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New tricks for an old dog: The solid-state structure of cis-[W(CO)4(piperidine)2] reveals an intermolecular, bifurcated H-bonding network involving the N-H protons and the two CO ligands trans to the piperidine ligands (see X-ray crystal structure; C gray, H green, N blue, O red, W magenta). Such an arrangement accounts for νCO absorptions as low as 1768 cm−1!
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Braunstein et al. (2004) studied this question.
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