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Novel bis(arene)metal-containing polyacrylonitrile materials have been prepared by the polycyanoethylation reaction between acrylonitrile and (arene) 2 M (M = Cr or V; arene = PhH, C 6 H 4 Et 2 or mesitylene) in the absence of solvent. The resulting star-shaped molecules consist of a central (arene) 2 M species with up to four polyacrylonitrile arms covalently bonded to the arene ligands. The materials are readily soluble and films can be cast from solutions in acetonitrile. The IR and solid state 13 C NMR spectra (or EPR spectrum for the oxidized chromium-containing polymer) are consistent with the presence of a metal-arene bond and confirm the persistence of the sandwich structure. The properties of the thermolysed materials are consistent with the formation of conjugated naphthyridine-type structures. The value of |n 2 | determined by the degenerate fourwave mixing technique at 1064 nm with a 6 ns pulse duration for a solution in conc. H 2 SO 4 (1 g l À1 ) of the chromium-containing polymer pyrolysed at 350°C was found to be 0.8 Â 10 À13 cm 2 W À1 corresponding to |Re w (3) | = 0.4 Â 10 À11 esu.There is current interest in soluble polymers containing transition metals because of the requirements for advanced materials in molecular electronics, electro-or magneto-optics and catalytical processes. We expect that polymers containing CN groups and having transition metal sandwich complexes in their macrochains should be promising precursors of organometallic metal-containing nanomaterials with interesting magnetic, optical and perhaps magneto-optical properties following chemical, photochemical or thermal treatment. Miller and co-workers have shown that such materials can be formed by the reaction between bis-benzenevanadium and tetracyanoethylene, which gives rise to a high-temperature ferromagnet. 1,2 Similarly, high temperature ferro-and ferri-magnetic behaviour has been observed for cyanometallate (Prussian blue type) compounds, such as mixed valence chromium cyanides, with excellent photochromic properties. 3 The present report focuses on the synthesis and the characterization of new polymer materials based on polyacrylonitrile incorporating bis(arene)chromium 4 or bis(arene)vanadium compounds chemically bonded into the macrochains.Novel bis(arene)chromium-containing polyacrylonitrile materials have been prepared by the reaction between acrylonitrile and the corresponding bis(arene)chromium complex (or mixture) in the absence of solvent under argon. 4 A cyanoethylation reaction mechanism (Scheme 1) was proposed by Domrachev and Razuvaev to account for APPLIED ORGANOMETALLIC CHEMISTRY

A polarising interferometer was used to investigate changes in the refractive index of an Nd : YAG laser crystal associated with changes in the populations of the electronic energy levels characterised by different polarisabilities. The study was carried out on diode-pumped crystals as well as on crystals which were flashlamp-pumped under conditions of saturation of the gain experienced by the optical beam. The changes in the refractive index depended nonlinearly on the pump power. The ratio of the real and imaginary parts of the nonlinear susceptibility of an Nd : YAG laser amplifier was determined: this ratio rose from 0.2 to 1.2 when the gain increased from 0.2 to 0.45 cm À1 .

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