Specific solvatochromism of the prototypical olefin complexes (h2-TCNE)M(CO)5 (M = chromium, tungsten) resulting from n and p donation of aprotic solvents toward the p-acceptor ligand. Organometallics, (10)2:410--415, 1991. [PUMA: carbonyl chromium solvatochromism tetracyanoethylene tungsten]