Copper(II) Complexes of salen Analogues with Two Differently Substituted (Push−Pull) Salicylaldehyde Moieties. A Study on the Modulation of Electronic Asymmetry and Nonlinear Optical Properties

Abstract

This paper presents some copper(II) complexes of salen analogues in which the two salicylaldehyde moieties carry different (electron donor, D, and acceptor, A) substituents in position 5, producing a push-pull charge asymmetry. The X-ray structures of some compounds show the presence of pairs of stacked molecules with head-to-tail intermolecular associations. The geometries of all complexes have been optimized through density functional theory (DFT) studies, which have shown that a major influence on the coordination bond lengths is given by the presence of the electron acceptor NO2 group. Such an influence operates mainly on the Cu-phenolato bonds: elongation of the Cu-O distance of the 5-nitrosalicylaldehyde moiety, with a concomitant decrease of the other Cu-O distance; the Cu-N bonds are less affected. The D groups have only a minor influence. The nonlinear optical responses, microgBetavec, of some molecules have been determined by EFISH measurements, and the Beta-vec values have been obtained using the DFT-calculated microg values because solubility problems hampered the experimental measurements of microg of some derivatives; the former, however, have been found to be in agreement with the experimental values that could be obtained. Deconvolution of the absorption bands in the near-UV region has allowed recognition of the charge-transfer (CT) transition, assigned to a ligand-to-metal CT (LMCT) by time-dependent DFT computations; we have then used the solvatochromism of this transition to obtain Beta0 and BetaCT values using the two-state model. These values were compared with those obtained by computational studies, which have also allowed evaluation of the influence of the substituents on the directions of microg and Betatot.

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

“…This is in line with the relative mixing between the vacant orbitals of their accepting group and the occupied orbitals of their donor group. The µ values are consistent with those published by Rigamonti et al for A–π–D type compounds bearing the same electron‐withdrawing nitro substituent . Mulliken atomic charges indicate that, as expected, Pd II has a greater positive charge (+1.03) in 4 than does Ni II in complex 3 (+0.46).…”

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

“…This is in line with the relative mixing between the vacant orbitals of their accepting group and the occupied orbitals of their donor group. The µ values are consistent with those published by Rigamonti et al for A–π–D type compounds bearing the same electron‐withdrawing nitro substituent . Mulliken atomic charges indicate that, as expected, Pd II has a greater positive charge (+1.03) in 4 than does Ni II in complex 3 (+0.46).…”

Solid-State Nonlinear Optical Properties of Mononuclear Copper(II) Complexes with Chiral Tridentate and Tetradentate Schiff Base Ligands

“…Owing to the absence of the crystal structure of 2a – c , only hypothesis to compare the molecular properties as described by theoretical calculations with the solid-state NLO data can be formulated in the case of derivatives with unsymmetrically-substituted tetradentate ligands. A possible explanation for the observed diminished χ (2) is the unfavorable alignment of the chromophores, which probably still tend to couple in a head-to-tail fashion, in agreement with previous reports [38,39]. Anyway, the chirality conferred to the final complexes by the diamines prevents perfect alignment, resulting in a small, but non-zero solid-state NLO response.…”

“…Compounds 2a , 2b , and 2c , on the other hand, while having similar dipole moments (13.02, 12.26, and 12.34 D), show increasing values of β tot from 39.7 to 49.2 and 49.6 × 10 −30 cm 5 esu −1 , going from 2a to 2b and 2c , as a consequence of the presence of the donor group OMe in the latter compounds. These values are quite similar to those previously obtained for the [Cu(5-A-5′-D-salen)] analogues with (NO 2 , H) and (NO 2 , OMe) substitutions [38,39], indicating, at the molecular level, the almost irrelevant influence of the ethylene substituents (en vs. dpen vs. chxn) on the electronic properties.…”

Redox‐Active Bis‐Catecholaldimine Cu(II)‐Salen Complex with Hydroxyl Functionality as Cathode Material in Li‐Ion Battery

“…The OCuN bond angles in 1 [O2‐Cu1‐N2, 91.05(9)°; O1‐Cu1‐N1, 91.35(9)°] are also comparable to the literature values reported for the Cu(II) Salen complexes [O2‐Cu1‐N2, 90.98(9)°; O1‐Cu1‐N1, 91.27(8)°] [59, 65].…”

