COMPARATIVE STRUCTURAL STUDIES OF [(ETA(5)-ME5C5)IR(I)(2,2'-BIPYRIDINE-4,4'-COOH)] AND II)(2,2'-BIPYRIDINE-4,4'-COO(CH2)3-PYRROLE)CL]CLO4

(2,2'-Bipyridine-4,4'-dicarboxylic acid)(eta5-pentame-thylcyclopentadi enyl)iridium(I) (3), [Ir(C10H15)-(C12H8N2O4)], M(r) = 571.64, monoclin ic, C2/c (No. 15), a = 17.870 (5), b = 12.045 (4), c = 18.641 (3) angs trom, beta = 100.66 (3)-degrees, V = 3943.1 angstrom3, Z = 8, D(x) = 1 .926 g cm-3, lambda(Mo Kalpha) = 0.70926 angstrom, mu = 67.76 cm-1, F( 000) = 2224, room temperature, final R = 0.043 for 2733 observed refle ctions with I > 5sigma(I). {Bis[3-(1-pyrrolyl)propyl] oro(eta5-pentame thylcyclopentadi-enyl)iridium(III) perchlorate (4), [IrCl(C10H15)(C26- H26N4O4)]ClO4, M(r) = 920.86, monoclinic, P2(1)/c, a = 9.870 (3), b = 14.908 (8), c = 25.931 (5) angstrom, beta = 96.91 (2)-degrees, V = 378 8 (2) angstrom, Z = 4, D(x) = 1.615 g cm-3, lambda(Mo Kalpha) = 0.7092 6 angstrom, mu = 3 7.05 cm-1, F(000) = 1840, room temperature, final R = 0.069 for 3173 observed reflections with I > 3sigma(I). Complex (3) is the first structurally characterized Ir(I)Cp species. The Ir atom has a five-coordinate environment with Ir-N(1), Ir-N(2) and Ir-Cp(ce ntroid) distances of 2.064 (7), 2.068 (6), 1.835 angstrom, respectivel y. The bipyridine mean plane makes on angle of ca 75-degrees with the pentamethylcyclopentadienyl (Cp) mean plane; the deviation from ortho gonality may arise from the tendency of the Cp ring to behave as an e ta3-allyl ene ligand rather than an eta5-Me5C5 ligand, in accordance w ith the presence of two long Ir-C(Cp) distances [2.278 (8) and 2.273 (8) versus 2.149 (9)-2.172 (8) angstrom for the other Ir-C(Cp) bond l engths]. Complex (4) has a typical three-legged 'piano stool' structur e with Ir-N(1), Ir-N(2), Ir-Cl and Ir-Cp(centroid) bond distances of 2.12 (1), 2.12 (1), 2.399 (6), 1.801 angstrom, respectively. In comple xes (3) and (4) the Ir-Cp distances are unusually short due to the st rong pi-acceptor properties of the bipyridine ligands.