Synthesis of organometallic Ru(II) and Fe(II) complexes containing fused rings hemi-helical ligands as chromophores. Evaluation of non-linear optical properties by HRS M. Helena Garcia a, * , Pedro Florindo a , M. Fátima M. Piedade b , M. Teresa Duarte b , M. Paula Robalo b,c , Jürgen Heck d , Christian Wittenburg d , Jan Holtmann d , Emanuela Licandro e a Centro de Ciências Moleculares e Materiais, Faculdade de Ciências da Universidade de Lisboa, Edificio C8, Campo Grande, 1749-016 Lisboa, Portugal b Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal c Departamento de Engenharia Química, Instituto Superior de Engenharia de Lisboa, Rua Conselheiro Emídio Navarro, 1, 1959-007 Lisboa, Portugal d Institut für Anorganische und Angewandte Chemie, Universität Hamburg, Martin-Luther- King-Platz 6, D-20146 Hamburg, Germany e Dipartimento de Chimica Organica e Industriale, Università degli Studi di Milano, Via C. Golgi, 19, 20133 Milano, Italy article info Article history: Received 4 April 2008 Received in revised form 7 May 2008 Accepted 7 May 2008 Available online 31 July 2008 Dedicated to the memory of Professor Alberto Romão Dias. Keywords: Ruthenium(II) Iron(II) Benzodithiophene Nonlinear optics Hyper-Rayleigh scattering (HRS) Monocyclopentadienyl complexes abstract A new family of three-legged piano stool structured organometallic compounds containing the fragment g 5 -cyclopentadienyl-ruthenium(II)/iron(II) has been synthesized to evaluate the existence of electronic metal to ligand charge transfer upon coordination of the novel benzodithiophene ligands (BDT), benzo[1,2-b;4,3-b 0 ]dithiophen-2-carbonitrile (L1) and benzo[1,2-b;4,3-b 0 ]dithiophen-2 0 nitro-2-carboni- trile (L2). All the compounds were characterized by 1 H, 13 C, 31 P NMR, IR and UV–Vis. spectroscopies and their electrochemistry studied by cyclic voltammetry. The X-ray structures of [Ru(g 5 -C 5 H 5 )(PPh 3 ) 2 - (NCC 10 H 5 S 2 )][PF 6 ](1Ru), [Ru(g 5 -C 5 H 5 )(PPh 3 ) 2 (NCC 10 H 5 S 2 )][CF 3 SO 3 ](1 0 Ru), [Ru(g 5 -C 5 H 5 )(DPPE)(NCC 10 - H 5 S 2 )][PF 6 ] 2Ru and [Fe(g 5 -C 5 H 5 )(DPPE)(NCC 10 H 5 S 2 )][PF 6 ](2Fe) were determined by X-ray diffraction showing centric crystallization on groups P  1 and P2 1 /n, respectively. Quadratic hyperpolarizabilities (b) of some of the complexes (2Fe, 2Ru and 3Fe) have been determined by hyper-Rayleigh scattering (HRS) measurements at a fundamental wavelength of 1500 nm, to minimize the probability of fluorescence due to two-photon absorption and to reduce the effect of resonance enhancement, in order to estimate static b values. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction The search for new organometallic materials with nonlinear optical (NLO) properties has been an area of considerable interest due to its relevance to optical device technology [1–6]. The high values of first molecular hyperpolarizability (b) found in organometallic compounds has been related to low energy elec- tronic metal-to-ligand or ligand-to-metal charge transfer excita- tions. In addition, this charge transfer energy can be tuned by variation of the metal itself and its oxidation state, ligand environ- ment and coordination geometries in order to optimize the second order NLO response. Significant results have been achieved in push–pull systems in which the metal centre, bonded to a polariz- able organic conjugated backbone (chromophore), acts as an elec- tron releasing or withdrawing group [1–6]. In particular, structures presenting the metal centre and the chromophore in the same plane, have been found of potential interest for second-order opti- cal nonlinearities, due to the charge delocalization through a d metal –p * ligand interaction. This is widely illustrated in the literature by the families of g 5 -monocyclopentadienyl iron and ruthenium molecular materials presenting p-nitrobenzonitriles [7–10], p-nitro- benzoacetylides [11–13], nitrothienylacetylides [14] and thiophene derivatives [15]. Although the first molecular hyperpolarizability of purely organic push–pull molecules increases strongly with the length of the conjugated chain [16,17], this is not the case for the benz- oderivatives, due to the torsion angle between the rings. Neverthe- less, the extension of conjugation turns out effective by insertion of a vinylene unit between two phenyl rings. Yet, extended conju- gated chain in systems based on thiophene rings, is expected to present an improved planarity since the torsion angle between rings can become quite small. In accordance, ab initio calculations [18] suggests that for terthiophene, although the gas-phase structure is not planar, the conformational inter-conversion energy is very low and sensitive to the chemical environment. Also a 0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2008.05.035 * Corresponding author. Tel.: +351 217500972; fax: +351 217500088. E-mail addresses: lena.garcia@ist.utl.pt, i017@alfa.ist.utl.pt (M.H. Garcia). Journal of Organometallic Chemistry 693 (2008) 2987–2999 Contents lists available at ScienceDirect Journal of Organometallic Chemistry journal homepage: www.elsevier.com/locate/jorganchem