Synthesis and Second-Order Nonlinear Optical Properties of New Copper(II), Nickel(II), and Zinc(II) Schiff-Base Complexes. Toward a Role of Inorganic Chromophores for Second Harmonic Generation

Abstract

A new Schiff-base ligand based on the condensation of diaminomaleonitrile and 4-(diethylamino)salicylaldehyde is reported with its copper, nickel, and zinc complexes. Their second-order nonlinear optical properties are investigated by electric field induced second harmonic (EFISH) and ZINDO quantum-chemical calculations to probe the role of the metal center in the nonlinearity. All the complexes exhibit a second-order nonlinear response that is larger than that of the ligand with an hyperpolarizability (β) value of 400 (±100) 10-30 cm5 esu-1 for the zinc derivative at 1.34 μm. Theoretical calculations indicate that the two-level model is inadequate to describe the nonlinearity in such systems.

Photoisomerization of a Maleonitrile‐Type Salen Schiff Base and Its Application in Fine‐Tuning Infinite Coordination Polymers

“…Due to the syn addition depicted in Scheme 1, conventional wisdom leads us to propose such a Schiff base to be originally in the Z configuration, similar to most salen ligands reported. [8,9] To our surprise, however, as shown in Figure 1, the X-ray structural analysis unambiguously revealed the E configuration, in which one 4-(di-p-tolylamino)-2-(iminomethyl)phenol wing is rotated around the maleonitrile C=C bond and spatially aligned in a trans orientation with respect to the other. Except for the di-p-tolylamino segments, the main molecular skeleton is in a planar configuration, as indicated by the dihedral angle of about 08 between the C11-C6-C7 and C11A-C6A-C7A planes.…”

“…Interestingly, most metal complexes coordinated by 1Z-analogous salen-type ligands, that is, with D-A-D arrangement, have been reported to have the Z configuration. [8,9] Thus, our finding of photoinduced Z!E isomerization of a Z-configured maleonitrile salen Schiff base may pave a new avenue in chemistry. For example, on metal coordination, the two forms might show different catalytic activities for asymmetric reactions.…”

“…The synthetic route seems to be straightforward, and salen compound 1 with Z configuration with regard to the maleonitrile C=C double bond (1Z, see Figure S1 in the Supporting Information) should be obtained, similar to numerous reports on salen-type ligands. [8,9] Herein we explore a previously unrecognized feature, that is, facile photoisomerization about the maleonitrile C=C double bond of 1Z in the excited state, forming the 1E isomer. To further explore the differences in coordination chemistry between E and Z conformers, we then strategically designed a derivative of 1, namely, N,N'-dicyanoethenebis(salicylideneimine) dicarboxylic acid (2, Scheme 1), which shares the same core moiety as 1 but has additional carboxyl functional groups.…”

“…[20,21] Because of their appropriate coordinating functionalities (COOH), we propose that 2Z (2E) with its intrinsic structure-building motif would be a suitable template to demonstrate as well as to differentiate maleonitrile E/Z conformers leading to different coordination polymers with transition metal ions as nodes. As depicted in Scheme 1, a condensation process [8,9] involving cis-diaminomaleonitrile and 3-formyl-4-hydroxybenzoic acid [22] in methanol afforded 2Z by syn addition, as evidenced by the 1 H NMR spectrum (Figure 7 A, see Experimental Section for further characterization). Compound 2Z exhibits an S 0 !S 1 absorption maximum at 490 nm in dimethyl sulfoxide (DMSO).…”

Synthesis, structures and antimicrobial activities of nickel(II) and zinc(II) diaminomaleonitrile-based complexes

“…The absence of an OH stretching vibration suggests that the O phenolic atoms of the ligands are deprotonated and participate in coordination to the nickel and zinc atoms [21]. The symmetric diimine nature of the complexes is proven by the single band observed in the range of 2209-2225 cm −1 assigned to the (C≡N) stretching vibration, contrary to two bands observed in monoimine compounds [22]. The absorption bands in the range of 735-754 cm −1 and 412-418 cm −1 in the metal complexes are assigned to stretching modes of the M-N and M-O bonds, respectively [23].…”