[en] The title compound has been prepared by the reaction of tricyclopentadienyluranium chloride (UCp₃Cl) and sodium pyrazolate (NaC₃H₃N₂) in tetrahydrofuran (THF). The compound has been characterized by its infrared, visible-near-IR, ¹H NMR, and mass spectra and by single-crystal x-ray diffraction. The molecular structure consists of discrete UCp₃(C₃H₃N₂) molecules in which the uranium(IV) ion is coordinated by three eta⁵-Cp rings in a nearly trigonal array similar to that of other lanthanide and actinide MCp₃X structures. However, unlike these other structures, an 11-coordinate geometry is achieved by having both the adjacent nitrogen atoms of the pyrazolate ring coordinate to the metal ion such that the local twofold axis of the pyrazolate ring and the local threefold axis of the UCp₃ fragment coincide. This is the first example of this type of endo-bidentate eta² coordination for the pyrazolate anion. Red-brown crystals from toluene conform to space group P2₁/a (an alternate setting of P2₁/c) with a = 14.295 (1) A, b= 8.383 (1) A, c = 14.282 (1) A, β = 112.80 (1)⁰, and four molecules per unit cell. For the 3631 independent reflections collected by counter methods with F² > 3sigma(F²), the final weighted and unweighted R factors are both 3.14%. The U-N distances are 2.40 (1) and 2.36 (1) A. The average U-C distance of 2.76 A is consistent with that predicted for an 11-coordinate uranium (IV) cyclopentadienyl complex. The 90-MHz proton resonances of the Cp rings occur at -9.51 (35⁰C), -11.59 (-10⁰C), -14.22 (-50⁰C), and -15.84 (-75⁰C) ppM. Susceptibility studies from 5 to 80 K show a temperature-independent paramagnetism from 7.5 to 37.1 K; above this temperature μ/sub eff/ = 2.67 μ/sub B/