Structure determination of bromotricarbonyl([eta]-cyclopentadienyl)molybdenum(II)

This is the published version. Copyright 1990 by International Union of Crystallography.[(77-C5Hs)Mo(CO)3Br], Mr = 324-97, monoclinic, P2x/n, a = 8-186(3), b= 10-536(3), c =11-391 (3) A, p = 99-58 (2)°, V= 968-7 (6) A3, Z = 4, Dx = 2-228 g cm- 3 , A(Mo Ka) = 0-71069 A, fi =56-68 cm"1, F(000) = 616, r = 1 1 3 ( l ) K , final R =0-0261 for all 1271 independent reflections. The molecule adopts a distorted square pyramidal coordination environment about the Mo atom. The shorter Mo—C bond of the carbonyl ligand trans to the bromide apparently arises from the lack of competition for d7r bonding electrons. The longer Mo—C bonds for the mutually trans carbonyl ligands, and the squashed trans C—Mo—C angle (approximately 28° smaller than the Br—Mo—Ctrans angle) result from sharing one pair of dir bonding electrons. Selected bond distances and angles: Mo—Br =2-651(1), av. Mo—Ccis = 2-020 (6), Mo—Ctrans =1-978 (7), Mo—CPcent = 1-993 (1), av. (C—0)cis =1-132(5), (C 0)trans =1-154 (9), B r - M o - C , r _ =136-7 (2), Br—Mo—Ccis = 77-0 (3), Br—Mo-CP^= 112-04(3), av. Ctrans—Mo—C^=78-l(2), av. Cc£s—Mo—CPeent = 125-8 (2), Ctrans— Mo—CPeent *111-3 (2)