Nonlinear Optical and Related Properties of Iron(II) Pentacyanide Complexes with Quaternary Nitrogen Electron Acceptor Units

• Published in: Inorganic chemistry Vol. 48; no. 4; pp. 1370 - 1379
• Main Authors: Coe, Benjamin J, Foxon, Simon P, Harper, Elizabeth C, Raftery, James, Shaw, Rachel, Swanson, Catherine A, Asselberghs, Inge, Clays, Koen, Brunschwig, Bruce S, Fitch, Anthony G
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 16-02-2009
• Subjects: Crystallography, X-Ray; Electrochemical Techniques; Electron Transport; Ferrous Compounds - chemistry; Nitrogen - chemistry; Oxidation-Reduction; Salts - chemistry; Spectrum Analysis
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic801224u

Three new complex salts Na2[FeII(CN)5(L)] [L = N-methyl-4-{E,E-4-(4-pyridyl)buta-1,3-dienyl}pyridinium, N-methyl-4-{E,E,E-6-(4-pyridyl)hexa-1,3,5-trienyl}pyridinium, or N-methyl-1,4-bis-{E-2-(4-pyridyl)ethenyl}] benzene have been prepared. These compounds have been characterized by using various techniques including electronic absorption spectroscopy and cyclic voltammetry, allowing their properties to be compared with those of the known complexes where L = N-methylpyrazinium (Mepyz+), N-methyl-4,4′-bipyridinium, or N-methyl-4-[E-2-(4-pyridyl)ethenyl]pyridinium. Molecular quadratic nonlinear optical (NLO) responses have been determined by using hyper-Rayleigh scattering (HRS) at 1064 nm, and also via Stark (electroabsorption) spectroscopic studies on the intense, visible d → π* metal-to-ligand charge-transfer (MLCT) bands. The MLCT transitions show large red-shifts on moving from aqueous to methanol solutions, and these excitations are associated with relatively large static first hyperpolarizabilities β0. Single crystal X-ray structures of two hydrated materials containing the complex anion [FeII(CN)5(Mepyz+)]2− have been determined, and both of these show some degree of alignment of the constituent complex dipoles.