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

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 pπphenolate → dσ*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.