Jean René Hamon

Synthesis, spectral, structural, second-order nonlinear optical properties and theoretical studies on new organometallic donor-acceptor substituted nickel(II) and copper(II) unsymmetrical Schiff-base complexes.

The synthesis, spectroscopic and structural characterization, linear and nonlinear optical properties, as well as the electrochemical behavior of a series of robust neutral binuclear M[Fc-C(O)CH=C(CH(3))N-X-N=CH-(2-O,5-R-C(6)H(3))] (M = Ni (4), Cu (5), X = o-C(6)H(4), R = H; M = Ni (9), X = CH(2)CH(2), R = OH), and their corresponding ionic trinuclear [M{Fc-C(O)CH=C(CH(3))N-X-N=CH-(eta(6)-2-O,5-R-C(6)H(3))RuCp*}][PF(6)] (6, 7, 10), M[ONNO]-type unsymmetrical Salophen and salen complexes featuring ferrocenyl (Fc) donor and the mixed sandwich acceptor [Cp*Ru(eta(6)- salicylidene)](+) as a push-pull moiety are reported in this paper (Fc = CpFe(eta(5)-C(5)H(4)); Cp = eta(5)-C(5)H(5); Cp* = eta(5)-C(5)Me(5)). The single-crystal X-ray structure of the bimetallic iron-nickel derivative 4 indicates a bowed structure of the unsymmetrical Schiff base skeleton. The Ni(II) ion is tetracoordinated in a square planar environment, with two nitrogen atoms and two oxygen atoms as donors. The new metalloligand [Fc-C(O)CH=C(CH(3))N(H)CH(2)CH(2)N=CH-(2,5-(OH)(2)C(6)H(3))] (8) obtained from the Schiff base condensation of 2,5-dihydroxobenzaldehyde with the half-unit precursor, Fc-C(O)CH=C(CH(3))N(H)CH(2)CH(2)NH(2) (2), is reported with its crystal structure showing partial delocalization of the heteroconjugated [O-C-C-C-N] frameworks with a dihedral angle between the respective planes of 60.76 degrees. Second order nonlinear optical (NLO) measurements were achieved using the Harmonic Light Scattering technique to probe the role of the M[ONNO] chromophores and of the pi-complexation of the salicylidene ring in the nonlinearity. All the complexes exhibit a second-order nonlinear response increasing with the nuclearity, the hyperpolarizability (beta) value of the trinuclear complex 10 being 1.5 time larger than that of the metalloligand 8 (beta = 155 x 10(-30) esu). A rationalization of the structural, electronic, and redox properties of the title compounds is provided, based on a theoretical investigation at the density functional theory (DFT) level. Their UV-visible spectra has been assigned with the help of time-dependent (TD) DFT calculations. They are dominated by LMCT, MLCT, and pi-pi* transitions.

New copper(II)-centered complexes with organometallic donor–acceptor substituted unsymmetrical Schiff base ligands

The synthesis and full characterization using various spectroscopic techniques and single-crystal X-ray diffraction analysis of a family of three robust copper(II)-centered complexes with organometallic donor–acceptor substituted unsymmetrical Schiff base ligands, namely, the binuclear derivatives Cu[Fc–C(O)CHC(CH3)N–X–NCH-(2-O,5-Br–C6H3)] (3: X = o-C6H4, 4: X = CH2CH2), and the corresponding ionic trinuclear counterpart of 4, [Cu{Fc–C(O)CHC(CH3)N–CH2CH2–NCH-(η6-2-O,5-Br–C6H3)RuCp*}][PF6] (5) (Fc = (η5-C5H5)Fe(η5-C5H4), Cp* = η5-C5Me5), have been explored. Single crystal X-ray diffraction analysis of complex 3 indicates a bowed structure of the unsymmetrical Schiff base scaffold. The Cu2+ ion is tetracoordinated in a square planar environment, with two nitrogen atoms and two oxygen atoms as donors. The EPR spectra of solid trinuclear complexes 5 and 7 (unsubstituted salicylidene ring and X = o-C6H4) at low temperature (68 K) consisted of fine-structure transitions (ΔMs = ±1) with zero-field splitting (ZFS) values of 0.0458 and 0.0415 cm−1, respectively, and a half-field signal (ΔMs = ±2) at ca. 1600 G, suggesting the formation of dimeric species (S = 1). In those dimers, Cu–Cu distances of 3.97 and 4.14 A, respectively, are computed from ZFS terms. The variable-temperature (2–300 K) magnetic susceptibilities of powdered samples of 5 and 7 have been measured, and an intermolecular antiferromagnetic interaction with exchange couplings of J = −1.05 and −0.65 cm−1, respectively, were found. The electrochemical behavior of both the neutral binuclear and ionic trinuclear compounds was investigated by cyclic voltammetry. Notably, the ability of the copper Schiff base core to transmit electronic effects between the two organometallic termini has been demonstrated by the observed anodic shift of the reversible voltammetric signal ascribed to the FeII/FeIII couple of the ferrocenyl donor fragment.