Side‐Chain Metallopolymers Containing Second‐Order NLO‐Active Bimetallic NiII and PdII Schiff‐Base Complexes: Syntheses, Structures, Electrochemical and Computational Studies

Abstract

Unsymmetric Schiff‐base metalloligand precursor 2 is synthesized by condensation of phenol‐functionalized ferrocenylenaminone 1 with 2‐hydroxy‐5‐nitrobenzaldehyde. Heterobimetallic complexes 3 and 4 result from the N2O2‐tetradentate coordination of NiII and PdII metal ions with the doubly deprotonated form of 2, respectively. Linking 3 and 4 to polyacrylic acid through an esterification reaction leads to the formation of the corresponding side‐chain metallopolymers 5 and 6. The new compounds were fully characterized (IR, UV/Vis, NMR, MS, CV, SEC) and structures of 2–4 unequivocally determined by single‐crystal X‐ray diffraction techniques. Decomposition temperatures higher than 250 °C were found by DSC and TGA techniques for 3–6. Harmonic light scattering measurements showed that compounds 2–5 exhibit rather high second‐order nonlinear responses, between 200 × 10–30 and 970 × 10–30 esu, with the hyperpolarizability β1.91 value increasing significantly on passing from NiII complex 3 to its respective metallopolymer 5. The structural and electronic properties of 2–4 are analyzed by DFT and TD‐DFT calculations.

Pentacoordinated Chloro-Iron(III) Complexes with Unsymmetrically Substituted N2O2 Quadridentate Schiff-Base Ligands: Syntheses, Structures, Magnetic and Redox Properties

“…The amino and phenolic proton signals were seen at 13.05 and 13.71 ppm, respectively. Such deshielded resonances are in accordance with intramolecular hydrogen bonding of the amino proton with the carbonyl oxygen atom and of the hydroxyl proton with the imine nitrogen atom, thus closing, in both cases, a pseudo six-membered heterocycle (Scheme 1) [34,35,39,40]. The singlet resonance of the methine proton at 5.94 ppm testified the tautomeric keto-enamine form of 2.…”

“…The shape and position of these bands are due to the two intramolecular N-H···O and O-H···N hydrogen bonds (see drawing of 2 in Scheme 1) [34,35]. Strong bands are also observed in the 1614-1584 cm −1 region and are attributed to the characteristic ν(C …”

“…Lastly, the enaminone and salicylaldimine planes rotate by 69.0(1)° and 9.8(1)°, respectively, with respect to that of the o-diazophenylene spacer, while the nitro group is virtually coplanar with the salicylidene ring with a dihedral angle of 2.7(4)°. The potentially tetradentate acyclic ligand 2 exists as the Z-s-Z conformational form [34,35] in the enaminone part of the molecule ( Figure 1) whose plane is almost coplanar with that of the 4-fluorophenyl substituent, making a dihedral angle of 6.3(1) • . The structure also reveals two intramolecular hydrogen bonds that close two pseudo-six-membered rings through the resonant ···O=C-C=C-NH··· fragment [42], with alternating double, single, double and single bonds between the vicinal O, C and N sp 2 -hybridized atoms ( Table 1).…”

Why is Ferrocene so Exceptional?

“…Ferrocenes such as the seminal example of cis ‐1‐ferrocenyl‐2‐(4‐nitrophenyl)ethylene (Figure , left) were found by Green's group, followed by other groups, to show nonlinear optical (NLO) properties, with applications in optical signal processing such as the frequency doubling of laser light.…”

“…It turned out that both the reduction reactions and the organic connectors had a significant influence on the 4,4′‐bipyridinium system . The groups of Hamon, Saillard, Carrillo, Manzur, and Ledoux‐Rak developed another remarkable series of molecular systems in which ferrocene is conjugated with Schiff bases; excellent NLO properties were disclosed . The largest quadratic hyperpolarizability value (970 × 10 –30 esu) was determined for palladium‐containing dimetallic ferrocene Schiff‐base species .…”