Theoretical Study on Second Hyperpolarizabilities of Singlet Diradical Square Planar Nickel Complexes Involving o-Semiquinonato Type Ligands

Abstract

Hybrid density functional theory method is applied for investigating the diradical character dependence of the second hyperpolarizability (gamma) of square planar nickel complexes involving several types of bidentate ligands [o-C6H4XY, where X = Y = O, NH, S, Se, and PH as well as (X, Y) = (NH, NH2) and (S, NH2)]. It is found that, as a function of the donor atoms, the diradical character of these complexes varies from 0.0 to 0.884 and is associated with substantial variations of gamma ranging from 14 x 10(3) to 819 x 10(3) au. In particular, the largest gamma values are associated with intermediate diradical characters in good agreement with the structure-property relationship obtained for pure hydrocarbon systems. Increasing the electronegativity of the X and Y donor groups of the ligands leads to larger diradical characters as a result of the enhancement of the double bond nature of the C=X(Y) bonds, which further stabilizes the diradicals on both-end benzene rings. This demonstrates that the electronegativities of the donor atoms of the ligands become a tuning parameter of the diradical character and then of the gamma values of these complexes.

Synthesis and non-linear optical properties of some novel nickel derivatives

“…10 for the case of the isolated Ni compound. It is observed that the intramolecular charge transfer (p-> p*) over the ligands (S,C), describes the first and strong UV-Vis transition, similar to what was found for other studied metal complexes [12,50,55]. The metal d orbital (d xz ) contributes to LUMO to a minor extent only [55].…”

“…Two functionals were used in the calculations: (i) the PW91LYP using the aug-cc-pVTZ basis set for Ni,C,S,H,O atoms [37], and (ii) the BHandHLYP [38], employing the 6-31G* basis set for C,S,H,O [39], while for Ni a quasirelativistic effective core pseudopotential was employed (ECP28MWB (SDD) [40]). The second functional has been proven to provide reliable values of the second hyperpolarizability for a series of Ni compounds [12].…”

“…Several DFT computations have been performed by employing the broken symmetry solution. The former approach is known to provide reasonable NLO properties [12], and especially second hyperpolarizabilities, to systems which are characterized as singlet diradicals like the synthesized metal derivatives of the present study [13]. We have also computed the UVVis spectrum of the metal derivatives, by employing DFT theory, in order to describe the nature of the observed transitions, which govern the NLO response of the considered derivatives.…”

“…11.96 e a The B3LYP/SDD optimized geometry was employed to all calculations. b The values were calculated with the UHF/6-31G** method [12] (dddt) 2 ) = 0.24 Â 10 À23 esu. (RPW91LYP/aug-cc-pvTZ).…”

“…In order to check the diradical character of the considered compounds, we employ the parameter y i [12]. The value of this parameter is given for the considered singlet diradical systems in Table 8.…”