The compound fac-Re(bpy)(CO) 3 (COCH 3 ) (1) (bpy=2,2'-bipyridine) with three different kinds of π-acceptor ligands coordinated to rhenium(I) has been investigated by infrared spectroelectrochemistry to reveal the occupation of the π*(bpy) MO on one-electron reduction to 1 - with negligible participation of the π-accepting acetyl group. The results are discussed in relation to the spectroscopy (NMR, IR) and the crystal structure analysis of the neutral complex 1, which reveals a short C O(acetyl) (1.157(12) A) and a long Re C(acetyl) bond (2.245(12) A) and an orientation of the Re C(O)CH 3 plane parallel to the C 2 axis of the coordinated bpy. The result is an orthogonal arrangement of d x z /π*(bpy) and d x y /π*(acetyl) orbitals. This situation stands in distinct contrast to the structure reported for the complex salt [Re(L)(CO) 3 (COCH 3 )](PPN) (PPN + =bis(triphenylphosphoranylidene)ammonium) with a cyclometallated 2-phenylpyridine ligand L. The crystal structures of the related complexes [M(bpy)(CO) 4 ](OTf), M=Re and Mn, were determined for comparison.