Title

Hydrotris[3-(2′-thienyl)pyrazol-1-yl]borate: A Ligand of Remarkably Low Steric Requirements

Abstract

The new ligand hydrotris[3-(2′-thienyl)pyrazol-1-yl)borate (=L*) was prepared and shown to have the second-lowest steric hindrance among the known poly(pyrazolyl)borates. It forms octahedral L*2M 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-Pri-4-Br-pz)3CoCl to form octahedral HB(3-Pri-4-Br-pz)3CoL*, having C3v symmetry. The structure of L*2Co 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 Å3, Z = 4. The structure was refined to R, Rw = 0.062, 0.065 by using 3670 diffractometer-collected data. Form B: triclinic, P1 (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 Å3, Z = 1. The structure was refined to R, Rw = 0.044, 0.043 by using 4380 diffractometer-collected data. The Mössbauer effect hyperfine parameters for L*2Fe, 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.

Department(s)

Chemistry

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 1991 American Chemical Society (ACS), All rights reserved.


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