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

“…This is in line with the relative mixing between the vacant orbitals of their accepting group and the occupied orbitals of their donor group. The µ values are consistent with those published by Rigamonti et al for A–π–D type compounds bearing the same electron‐withdrawing nitro substituent . Mulliken atomic charges indicate that, as expected, Pd II has a greater positive charge (+1.03) in 4 than does Ni II in complex 3 (+0.46).…”

Solid-State Nonlinear Optical Properties of Mononuclear Copper(II) Complexes with Chiral Tridentate and Tetradentate Schiff Base Ligands

“…Owing to the absence of the crystal structure of 2a – c , only hypothesis to compare the molecular properties as described by theoretical calculations with the solid-state NLO data can be formulated in the case of derivatives with unsymmetrically-substituted tetradentate ligands. A possible explanation for the observed diminished χ (2) is the unfavorable alignment of the chromophores, which probably still tend to couple in a head-to-tail fashion, in agreement with previous reports [38,39]. Anyway, the chirality conferred to the final complexes by the diamines prevents perfect alignment, resulting in a small, but non-zero solid-state NLO response.…”

“…Compounds 2a , 2b , and 2c , on the other hand, while having similar dipole moments (13.02, 12.26, and 12.34 D), show increasing values of β tot from 39.7 to 49.2 and 49.6 × 10 −30 cm 5 esu −1 , going from 2a to 2b and 2c , as a consequence of the presence of the donor group OMe in the latter compounds. These values are quite similar to those previously obtained for the [Cu(5-A-5′-D-salen)] analogues with (NO 2 , H) and (NO 2 , OMe) substitutions [38,39], indicating, at the molecular level, the almost irrelevant influence of the ethylene substituents (en vs. dpen vs. chxn) on the electronic properties.…”

Redox‐Active Bis‐Catecholaldimine Cu(II)‐Salen Complex with Hydroxyl Functionality as Cathode Material in Li‐Ion Battery

“…The OCuN bond angles in 1 [O2‐Cu1‐N2, 91.05(9)°; O1‐Cu1‐N1, 91.35(9)°] are also comparable to the literature values reported for the Cu(II) Salen complexes [O2‐Cu1‐N2, 90.98(9)°; O1‐Cu1‐N1, 91.27(8)°] [59, 65].…”

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

“…This is in line with the relative mixing between the vacant orbitals of their accepting group and the occupied orbitals of their donor group. The µ values are consistent with those published by Rigamonti et al for A–π–D type compounds bearing the same electron‐withdrawing nitro substituent . Mulliken atomic charges indicate that, as expected, Pd II has a greater positive charge (+1.03) in 4 than does Ni II in complex 3 (+0.46).…”

Solid-State Nonlinear Optical Properties of Mononuclear Copper(II) Complexes with Chiral Tridentate and Tetradentate Schiff Base Ligands

“…Owing to the absence of the crystal structure of 2a – c , only hypothesis to compare the molecular properties as described by theoretical calculations with the solid-state NLO data can be formulated in the case of derivatives with unsymmetrically-substituted tetradentate ligands. A possible explanation for the observed diminished χ (2) is the unfavorable alignment of the chromophores, which probably still tend to couple in a head-to-tail fashion, in agreement with previous reports [38,39]. Anyway, the chirality conferred to the final complexes by the diamines prevents perfect alignment, resulting in a small, but non-zero solid-state NLO response.…”

“…Compounds 2a , 2b , and 2c , on the other hand, while having similar dipole moments (13.02, 12.26, and 12.34 D), show increasing values of β tot from 39.7 to 49.2 and 49.6 × 10 −30 cm 5 esu −1 , going from 2a to 2b and 2c , as a consequence of the presence of the donor group OMe in the latter compounds. These values are quite similar to those previously obtained for the [Cu(5-A-5′-D-salen)] analogues with (NO 2 , H) and (NO 2 , OMe) substitutions [38,39], indicating, at the molecular level, the almost irrelevant influence of the ethylene substituents (en vs. dpen vs. chxn) on the electronic properties.…”

Redox‐Active Bis‐Catecholaldimine Cu(II)‐Salen Complex with Hydroxyl Functionality as Cathode Material in Li‐Ion Battery

“…The OCuN bond angles in 1 [O2‐Cu1‐N2, 91.05(9)°; O1‐Cu1‐N1, 91.35(9)°] are also comparable to the literature values reported for the Cu(II) Salen complexes [O2‐Cu1‐N2, 90.98(9)°; O1‐Cu1‐N1, 91.27(8)°] [59, 65].…”