Structural, spectroscopic, and electrochemical behavior of trans-phenolato cobalt(iii) complexes of asymmetric NN′O ligands as archetypes for metallomesogens

Abstract

In order to understand and predict structural, redox, magnetic, and optical properties of more complex and potentially mesogenic electroactive compounds such as [Co(III)(L(t-BuLC))2]ClO4 (1), five archetypical complexes of general formula [Co(III)(L(RA))2]ClO4, where R = H (2), tert-butyl (3), methoxy (4), nitro (5), and chloro (6), were obtained and studied by means of several spectrometric, spectroscopic, and electrochemical methods. The complexes 2, 4, and 6 were characterized by single-crystal X-ray diffraction, and show the metal center in an approximate D2h symmetry. Experimental results support the fact that the electron donating or withdrawing nature of the phenolate-appended substituents changes dramatically the redox and spectroscopic properties of these compounds. The 3d6 electronic configuration of the metal ion dominates the overall geometry adopted by these compounds with the phenolate rings occupying trans positions to one another. Formation of phenoxyl radicals has been observed for 1, 3, and 6, but irreversible ligand oxidation takes place upon bulk electrolysis. These data were compared to detailed B3LYP/6-31G (d)-level computational calculations and have been used to account for the results observed. A comparison between compound 1 and archetype 3, validates the approach of using archetypical models to study metal-containing soft materials.

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

“…The average area per molecule at collapse (A c ) was obtained by extrapolating the steepest part of the curve down to zero pressure. [3,14] The pyridine head-group of the ligand seems to have interfered little with the packing of the monolayer, and the observed area of [23][24][25] 2 molecule À1 is comparable to the packing reported for a carboxylic acid with an equivalent number of carbon atoms. [40] The formal film collapse happened at 45-50 mN m…”

“…In recent years, our groups have spearheaded systematic research in this area by focusing on a comprehensive approach that encompasses synthesis, [25] modeling, [26] and surface behavior. 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.…”

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.…”

“…[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. Structural rigidity of the ligand takes precedence to the electronic configuration of the metal ion and favors meridional coordination when asymmetric amines and imines are compared.…”

Co(III) and Cu(II) benzimidazole Schiff base complexes: Synthesis, Characterization and DNA binding and cleavage activity

“…The electronic spectra of the Co (III) C1 and C2 give bands around 650 nm. This band is assigned to the transition 1 A 1g → 1 T 2 g, suggesting that there is an octahedral geometry around Co (III) ion 20 . Another band at around 396-438 nm refers to the charge transfer band in all the complexes 21 .…”