Synthesis, Structure, and Spectroscopy of Pseudotetrahedral Co¹¹N₃(SR) Complexes. Active Site Approximations to the Cobalt(II)-Substituted Type 1 Copper Proteins

Complexes of the stoichiometry Co¹¹N₃(SR) were prepared by the reaction of CoCl(SR)(SR = O-ethylcysteinate) with potassium hydrotris(3,5-dimethyl-l-pyrazolyl)borate, K(HB(3,5-Me₂pz)₃). or by the reaction of CoBr(HB(3.5-Me₂pz)₃with NaSR (SR = p-nitrobenzenethiolate or pentafluorophenylthiolate). These complexes are synthetic approximations to a proposed active site in the cobalt(lI)-substituted blue copper proteins. The complexes were characterized by electronic spectral, NMR, and XPS techniques. The complex pentafluorophenylthiolato(hydrotris(3,5-dimethyl-l-pyrazolyl)borato)-cobalt(II) was also characterized by single-crystal X-ray diffraction methods. The complex crystallizes in the monoclinic space group C_2h⁵-P2/n with four molecules in a unit cell of dimensions a = 15.46 (1) Å, b = 7.841 (8) Å, c = 22.20 (2) Å, and β = 91.89 (2)° (-162°C). Least-squares refinement of the 106 variables has led to a value of the conventional R index (on F) of 0.106 for 827 independent reflections having F₀²>3σ(F₀²). The geometry about the cobalt(II) ion, which is coordinated to three nitrogen atoms and one sulfur atom, is distorted tetrahedral, with N-Co-N angles ranging from 89.3 (7) to 94.1 (7)° and with N-Co-S angles ranging from 107.7 (6) to 138.3 (6)°. The Co-N distances range from 1.97 (2) to 2.01 (2) Å, and the Co-S distance is 2.26 (1) Å.