The (nitrido)chromium(V) derivative [PW 11 O 39 {CrN}] 5-(1a) was synthesized by the reaction of the monolacunary [H 3 PW 11 O 39 ] 4-polyanion with a {CrN} 2+ function generated in situ. The EPR spectrum of the formed polyoxometalate confirmed the presence of a paramagnetic Cr V complex, and the presence of the nitrido bond was inferred by IR spec-

Chromium I 5500 A (Nitrido)chromium(V) Function Incorporated in a Keggin-Type Polyoxometalate: [PW 11 O 39 CrN] 5--Synthesis, Characterization and Elements of Reactivity.-Title compound (III) contains an in situ formed N≡Cr 2+ unit within the monolacunary PW11 anion. The EPR spectrum of (III) confirms the presence of a paramagnetic Cr V complex, and the presence of the nitrido bond is inferred by IR spectroscopy. (III) shows nucleophilic behavior towards TFAA as demonstrated by the formation of (IV). -(LAHOOTUN, V.; KARCHER, J.; COURILLON, C.; LAUNAY, F.; MIJARES, K.; MAATTA*, E.; POUST, A.; Eur.