title: 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.
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Fukui
authors.forename: Ryohei
authors.initials: R
authors.lastname: Kishi
authors.forename: Takuya
authors.initials: T
authors.lastname: Minami
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nagai
authors.forename: Hideaki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Takashi
authors.initials: T
authors.lastname: Kubo
authors.forename: Kenji
authors.initials: K
authors.lastname: Kamada
authors.forename: Koji
authors.initials: K
authors.lastname: Ohta
authors.forename: Benoît
authors.initials: B
authors.lastname: Champagne
authors.forename: Edith
authors.initials: E
authors.lastname: Botek
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Nakano
mesh_terms: D000465:Algorithms; D005609:Free Radicals / Q000737:chemistry*; D008024:Ligands; D008962:Models, Theoretical; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D011809:Quinones / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D008024:Ligands; D009942:Organometallic Compounds; D011809:Quinones; D009532:Nickel