STRUCTURE OF BIS-KISPYRAZOLYLBORATE AND TRIS-KISPYRAZOLYBORATE AND TETRAKISPYRAZOLYLBORATE IN THE SOLID-STATE (SODIUM AND POTASSIUM-SALTS OF TETRAKISPYRAZOLYLBORATE BY X-RAY CRYSTALLOGRAPHY) AND IN SOLUTION (H-1, B-11, C-13 AND N-15 NMR)

The knowledge of the properties of pyrazolylborates has been considerably improved both in the solid state and in solution. The hydrates of the sodium and the potassium salts of tetrakis(1-pyrazolyl)borate crystallize in the space group C2/c, both salts being isomorphous. Regular pyrazole rings conform with a pseudosymmetry plane around a distorted tetrahedral boron atom. Chains along the b axis of two different octahedra of coordination, sharing water oxygens, are linked by H bonds. In solution, a careful H-1, C-13, B-11 and N-15 NMR study was carried out. The applicability of the rules used to assign H(3) versus H(5) and C(3) versus C(5) in the case of pyrazolylborates was reevaluated. Only for tetrakis(1-pyrazolyl)borate were couplings observed with B-11 in H-1, C-13 and N-15 resonances. The regularity of the properties of bis-, tris- and tetrakispyrazolylborates, allows the calculation of the spectral parameters of the still unknown tris-hydrido(1-pyrazolyl)borate, pzBH3-. Finally, the electronic properties, as measured by sigma-p, of the substituents BH3-, pzBH2-, pz2BH- and pz3B- were estimated.