Structure of the Elusive Hydrido(methylcyclopentadienyl)dicarbonylmanganate(I) Anion, [(η⁵-C₅H₄Me)Mn(CO)₂H]^-, as Determined by Single-Crystal X-ray Diffraction

The reactive [(η5-C5H4Me)Mn(CO)2H]- anion has been stabilized with the large counterion [K(18-crown-6)]+, and its structure has been determined by an X-ray diffraction study of a single crystal, which shows the unit cell to contain two inequivalent [K(18-crown-6)][(η5-C5H4Me))Mn(CO)2H] ion pairs. The anion adopts a three-legged piano-stool geometry in the crystal, with a C5Mn(CO)2 geometry very similar to that found in [(η5-C5H5)Mn(CO)3]. Salient bond distances (Å) and angles (deg) are as follows: Mn−H = 1.565(19)/1.54(2); Mn···K = 3.6186(11)/3.5874(11); K···H = 2.833(17)/2.771(19); (O)C−Mn−C(O) = 89.83(11)/90.87(10); and Mn···H···K = 107.2(6)/109.2(8). The structure of [(η5-C5H4Me)Mn(CO)2H]- is compared with those reported for bridging hydride and σ-bond complexes derived from the [(η5-C5H4R)Mn(CO)2] moiety.