Temperature effect on the optical spectra of Iron(III) metal complexes exhibiting spin crossover and potential nonlinear optical properties

Issue title: Atomic and molecular nonlinear optics: Theory, Experiment and Computation A homage to the pioneering work of Stanisław Kielich (1925-1993)

Guest editors: G. Maroulis, T. Bancewicz, B. Champagne and A.D. Buckingham

Article type: Research Article

Authors: Lamère, Jean François^a | Peyrou, Viviane^a | Sasaki, Isabelle^a | Lacroix, Pascal G.^{a; *} | Vendier, Laure^a | Boillot, Marie Laure^b

Affiliations: [a] CNRS; LCC (Laboratoire de Chimie de Coordination); 205 route de Narbonne, F-31077 Toulouse, France | [b] ICMMO, Equipe de Chimie Inorganique, (UMR 8182), Univ Paris-Sud, 91405 Orsay, France

Correspondence: [*] Corresponding author. Tel.: +33 561333188; Fax: +33 561553003; E-mail: [email protected].

Abstract: Two complexes of formula [FeIII(salten)(DEAS)](BPh4) and [FeIII(salten)(MPS)](BPh4) are reported in which H2 salten is the 4-azaheptamethylene-1,7-bis(salicylideneiminate) quinquadentate Schiff base ligand, DEAS is 4'-diethylamino-stilbazole, and MPS is 4'-[2-(methoxymethyl)pyrrolidinyl]-stilbazole. Both complexes exhibit a partial S=5/2 → 1/2 spin crossover behaviour on cooling down to low temperature. Additionally, DEAS exhibits potential nonlinear optical (NLO) properties in relation to an intense π-π* charge transfer transition between the amine and the pyridine moieties. The temperature dependence of the optical spectra of [FeIII(salten)(DEAS)]+ is compared to that of 4'-diethylamino-1-methylstilbazolium (DEAMS+), a cation related to [FeIII(salten)(DEAS)]+, in which the NLO active DEAS ligand is linked to a methyl instead of an iron complex, and therefore exhibits no magnetic behaviour. The occurrence of a red shift upon cooling down is discussed in relation with the spin equilibrium, on the basis of the ZINDO calculated spectra. A similar shift is observed between [FeIII(salten)(mepepy)]+ complex (mepepy=1-(pyridin-4-yl)-2-(N-methylpyrrol-2-yl)-ethane) and Me-mepepy+, N-methylated form of mepepy. The potential effect of these behaviours on the NLO properties is discussed, in a perspective of molecular materials with interacting electronic capabilities.

Keywords: Spin crossover, nonlinear optics, ZINDO, semi-empirical methods, UV-vis spectra

DOI: 10.3233/JCM-2010-0332

Journal: Journal of Computational Methods in Sciences and Engineering, vol. 10, no. 3-6, pp. 447-463, 2010