Hydrotris[3,(2'-thienyl)pyrazol-1-yl]borate: a ligand of remarkably low steric requirements
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Inorganic Chemistry, ISSN: 0020-1669, Vol: 30, Issue: 13, Page: 2795-2801
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The new ligand hydrotris[3-(2′-thienyl)pyrazol-l-yl)borate (=L*) was prepared and shown to have the second-lowest steric hindrance among the known poly(pyrazolyl)borates. It forms octahedral L*M complexes with first-row transition-metal ions but fails to yield stable L*MX species, except with Zn(II). It also reacts with HB(3-Pr-4-Br-pz)CoCl to form octahedral HB(3-Pr-4-Br-pz)CoL*, having Csymmetry. The structure of L*Co was determined by X-ray crystallography. Two different crystal forms of the molecule in different conformations are reported. Form A: monoclinic, C2/c (No. 15), a = 21.577 (2) Å, b = 12.464 (1) Å, c = 18.298 (2) Å, β = 113.21 (1)°, T = -70 °C, V= 4522.6 Å, Z = 4. The structure was refined to R, R= 0.062, 0.065 by using 3670 diffractometer-collected data. Form B: triclinic. [formula omitted] (No. 2), a = 10.148 (2) Å, b = 11.768 (2) Å, c = 12.241 (3) Å, α = 61.54 (1)°, β = 69.06 (1)°, γ = 67.19 (1)°, T=-70°C, V= 1157.5 Å, Z= 1. The structure was refined to R, R= 0.044, 0.043 by using 4380 diffractometer-collected data. The Mössbauer effect hyperfine parameters for L*Fe, obtained at 78 and 295 K, are typical of distorted high-spin octahedral iron(II) complexes, but the asymmetric line widths found in the quadrupole doublet indicate the presence of a reduced relaxation rate for the effective paramagnetic hyperfine field. © 1991, American Chemical Society. All rights reserved.