereas 3 collapses at constant pressure, 4 exhibits a constant-area collapse. Langmuir-Blodgett films are readily obtained and were characterized by equilibrium contact angle and atomic force microscopy.

On the Effect of Coordination and Protonation Preferences in the Amphiphilic Behavior of Metallosurfactants with Asymmetric Headgroups

“…Similarly, the archetypical ligands were synthesized with 80-85 % yields following literature procedures [17,20,21] and characterized by means of ESI mass spectrometry, 1 H NMR, and infrared spectroscopy. ticularly visible at low cone voltages.…”

“…Nevertheless, the small body of work available on the isolation and air/water interface behavior of metallosurfactant precursors still poses a major drawback to the approach. [13,14] At the forefront of this area, our group has focused on synthetic, modeling, and surface protocols involving the incorporation of magnetic µ-oxo-Cu 4 clusters in LangmuirBlodgett films, [15,16] the observation of distinctive collapse mechanisms on cobalt(II) films, [17] and the design of redoxactive copper-containing amphiphiles. [18,19] In a series of studies with iron(III), [20] cobalt(II/III), [21] and gallium-(III) [22] we have demonstrated that structural and electronic effects can determine the preferential geometry of redoxactive asymmetric NNЈO ligands in [ML 2 ] metallosurfactants.…”

Interfacial Behavior and Film Patterning of Redox‐Active Cationic Copper(II)‐Containing Surfactants

“…We have demonstrated the feasibility of Langmuir-Blodgett (LB) films with magnetic copper(II) clusters, [27] the redox-state control and dependence of a collapse mechanism on cobalt(II) films, [28] and the factor that determines the delicate equilibrium between redox activity and amphiphilicity in copper/phenoxyl species. [29] Herein, we present an in-depth investigation of the properties of novel single-tail cationic copper(II)-containing surfactants with the ligands L PyC 18 , L PyC 16 , L PyC 14 , and L PyC 10 , in which Py = pyridine and C n indicates the alkyl chain length.…”

“…Overall, the C 16 species start organizing at lower area per molecule values and collapse at slightly lower pressures than their C 18 counterparts, which thus reflects the influence of the chain length. In contrast to 1 and 4, species 2 and 5 display similar A c values of [26][27][28] 2 at collapse, with 5 showing a steeper slope. The reported collapse pressures for 1, 2, 4, and 5 are significantly greater than those observed for other metal-surfactant complexes.…”

A mechanistic approach for the DNA binding of chiral enantiomeric L‐ and D‐tryptophan‐derived metal complexes of 1,2‐DACH: Cleavage and antitumor activity

“…Therefore, the fact that we have observed a signal indicates the presence of Co(II) ions. 30 The EPR spectra of 1(a and b) interpreted in terms of g values displays g II 5 2.9431 and g \ 5 2.548, characteristic of pseudo-octahedral cobalt complexes. No hyperfine splitting with the cobalt nucleus (I 5 7/2) was observed, which suggests that the exchange interaction between Co(II) ions is large enough to collapse this interaction into a single line.…”